Earth-Pages Archive News, Anthropology

March and April 2010 were indeed exciting times for palaeoanthropology, with publication of evidence for two new species of hominin. Cave systems in the Archaean limestones of north-eastern South Africa have yielded so many fossil remains related to human evolution that the area liberally dotted with them has UN World Heritage status. The caves formed beneath a now-eroded plateau, and are so rich because creatures fell into surface sink holes, died and remained little disturbed by scavengers. The latest find has an unusual story behind it (Balter, M. 2010. Candidate human ancestor from South Africa sparks praise and debate. Science. v. 328, p. 154-155). The cave system was first explored by lime-kiln workers around the early 1900s, who brought out blocks which litter the ground around cave mouths. It was in one of these chunks that the 9-year old son of a South African palaeoanthropologist found bone that turned out to be a hominin lower jaw. Sadly, young Matthew Berger had to be excluded from the list of authors of the two important papers that ensued from his find, because of Science magazine's rules for authorship (Berger, L.R. et al. 2010. Australopithecus sediba: a new species of Homo-like australopith from South Africa. Science, v. 328, p.195-204. Dirks, P.H.G.M. and 11 others 2010. Geological setting and age of Australopithecus sediba from southern Africa. Science, v. 328, p.205-208). Nevertheless, he can be well satisfied as the full set of bones points to a new species, one that may arguably share more features with Homo species of about the same antiquity than any other australopithecine. Being coeval with H habilis, A. sediba cannot be ancestral but may have shared a common ancestor with the earliest known human species. Fitting the new find into the long and variously disputed cladistics of hominins will run and run, but at least it should re-emphasise one thing: there were several cohabiting hominin species in Africa around 2 Ma ago.

Such a multiplicity of co-existing hominins seemingly continued until quite recent times, as a remarkable piece of evidence from a Siberian cave has confirmed. Between about 30 to 48 ka, the cave was a popular venue for Neanderthal hunters who left tools and bones of their prey. Russian archaeologists combed the cave deposits for human remains but came up with only fragmentary finds of bone. One of these was the tip of someone's little finger. The possibility of obtaining genetic material from relatively young finds in caves that have remained cold and untouched encouraged the excavators to handle their finds carefully. It's just as well they did for the results from the Max Planck Institute for Evolutionary Anthropology in Leipzig Germany, famous for its work on Neanderthal DNA, held a surprise. The finger's owner was neither a Neanderthal nor a fully modern human (Krause, J. et al. 2010. The complete mitochondrial DNA genome of an unknown hominin from Southern Siberia. Nature, v. 464, p. 894-897). The evidence for this is overwhelming. Fully modern human mtDNA ranges from 0 to about 100 differences in nucleotide positions, the difference between human and Nenaderthal mtDNA is just over 200, but the pinky bone revealed almost 400 differences from ourselves and almost as many from Neanderthals. Such differences suggest that ancestors of the unknown Siberian separated from the line of descent to Neanderthals and modern humans about a million years ago. Yet all three were in Asia a mere 40 ka ago. Add to that the diminutive H. floresiensis who survived to cohabit Flores with modern humans until about 9ka, and some evidence that H. erectus was also around in Java up to 25 ka, gives possibly 5 species of human in Asia who may have met and goodness knows what else.

See also: Dalton, R. 2010. Fossil finger points to new human species. Nature, v. 464, p. 472-473.

Yes, it seems thay they did...

Perhaps now the myth of brutish Neanderthals will finally be laid to rest. Thanks to the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, we have a nuclear genome of H. neanderthalensis; in fact a composite based on bones of three individuals from a Croatian cave. Carbon-14 dating shows that the bones are between 44 to 38 ka old: about the time of the first arrival of fully modern humans in Europe. Only ten years on from the publication of the first human genome, the team inspired by Svante Paabo (actually the last of 56 authors, but the founder of the lab and its peerless facilities) has engineered a scientific triumph that matches the achievement in 2000 led by James D. Watson at the U.S. National Institutes of Health and Craig Ventner of Celera Corporation (Green, R.E. and 55 others 2010. A draft sequence of the Neandertal genome. Science, v. 328, p. 710-722). Let's be frank, to get to know another member of our genus nearly as well as ourselves, albeit in terms of A, C, T and G the nucleotide bases of DNA adenine, cytosine, thymine and guanine, puts the rest of science in somewhat distant perspective. It forms the basis for learning what, if anything, sets us apart from earlier humans, what we share with them and potentially how we came to be what we are.

Apart from a geologically brief period since 80 ka when fully modern humans and Neanderthals occupied the Mediterranean fringe of the Middle East, both had probably developed separately since forebears of the Neanderthals left Africa to arrive in Europe about 400 ka ago while ours seem to have stayed in Africa. Earlier genetic results show that both species shared a common ancestor, perhaps H. heidelburgensis. From the time when the main wave of African people ventured into Arabia, Asia and Europe, perhaps around 60 to 75 ka, chances are that encounters were inevitable, until the last Neanderthals met a lonely end on the Rock of Gibraltar around 25 ka. Variations in mtDNA data seem to show that the two species have little genetic overlap, but mitochondria hold only a small part of DNA. The 4 billion base pairs of nuclear DNA occur in thousands of segments that have evolved independently, and in us continue to do so: a source for very detailed comparisons indeed. The issue centres on how alike and how different such segments are, when compared with DNA from different modern human genomes. If similarities and contrasts are more or less the same in comparison with all modern human groups, then it is most likely that although Neanderthals and modern humans did meet they did not exchange genetic materials; i.e. they did not mate successfully. The new data show beyond much doubt that Neanderthals were more similar genetically to modern Europeans and Asians than they were to modern Africans. There was successful mating and the progeny entered the fully modern human population of Asia and Europe, to the extent that Asians and Europeans host 1 to 4% of Neanderthal ancestry.

The most famous human in genetics, simply because he arranged sequencing of his own DNA, which is the comparator used by the team, Craig Ventner can be highly confident that he contains segments of Neanderthal DNA. We must await his reaction in a mood of solemn gaiety, and react he most probably will: I did and I feel quite cheerfully proud. Interestingly, Neanderthals are as closely related to individuals from New Guinea and China as they are to a French person. Such uniformity among non-Africans suggests that the gene exchange (viz. sexual intercourse) took place shortly after fully modern humans migrated out of Africa. But who did what to whom under which circumstances will remain a mystery, although it appears that the gene flow was from Neanderthal to human and not vice versa. With a small colonising group of Africans, there need not have been a great deal of 'sharing' of bodily fluids for introduced genes to 'surf' throughout succeeding generations to reach us. So what is it that we lucky ones share with Neanderthals? This is a topic fraught with possible overtones, though they probably will not suit the outlook of those with a prejudiced racist tendency. The results suggest 15 genomic regions that include those involved in energy metabolism, possibly associated with type 2 diabetes; cranial shape and cognitive abilities, perhaps linked to Down's syndrome, autism and schizophrenia; wound healing; skin, sweat glands, hair follicles and skin pigmentation; and barrel chests. Some may have been beneficial others not, but they have been retained through thousands of fully modern human generations.

Analyses of the genome are at a very early stage, but the sequencing technique and associated checks for contamination with modern DNA are sufficiently advanced that other Neanderthal remains and bones of ancient Europeans and Asians will surely add to the excitement. Just how far back analyses can be pushed remains to be seen, but it is now quite clear that human evolution was a great deal more complicated than the simple Out-of-Africa model that is currently almost universally accepted.

See also: Gibbons, A. 2010. Close encounters of the prehistoric kind. Science, p. 680-684.

Neanderthal �bling�

Led by Jo�o Zilh�o of the University of Bristol, UK, a team of British, French, Italian and Spanish archaeologists and anthropologists have at a stroke rid our former companions in Europe, the Neanderthals, of the popular and academic stigma of being uncultured (Zilhao, J. and 16 others 2010. Symbolic use of marine shells and mineral pigments by Iberian Neandertals. Proceedings of the National Academy of Sciences, v. 107 p. 1023-1028). They wore jewellery in the form of necklaces and pendants of bivalve shells, remains of which have turned up in large numbers in caves and rock shelters in the interior of southeast Spain. Some of the perforated shells show clear signs of having been painted, and a few show grooves worn by string. They found even a paint container and painting tools made of small bones from a horse�s foot. The container and tools retain distinct traces of pigment made from the common iron colorants goethite, jarosite and hematite. One large, perforated scallop shell shows that its white interior was painted to match its reddish exterior.

It has often been commented that Neanderthal adornments ( a few possible finds precede this work) and intricate tools were simply copied from those of fully modern humans. The deposits containing this ornamentation are around 50 thousand years old: preceding modern human occupation of the Iberian Peninsula by at least 10 ka. Evidence for artistic work by early H. sapiens comes from South Africa as far back as 165 ka (see Technology, culture and migration in the Middle Palaeolithic of southern Africa in January 2009 EPN, and When and where �culture� began in EPN of November 2007). Iron-based pigments are still widely used for body painting in many societies, but obviously that use will not feature directly in archaeological finds. Association of lumps of potential pigments with hominin tools go back even further in Africa, beyond the presence of fully modern humans, but to ascribe pieces of say hematite to cultural practice needs evidence for scraping or grinding. There seems no reason why Neanderthals and modern humans maintained an ancient cultural tradition.

Evidence for early journeys from Africa to Asia

A fragile consensus has developed concerning the date when fully modern humans left Africa then migrated to all habitable continents. It is based on genetic comparisons among living people, very sparse occurrences of H. sapiens remains that have been dated and on the environmental pressures in Africa to migrate during the highly erratic deterioration of climate since the last interglacial. The last included a series of abrupt cooling and drying episodes around 118, 110, 86, 75, 71 and 67 ka. That fully modern humans entered the Middle East from time to time between 130 and 75 ka is backed up by actual fossils, but most palaeoanthropologists believe that they moved no further, because of the growth of surrounding deserts, and probably did not return until around 45 ka. The consensus for the decisive move out of Africa to Eurasia is that it was via the Straits of Bab el Mandab at the entrance to the Red Sea, when sea level fell to a level that would have allowed a crossing by rafting over narrow seaways. The most likely was during the brief 67 ka cool/dry episode that coincided with an 80 m fall in global sea level: the largest since the previous glacial maximum. This would fit the earliest dates of fully modern human remains in Asia and Australasia. There had been falls of more than 50 m around 110, 86 and 75 ka, each followed by rising sea level. Each of them accompanied by cooling and drying in Africa conceivably could have allowed earlier migrations from Africa to southern Arabia. Emerging data seems set to complicate matters.

At a conference in Gibraltar during September 2009 (Balter, M. 2009. New work may complicate history of Neandertals and H. sapiens. Science, v. 326, p. 224-225) there were further reports of stone tools, which apparently resemble those of a similar age from Africa, beneath the 74 ka Toba ash in South India, and dated between 70 to 80 ka old in the Yemen and United Arab Emirates. Even more challenging are reports of archaic H. sapiens teeth and a jawbone with a chin � a sure sign of a fully modern human � from cave sediments in southern China that yield a date of about 110 ka (Stone, R. 2009. Signs of early Homo sapiens in China. Science, v. 326, p. 655). Given an opportunity and a need humans do tend to move in order to survive, a proclivity that would undoubtedly be boosted by our insatiable curiosity: after all H. erectus, antecessor and neanderthalensis all made tremendous migrations starting more than 1.6 Ma ago.

Fungal clue to fate of North American megafauna

More than 30 large mammal species, including elephants and giant sloths, that had roamed North America during the Pleistocene met their end between 13 and 11.5 ka. Whether or not predation by newly arrived humans caused these extinctions remains unresolved, as do the triggers for coinciding changes in plant communities and evidence for increased burning of biomass. While the ages of fossil bones are direct evidence for species being present, they are not found everywhere that a megafauna likely lived and occurrences are patchy in time. There is however a proxy for the presence or absence of large herbivores: spores of fungus that thrived on their dung (Gill, J.L. et al. 2009. Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America. Science, v. 326, p. 1100-1103). Sporormiella can only complete its life cycle after herbivores have digested plant matter. So its spores in sediment cores form an impressive link to the local presence of herds. In a lake core from New York State such fungal spores, having been much more abundant beforehand, fell to less than 2% of all spores and pollen about 13.7 thousand years ago. This suggests that large herbivores vanished from this area at that time.

Interestingly, the timing is during a warm period (the B�lling-Aller�d) rather than the stress of the Younger Dryas glacial re-advance. Moreover, the local disappearance predates the first signs of Clovis people, although there is evidence for earlier human colonisers back to 15 ka. It is possible that it was the disappearance of large herbivores that allowed the development of extensive mixed coniferous-deciduous woodland, broad-leaved trees having perhaps been browsed severely by earlier herbivores.

Early hominin takes over Science magazine

I first mentioned Ardipithecus ramidus in EPN for February 2002 (Taking stock of hominid evolution), and the remarkable first finds by Tim White and his team were in 1994. Fifteen years on, and having amassed fragments of at least 36 individuals (and thousands of vertebrate, invertebrate and plant fossils) - Owen Lovejoy of Kent State University remarked, 'This team seems to suck fossils out of the ground' - it's pay day! A total of 54 pages of the 2 October 2009 issue of Science (v. 326, Issue 5949) are devoted to this diminutive and very old (4.4 Ma) hominin. Such mounds of data wrested from the cauldron of the Afar Depression needed a long incubation period, and what is presented in Science is a summary rather than being comprehensive: much more is available online, and yet to come. The now hugely experienced, 47-strong academic team built up by Tim White and his original colleagues deserve massive congratulations. But they depended on the eagle-eyed, mainly Ethiopian fossil finders, many of whom are Afar pastoralists who took to field palaeontology as ducks to water. Science in general owes a massive debt to all those who have wrested such a wealth of anatomical information from every aspect of the fossils and their environmental context. What they have achieved is more worthy of Nobel-status than the fumbling of gaggles of annual economist-laureates who still cannot grasp why the world economy continually does grave disservice to humanity. The Ar. ramidus team also have a lot more worth saying to us than those physicists who seek the grail of a theory of everything - racked by such hubris that they are both unintelligible and unrealistic in the most literal way.

I cannot do adequate justice to the work in that historic issue of Science, but there are some general points that will leave any interested person breathless. As regards previous assumptions about the environment under which hominins emerged, it was woodland not open savannah. Though upright and capable of walking, as revealed by pelvis remains, Ardipithecus had feet with opposable big toes: sort of foot-thumbs. So they would have been as comfortable on trees as on the ground. Yet, their foot-architecture shows signs of having evolved from monkey-like feet rather than any lin=ke those of modern gorillas and chimps. A degree of certainty accompanies anatomical discussions, for one individual female Ar. ramidus is represented by a large proportion of a full skeleton, rivalling the later remains of 'Lucy', an Australopithecus afarensis. Her skull, reconstructed from a badly crushed state using co0mputed tomography and digital piecing-together, gives a brain size around the same as bonobo chimpanzees, and less than that of australopithecines. The feet clearly show a walker able to clamber, rather than swing and knuckle walk. Hands, though primitive, are more human-like than those of living apes are. From that can be concluded that a common ancestor a million of so years earlier was not ape-like in manual terms: chimps have evolved in this respect perhaps a lot more than those on the human line. Teeth shape, wear and isotopic signatures suggest a broad diet, rather than specialisation, from which grasses and grass-eating prey seem absent. Moreover, there is no sign of large canines, that could indicate minimal social aggression. Males and females were of similar size, as are we, rather than showing the sexual dimorphism that characterised later australopithecines and both chimps and gorillas. This also seems to point backwards in time to the last common ancestor of ourselves and chimps being very different from both living genera. Yet in many respects chimps seem to have evolved more than hominins. Because of the work on Ar. Ramidus, a chimpanzee-centric view of our shared forebears and therefore of hominin evolution can now be rejected. Perhaps thankfully, speculation about aspects of our behaviour stemming from those of chimpanzees is probably worthless.

The mass of data concerning this small, Pliocene hominin holds out a promise of yet more to come, both further back in time, and to populate the gaps in time and morphology that currently plague palaeoanthropology. The terrestrial sediments in which White et al. found Ar. Ramidus are 300 m thick, cover 5.5 to 3.8 Ma and are exposed over a large area. The stratum from which most data were recovered represents at most about 10 thousand years. Elsewhere in the Afar-Danakil Depression are other sediments laid down in river and lake systems that go back as far the Miocene (the estimated time of the last common ancestor of other primates and humans), and are still being deposited today. If anything characterised this triumph of the human intellect, it combined patience, determination and an attention to detail that was shared by every participant.

Fire and tool making

Native people in Australia have been spoiled for choice of materials from which to make superb stone tools, all kinds of silica rock being available in the bedrock and the widespread tropical soils, including multicoloured chalcedony and even opal. Their master craftsmen developed a form of heat treatment that subtly modifies silica�s internal structure so that gentle application of pressure to the edges of lumps removes small flakes to give intricate sharp edges, including barbs for fishing spears. This pyrotechnology leaves easily recognised signs in stone tools: colour changes and a pearly lustre.

A large team of archaeologists and geoscientists from South Africa, Australia, the UK and France have sifted through tools collected from the 35 to 280 ka African Middle Stone Age (defined differently from the European Mesolithic) in search of evidence for fire treatment (Brown, K.S. and 8 others 2009. Fire as an engineering tool of early modern humans. Science, v. 325, p. 859-862). Like signs of symbolic behaviour (see Technology, culture and migration in the Middle Palaeolithic of southern Africa and Deeper roots of culture in January and March 2009 issues of EPN) fire-worked silica tools appear as early as 164 ka ago. However, this is the first paper that reports a search for such technology, and since fire was definitely used by even earlier humans, such as Homo antecessor around 790 ka (see Early, microscopic evidence for human control of fire in November 2008 issue of EPN) expect earlier finds to be announced.

See also: Webb, J. and Domansski, M. 2009. Fire and stone. Science, v. 325,p. 820-821

Neanderthals few on the ground

Analysis of DNA from Neanderthal bones is gathering pace as cheaper and more reliable methods for sequencing emerge. The latest breakthrough is by a team working in Svante P��bo�s lab at the Max-Planck Instuitute for Evolutionary Anthropology in Leipzig, Germany, which has defined full mitochondrial DNA sequences for five individuals (Briggs, A.W. and 17 others 2009. Targeted retrieval and analysis of five Neandertal mtDN genomes. Science, v. 325, p. 318-321). The samples are from almost the full geographic range known for Neanderthals, from Spain in the west to the eastern shore of the Black Sea in Russia, and are from 38 to 70 ka old; i.e. probably pre-dating the main influx of fully modern humans into Europe. The results show that the range of genetic diversity in the female line was only one third that found in humans today. That suggests that, compared with the modern human diaspora from Africa, total numbers of Neanderthals was low over the period analysed, and perhaps since their first colonisation of Europe and the Eurasian steppes around 400 ka.

See also: Wong, K. 2009. Twilight of the Neandertals. Scientific American, v. 301 (August 2009), p34-39.

Klondike gold rush pays dividends for Pleistocene

The 1896 discovery of gold in the Yukon Territory, Canada triggered the Klondike gold rush, which led to environmental wreckage that continues to this day. The placer deposits are in permanently frozen, but fragile alluvial sediments dating back as far as 700 ka. But as well as gold washed in by the Yukon�s rivers, the permafrost contains exceptionally well preserved records of the area�s late Pleistocene flora and fauna. The reason why that was possible at such high latitude (65°N) through 6 or 7 glacial interglacial cycles is that it remained free of ice sheets for most of the Pleistocene. Fossils finds in the placer deposits therefore document the conditions on the western edge of the Bering Straits land bridge, or Beringia, which emerged each time that sea level fell during glacial maxima (Froese, D.G. et al. 2009. The Klondike goldfields and Pleistocene environments of Beringia. GSA Today, v. 19 (August 2009), p. 4-10). Beringia was the route presented to the earliest Asian human migrants into the Americas, possibly even before the Last Glacial Maximum 22 ka ago. Much of the evidence comes from wind-blown loess deposits that are prone to permafrost development. Also, being close to a number of active volcanoes the area was sporadically blanketed by ash deposits that are dateable by radiometric means, so a stratigraphy is possible even in the irregular and ice-disturbed sediments. During glacial episodes the area was steppe dominated by herds of bison, mammoths and horses; clearly a hunters paradise, despite the harsh conditions.

African genes

Much of the interpretation of the growing database of human genetic variability has so far focused on migration out of Africa and across the habitable continents. To some extent the largest variability, of Africans themselves, has been undersampled, but a multinational team of Africans and non-Africans has now begun to redress the balance (Tishkoff and 24 others 2009. The genetic structure and history of Africans and African Americans. Science, v. 324, p. 1025-1043) partly to study genetically-linked epidemiology and partly anthropology. The study centres on African�s own ideas about their identity/ethnicity as well as documented cultural and linguistic division, and covers 3194 individuals from 121 populations in the continent, African-American populations in 4 US cities and 60 other populations from outside Africa. The team expands knowledge tremendously, as expressed by the many intricate diagrams. They use the statistical method of Bayesian clustering to tease out the ancestral bases for the genetic patterns preserved by Africans, which appear to be based on 14 major ancestral groups that mostly tally with cultural and linguistic divisions. Overall, the picture is one of repeated mixing of populations through migrations within the continent, many within historic times such as the shift of West Africans south-eastwards, but also much earlier movements such as the ancestors of the San people of southern Africa. These remaining gatherer-hunter people together with central African pygmies and the Hadza and Sandawe of Tanzania share ancestry and also, except for pygmies, language that involves click-sounds � the pygmies abandoned their original language in favour of that of the groups that now surround them in the Equatorial rain forests. Of the three groups, the Hadza most maintain the genetic structure of the earliest ancestors on the continent, but all three shared a common ancestor about 35 Ka ago. Interestingly, comparison with people outside Africa confirms earlier studies that indicated a source population for the out-of-Africa migration in East Africa close to the Red Sea. The paper is necessarily condensed and so difficult to follow, but clearly opens up great vistas in understanding intricacies at which anthropologists have previously only guessed. Like the physical landscape of Africa, that of its population reflects the range of factors that have shaped human evolution and hence a great deal of its destiny.

See also: Gibbons, A. 2009. African�s deep genetic roots reveal their evolutionary story. Science, v. 324, p. 575.

Very old human footprints in Mexico?

In 2006 palaeoanthropologists in the Americas, already at loggerheads about evidence for pre-Clovis (pre 13 ka) colonisation, were rocked to their boots. A team from Liverpool John Moores University, Bournemouth University and the Mexican Geophysics Institute claimed to have found human footprints more than 40 ka old in a volcanic ash deposit (Gonzalez, S. et al. 2006. Human footprints in Central Mexico older than 40,000 years. Quaternary Science Reviews, v. 25, p. 201-222). The extensive site exposed by quarrying carries many apparent footprints, both human and non-human. Moreover, some of the prints are in convincing-looking trackways. The very old date was obtained by optically stimulated luminescence dating of quartz-grains that measures the time since the grains were last exposed to sunlight or thermal baking. Were it not for that result probably little fuss would have been made. Now this remarkable find is under serious challenge (Feinberg, J.M. et al. 2009. Age constrains on alleged �footprints� in the Xa;nene Tuff near Puebla, Mexico. Geology, v. 37, p. 267-270). This US-Mexican team applied Ar-Ar dating to the ash and found an age of about 1.3 Ma, confirmed by its association with reversed magnetic polarity in the deposit � at 40 ka the geomagnetic field was as it is today. On that basis, Feinberg and colleagues claim to have refuted the identification of human footprints, and claim that they are merely quarrying marks degraded by later weathering. The Xalnene Tuff in which the footprints were found was deposited in a lake that has been periodically filled and dried out. If the disputed features can be shown irrefutably to be footprints, then there are only two possibilities: either they date from a 40 ka lowstand when the tuff was rewetted and soft, or they are of Homo erectus who somehow found their way to the Americas after leaving Africa around 1.7 Ma ago and crossed the drying lake bed shortly after the tuff was ejected from a nearby volcano.

�Hobbit� news

Bones of at least 6 or 7 small people have turned up in the now famous Liang Bua cave on the island of Flores, Indonesia. Their stratigraphic positions span the period from 95 to 17 ka. There have been numerous claims that they do not represent a dwarfed human species � i.e. Homo floresiensis � but individuals who suffered from some form of pathological condition. The strongest evidence supporting that sceptical view is that the one near-complete skull does not fall on the well-established brain �body-size distribution that covers many species: it seems too small for either a normal pigmy modern human or a similarly diminutive H. erectus. Now crucial new anatomical evidence seems set to swing the balance. (Jungers, W.L. et al. 2009. The foot of Homo floresiensis. Nature, v. 459, p. 81-84; Weston, E.N. & Lister A.M. 2009. Insular dwarfism in hippos and a model for brain size reduction in Homo floresiensis. Nature, v. 459, p. 85-88). The foot bones of the most recent and most complete specimen are not like those of humans but more ape-like, although they show clear evidence of bipedalism. Interestingly, they seem to be more primitive than those of H. erectus, raising the possibility of an undocumented dispersal of perhaps from Africa into Eurasia as an ultimate ancestor. Curiously, the foot is disproportionately long compared with the rest of the skeleton; another bonus for �hobbit� fans. Not having a snout, H. floresiensis certainly was no ape, indeed the skull is best expressed as a scaled-down version of either H. erectus or H. habilis. As to extremely small brain size in relation to the body size of H. floresiensis, insular dwarfism of fossil hippos in Madagascar provides a useful analogue, as Weston and Lister suggest. In adulthood they also have disproportionately small brains. As with many puzzles in human evolution, the stir caused by these new discoveries maintains H. floresiensis as a �hot topic� and further excavations are inevitable � Flores has plenty of caves, as do many islands in the Indonesian chain.

See also: Lieberman, D.E. 2009. H. floresiensis from head to toe. Nature, v. 459, p. 41-42.

Flirting with hand axes

A biface, Acheulean hand axe is more than object of beauty produced by exquisite skill, this industrial genre was invented by African Homo ergaster around 1.6 Ma ago, became a central feature of Palaeolithic archaeology, and lasted until the last few hundred thousand years. Nobody doubts that production of these objects implies a brain that fashioned able to visualise a complex shape within a shapeless lump of rock and to devise a way of achieving it. Moreover, its longevity spanning several species of Homo to our own shows that skills were efficiently passed down through hundreds of thousand generations: possible evidence for linguistic skills in the makers and teachers. But what was it for? Experts have been at a loss to agree on a function: too heavy for hafting to a spear; more awkward for cutting than earlier Oldowan pebble fragments; produced with careful three-dimensional symmetry when a hand tool needs none; time consuming to make yet often found in great abundance and apparently hardly used. One idea is that they were in fact for throwing, in the manner of a discus, yet broken biface axes are rare. A more appealing hypothesis is that they were made for �show� as an element in human sexual selection (Kohn, M. & Mithen, S. 1999. Hand axes: products of sexual selection? Antiquity, v. 73, p. 518-526). Kohn and Mithen argued that the primary function of hand axes was to advertise a maker�s "good genes": an indicator of the knap�per�s geographic knowledge of suitable resources; his ability to execute a plan; his dexterity and patience; and his so�cial awareness. Those are all attractive qualities in a potential mate. They also suggested that the axes� often near-pristine quality and occurrence in great numbers at some sites indicate that once their purpose was served, they were thrown away: �That man is so cool, he must be good at surviving�. Ten years after Kohn and Mithen first mooted the hypothesis it has come under criticism by April Nowell and Melanie Lee Chang, of the universities of Victoria, Canada and Oregon USA, respectively (Nowell, A. & Chang M.L. 2009.The case against sexual selection as an explanation of handaxe morphology. Paleoanthropology, v. 2009, p. 77-88).

The critique begins by examining Kohn and Mithen�s interest in symmetry as an element in attractiveness, that Nowell and Chang concede, but consider to have arisen not in a sexual context but in development of vision, despite vision being an evolutionary �given� vastly older than hominins. After a discussion of how fully modern human females base their sexual choices on non-physical attributes of potential mates, such as "niceness," intelligence, sense of humour, compatibility, willingness to work hard and evidence that the partner in question is attracted to them, Nowell and Chang examine available archaeological evidence. Much of this concerns the �absence of evidence�. For instance, there is no evidence to suggest that females did not make hand axes and living females in gatherer-hunter societies do make tools. Other criticisms include: the absence of hand axes from Asia until migration there by H. sapiens [but the biface axe had not been invented when H. ergaster migrated there from Africa around 1.8 Ma]; not all biface axes are symmetrical [but they are nonetheless impressive]; and axes in large numbers generally occur where prey has been butchered, as at Boxgrove, and may have accumulated by hundreds of years of use and loss at such sites by seasonal hunting. The most serious criticism is that some hand axes do show minute patterns that indicate that they were used; although most axes have never been examined for wear patterns. My own conclusion is that the critique is based on absence of evidence for biface axes as ritual objects in sexual selection, but that is not evidence of absence, and I wonder if the 10 years taken to bring together contrary evidence has a bit to do with casting doubt on a not quite �PC� idea. There are many intriguing facets of the fossil and archaeological records of hominins, none more so than those which may have a cultural connotation, like ochre caches (see Deeper roots of culture in EPN of March 2009) and the tear-shaped Acheulean axe. For most we may never know their true context, but can be sure that any curiosity and imagination we apply are reflections of imaginative and curious forebears.

Homo erectus in a cold climate

The famous Zhoukoudian Cave where Peking Man, now known to have been Homo erectus, was first found in 1929 is a lugubrious place. It seems the hominin fossil remains of at least 40 individuals were dragged there and eaten, hopefully by predators. They are by no means the oldest Asian hominins at less than 1 Ma, and their ancestors, probably African H. ergaster, migrated that far around 1.6 to 1.8 Ma ago. Until this year, decent ages from Zhoukoudian were a problem: the errors on estimates of around 500 ka were too large (the likely time lies in a �datability gap� between the capabilities of Ar-Ar and ¹⁴C dating methods) to see if the hominins were living at such a high latitude (40�N) in warm or cold conditions. The latter would be of great interest as it suggests both the use of fire and clothing, and probably adaptation to cooked tubers. In fact, even in the current interglacial episode Beijing gets mighty cold in winter. However, cosmic-ray bombardment can produce unstable isotopes that are suited to dating in that gap, provided materials have been exposed to them. The fossil-containing sediments in Zhoukoudian Cave contain quartz that was exposed at the surface and washed in at the same time as H. erectus individuals were dragged in. Decay of cosmogenic ²⁶Al to ¹⁰Be and measurement of parent and daughter isotopes in quartz grains have yielded ages of 770+80 ka, somewhat older than earlier estimates (Shen, G. et al. 2009. Age of Zhoukoudian Homo erectus determined with ²⁶Al/¹⁰Be dating. Nature, v. 458, p. 198-200). This age roughly correlates with layers in the western Chinese windblown loess deposits that were deposited during the dry conditions of a minor glacial episode.
See also: Ciochon, R.L. & Bettis, E.A. 2009. Asian Homo erectus converges in time. Nature, v. 458, p.153-154. Gibbo0ns, A. 2009. Ice age no barrier to �Peking Man�. Science, v. 323, p. 1419.

Walking with the ancestors

From time to time the most evocative hominin trace fossils come to light, such as the Australopithecus afarensis footprints fount by Mary Leakey at Laetoli in Tanzania. A recent one is of footprints of a probable H. ergaster dating back to 1.5 Ma near Lake Turkana in Kenya, not far from the site of the famous �Turkana Boy� skeleton of the same species (Bennett, M.R. and 11 others 2009. Early hominin foot morphology based on 1.5-million-year old footprints from Ileret, Kenya. Science, v. 323, p. 1197-1201). Not only does the trackway reveal details of flesh, skin and bones of the feet, but careful analysis of 3-D scans of the prints, in the context of the mechanical properties of the material walked upon, allows the authors to show that the person who left them moved in essentially the same way as do we when walking through soft mud. They are distinctly different from the Laetoli prints, showing arches and very distinct big toes that are so necessary for �springiness� and bipedal balance respectively.
See also: Crompton, R.W. & Pataky, T.C. 2009. Stepping out. Science, v. 323, p. 1174-1175.

Deeper roots of culture

There has long been a pervasive aroma of eurocentrism in cultural palaeoanthropology, encouraged by the spectacular cave paintings in southern France and northern Spain that are no more than 40 ka in age and the first to be discovered. This undoubted flowering of art as we appreciate it today has been linked to much more than figurative expression. Some have argued that Homo sapiens only became fully human after Europe was colonised. Thankfully, the archaeological record is rapidly being set straight by more and more discoveries of symbolic representation from elsewhere (Balter, M. 2009. On the origin of art and symbolism. Science, v. 323, p. 709-711). Blomberg Cave In South Africa is a repository for 100 ka old inscribed ochre artefacts (Balter, M. 2009. Early start for human art? Ochre may revise timeline. Science, v. 323, p. 569), which represent symbolism of some kind and the imagined uses to which the ochre was put � ritual or cosmetic body painting? But there are tantalising objects that push art back even further. In 1999 a cache of stone tools at Tan-Tan in Morocco was found to include a 6 cm quartzite chunk that looks like a rough version of the �Aurignacian Venuses� of later times, yet the find dates back to 300 to 500 ka. Something similar turned up in the 250 ka site of Berekhat Ram in the Israeli-occupied Golan Heights of Syria. Both predate the evolution of fully modern humans. And what of the tear-drop shaped biface �axes� associated with H. erectus and H. ergaster as far back as 1.6 Ma? These are extremely odd objects, for several reasons: it is hard to visualise their use; many finds are in pristine condition, as if never used; to make one demands a mental model of what potentially lies within a rock; they are more difficult to make than later blade tools that are more utilitarian. Arguably, the �Acheulean hand axe� may be more of a symbol than a tool.

The reason for renewed discussion in print of these matters is, of course, the bicentenary of Charles Darwin�s birth and the 150th anniversary of publication of his Origin of Species. Darwin drew a link between tool making and language in his Descent of Man. He would have been delightedly surprised to learn details of the emergence of new tool-making skills in Africa, from where he insisted we all came (Morgan, L.E. & Renne, P.R. 2009. Diachronous dawn of Africa�s Middle Stone Age: New 40Ar/39Ar ages from the Ethiopian Rift. Geology, v. 36, p. 967-970). Morgan and Renne, of the University of California at Berkeley, discovered that the oldest sites in the Main Ethiopian Rift that contain the novel tools that mark the onset of the Middle Stone Age (MSA) span a much greater interval than assumed hitherto. In one site such tools date to 276 ka, whereas at another such objects appear only at 183 ka. The more delicate work to make MSA points and blades, and a much diversified �tool kit� has been called the Levallois technique, thought to have been associated with a cognitive leap from the Lower Palaeolithic Oldowan and Acheulean techniques. For some it came to signify more: the appearance of fully modern humans. But the new ages do not tally with the fossil record of H. sapiens or with estimates from mitochondrial DNA molecular clocks. All in all, culture, whether art or technology, seems to be characteristic of the genus Homo. Given a push bike, could H. ergaster have ridden it and, more important, had fun? What would a Neanderthal, male or female, have done with a tube of lipstick?

The Neanderthal genome is coming!

Some computer owners take part in the search for extraterrestrial intelligence, allowing SETI to combine their processing power with that of hundreds of others, on the off chance that the meaning of π (pi) pops up in a systematic burst of non-static microwaves. Personally I would far rather wait for a message from a relative than from some seriously weird being whose motives we might never guess. A Neanderthal lady � more precisely her leg bone �from Croatia is very close to speaking volumes about our own history. Two teams of DNA sequencers are putting the finishing touches to her genome. That it would ever happen was a fevered dream not so long ago. That it will opens up a revolution in understanding our origins. To keep in touch, read Elizabeth Pennisi�s account of the pending revelations (Pennisi, E. 2009. Tales of a prehistoric human genome. Science, v. 323, p. 866-871). Svante Paabo gave a glimpse of his team�s rough draft of the genome at the AAAS annual meeting in February 2009. When analyses are finished palaeoanthropology will explode onto the news channels, blogs, and among the twittering classes. Should SETI get a result, I would first eat my trousers and then prepare to be eaten myself. As for Darwin, maybe you have noticed his prominent brow ridges�

Technology, culture and migration in the Middle Palaeolithic of southern Africa

The period between 300 and 30 ka was critical for the evolution of modern humans. Our mitochondrial DNA indicates that fully modern humans emerged around 200 ka. Projectile weapons that help define the epoch first appeared. Clear signs of self-adornment and symbolism also turn up during the Middle Palaeolithic. All of these developments took place in Africa, and the last two are reflections of the increased efforts by archaeologists in the continent from which we all originated. There is a long way to go to match the density of sites from which later periods in human history have been outlined in Europe, but progress is accelerating. One great hindrance has been dating sites, for the Middle Palaeolithic lies in a time zone where the Ar-Ar and 14C methods are ineffective. A developing chronological �workhorse� for this difficult period depends on the way in which exposure of sand grains to sunlight �heals� the defects in their molecular structure formed when radioactive isotopes in soils emit ionising radiation. Artificial illumination of sand grains containing these defects causes them to luminesce. The degree of luminescence is related to the time over which the defects have built up. Optical dating relies on grains having been exposed at the surface for a time to �reset� the luminescence clock, and then being buried so that new defects can accumulate. Having lots of sunlight and a superabundance of bare sand, Australia has become a hotbed of research into optical dating of events associated with its peopling during the last ice age. Expertise developed there has been applied to many Middle Palaeolithic sites in Southern Africa (Jacobs, Z. et al. 2008. Ages for the Middle Stone Age of Southern Africa: Implications for human behaviour and dispersal. Science, v. 322, p. 733-735).

Archaeological work in South Africa and Namibia has revealed two distinct stone industries in the Middle Palaeolithic, both of which made hafted weapons that would have made hunting more efficient than the whatever weapons were used in earlier times � the most distinctive of the preceding Lower Palaeolithic tools was the bifacial hand axe, whose use is obscure. Both cultures involved the earliest recognisable ornamentation, such as shell beads and materials engraved with symbols, together with indirect evidence for the use of hematite and goethite pigments for body painting (see When and where �culture� began in EPN of November 2007). Genetic evidence famously places modern human origins and their global migration out of Africa within this time frame. So, dating the archaeological sites as accurately as possible is a crucial importance, and a tremendous start has been made by the multinational team lead by Zenobia Jacobs of the University of Woolangong in Australia. Optical ages span 90 to 30 ka, with clusters between 71.9 to 71 ka and 64.8 to 59.5 ka, with a statistically significant gap of about 6.7 thousand years between them. When compared with climatic-change indicators from the Antarctic ice record the developmental episodes do not seem to correlate clearly with any specific warm of cool periods, though the earlier spans the time of the Toba super-eruption in Indonesia and the later one was a period of warming. So any environmental cause for the technological and cultural changes is unclear. However, both fall within the estimated time span of the genetic �bottleneck� between 80 and 60 ka, and the most likely times for the initial �Out of Africa� migrations, probably across the Straits of Bab el Mandab linking Eritrea and Arabia across the Red Sea shallowed by ice-cap linked falls in global sea level.

Childhood and families

Human females are unlikely to break 10 seconds for the 100 metres because of their sashaying gait. It can�t be helped, being due to the evolution of the pelvic girdle of bipedal females to deal with birthing of infants with increasingly large heads. Supposedly, the human female pelvis is now close to the limit that will permit walking on two legs. Such problems do not plague other living primates partly because their young have small heads relative to their bulk, and pelvic anatomy is not constrained by an habitually upright gait. It seems not to have been an �issue� for australopithecines either: they did not possess �child-bearing hips�. The intermediate species, Homo erectus, despite having a 1 Ma fossil record (maybe as long as 1.8 Ma for the Asian form) only recently provided substantial pelvic remains (Simpson, S.W. et al. 2008. A female Homo erectus pelvis from Gona, Ethiopia. Science, v. 322, p. 1088-11092). In the words of the authors, this pelvis is �obstetrically capacious� and demonstrates that female skeletal evolution responded to increasing foetal brain size: it would have permitted infants with heads 30 to 50% of the adult size to have been born. Homo erectus has been widely supposed to have had a tall willowy frame analogous to that of fully modern human inhabitants of tropical savannahs, yet the Gona woman was stocky. So, environmental influences seem to have had less of an evolutionary role than the advantages of greater brain development before birth. That places H. erectus even more firmly on the human line; indeed greater in utero brain development seems to have taken place than in modern humans.

The Gona pelvis demands re-evaluation of how foetal and childhood development has progressed over the last two million years (Gibbons, A. 2008. The birth of childhood. Science, v. 322, p. 1040-1043), the unique attributes having appeared during the evolution of our own genus. Among chimpanzees, infants can fend for themselves, with a little help from elders, after 3 years old. Street children from Asia and South America need to be 6 before they can survive without parental care. Growth lines on teeth that appear week by week reveal that previous age estimates for a number of immature australopithecines whose first adult molars had erupted were large overestimates: instead of 6 they point to 4 years old. Another signal feature of human development is the lengthy period to full development (marked by the eruption of the 3rd molar as well as the end of significant growth in stature). The average age when human child bearing begins is around 19, while chimpanzees start at about 11. A fresh examination of the famous Turkana Boy�s skeleton, an H. erectus, that uses tooth microstructure reduces his age at death from 13 to 8, suggesting an earlier onset of independence than in modern children. He grew much more quickly too, and would have reached adulthood somewhat earlier: around 14.5 years old. The picture with Neanderthals is not completely clear, some tooth studies suggest that their children grew significantly more quickly than modern ones, other studies point to the same rates or even longer development if adult brain sizes of Neanderthals are taken into account (larger on average than those of modern humans). Using average life expectancy of gatherer-hunter humans and chimps who survive dependent childhood � 45 and 70 years respectively � along with evidence for child development, suggests that australopithecines could have reached 45 while H. erectus adults could have expected to reach 60 years old.

There are other differences that begin to slot into space with the new data. Both human and chimpanzee females have a similar child-bearing period of around 20-25 years. The difference is that, on average, the natural interval between births is about half as long for human mothers as for chimpanzees. The greater number of human offspring gives a greater chance of the survival of some to reproduce themselves. On the other hand, slower child development places a greater burden on mothers, even after weaning. So there is quite a contradiction between the evolutionary effects, if only child-mother relationships are taken into account. This contradiction was resolved, to some extent, by a seminal paper in the late 20th century by a group of anthropologists from the Universities of Utah and California (see O�Connell, J.F., Hawkes, K. & Blurton Jones, N.G. 1999. Grandmothering and the evolution of Homo erectus. Journal of Human Evolution, v. 36, p. 461-485). They focussed on the potentialities of the early onset of infertility or the menopause among women relative to its appearance among female chimpanzees, which gives, on average, a 30 year non-child-bearing period to older women. This approximately coincides not only with child-rearing periods for their daughters, but for their granddaughters as well. The �grandmothering� hypothesis for human development centres on the great evolutionary advantages of post menopausal women assisting with child rearing. O�Connell et al. suggested that this arose among H. erectus, as far back as 1.8 Ma, and the Gona pelvis together with other new views of H. erectus development add considerable weight to that concept. As well as freeing younger women for food gathering, the cultural significance of older women caring for children adds another dimension that may link to the advantages of delayed post-weaning development that we see today, albeit in many annoying contexts!

Early, microscopic evidence for human control of fire

Which human species first controlled and used fire has been debated for as long as archaeologists began to realise we had a long and complex ancestry. Because sites can easily be contaminated by charcoal from natural fires it has been difficult to present convincing evidence. But there is a way to get believable data. Stone tools and fragments from their manufacture may have fallen in fires set by hominins, and show changes caused by intense heating. One such example comes from a long-occupied site in Israel (Alperson-Afil, N. 2008. Continual fire-making by Hominins at Gesher Benot Ya�aqov, Israel. Quaternary Science Reviews, v. 27, p. 1733�1739). Nira Alperson-Afil of the Hebrew University of Jerusalem investigated small flint artefacts, probably flaked off during tool making, from eight levels excavated at the site. In all of them some flint shards showed signs of extreme heating, such as discoloration, crazing and tiny bowl-shaped pits (�potlids�) resulting from exfoliation of hot flint surfaces. The features are reproduced by experimental heating of flint shards, and do not occur in those that have not been heated above 300�C.

Gesher Benot Ya�aqov was first occupied around 790 ka, by Homo antecessor, and the excavation levels may span around 100 ka. The site is the earliest to provide convincing evidence not only for the use of fire, but that it was a continuous part of the hominins� culture: they could make it at will. Alperson-Afil suggests that fire making may have been an integral part of the Acheulean culture, well known for finely crafted biface axes, since its inception around 1.6 Ma ago. Ambiguous evidence for hominin fire use, such as burnt bones and reddened sediments, has been found at several sites in Africa dated between 1 and 1.5 Ma. Alperson-Afil�s meticulous micro-forensics should help African archaeologists and those working at very old sites left by migrating hominins in Georgia and Asia to check whether fire has such a long-lived place in our evolutionary history.

Return to �Doggerland�

Because sea levels rose world-wide after the last glacial maximum, archaeologists have been largely stymied as regards exactly where migrating people lived and what they did. Much migration since fully modern humans left Africa around 70-80 ka is likely to have been �strandloping� along coastal lowlands exposed as sea level fell as the last glacial period developed. Of course, this vast area is now drowned. It takes both a lot of work and a degree of good fortune to make anything of this landscape for ancient humans. Luck definitely played its part in getting some clue about one of the last of the migrations: from continental Europe to the British Isles, in the aftermath of the last glacial maximum. Trawlers have dredged not only animal bones from what was a great plain where the North Sea now sits, but also a superb bone harpoon point recovered in 1931. It has been a while in coming, but researchers at Birmingham University, UK have finally defined and mapped that drowned land area � Doggerland (see: Spinney, L. 2008. The lost world. Nature, v. 454, p. 151-153).

Dietary negation

The hominin genus Paranthropus rarely hits the front page by comparison with the related australopithecines, despite their having had jaw and cheek bones that would put Sandy Shaw and a variety of 60s catwalkers to shame. (It is only polite to observe that there the vague similarity ends, for paranthropoids have a bizarre skull crest attached to jaw muscles and brow ridges that were probably better than a baseball cap at preventing glare.) The first (P. boisei) to be unearthed at Olduvai, Tanzania in 1959, was dubbed �Nutcracker Man� by its finder Philip Tobias. Despite having formidable chewing tackle to drive its massive flat, thickly enamelled cheek teeth, wear on their surfaces is little different from that on the teeth of �gracile� australopithecines. (Ungar, P.S. et al. 2008. Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei. PLoS ONE, v. 3, on-line e2044 (www.plosone.org) doi:10.1371/journal.pone.0002044). They show no sign of the microscopic pitting that characterises teeth of living primates that eat hard, brittle foods, such as nuts or woody stems. Similar studies of the teeth of P. robustus show insufficient wear to suggest an habitual diet of that kind, although it may have eaten such foods when others were in short supply. Chances are that huge jaws and big teeth evolved to give paranthropoids a wider choice of diet and hence greater fitness in a climatically fluctuating terrain. It seems they chose to eat soft foods when available, as do gorillas today. In any event, they were remarkably successful creatures, and the two species cohabited the East African savannah with several human species, including H. erectus, for around a million years from 2.2 Ma when they appeared. Carbon-isotope data obtained from 20 paranthropoid and 25 australopithecine teeth by other researchers reveal a broad but similar diet for both, i.e. a mix of grasses and fruits, suggesting both had eating habits that could shift from apes to those of baboons. However, such C-isotope data cannot distinguish between exclusive vegetarianism and eating the flesh of herbivores. Low dental wear is also associated with meat eating�

See also: Gibbons, A. 2008. Australopithecus not much of a nutcracker. Science, v. 320, p. 608-609; part of a report on the April 2008 meeting of the American Association of Physical Anthropologists

Clovis First hypothesis dumped

For decades palaeoanthropology of the Americas has been dominated by a single idea; that nobody entered the continents before those people who used the elegant fluted spear blades first found near Clovis, New Mexico in the 1930s. These were eventually dated at a maximum age of around 13 ka before the present. One reason for accepting the Clovis people as the first Americans, apart from the lack of conclusive evidence for any earlier occupation, was the fact that glaciers blocked the route from the Bering land bridge of the last Ice age until about 13 ka. Increasing evidence has suggested earlier penetration by people who did not use Clovis tools from Asia, which reached Chile by around the same time and possibly as early as 33 ka. However, none of the evidence is definitive and the Clovis First hypothesis has been stoutly defended against this growing body of contrary evidence.

The ‘traditional’ idea of American occupation by humans after 13ka has taken a double whammy from an unusual set of fossils – of human excrement – discovered in a cave in Oregon. These have been dated at up to 15 ka and are unmistakably human, containing human mtDNA with genetic signatures typical of Native Americans (Waters, M.R. & Stafford, T.W., Jr. 2007. Redefining the Age of Clovis: Implications for the Peopling of the Americas. Science v. 315, p. 1122-1126; Gilbert, M.T.P et al. 2008. DNA from pre-Clovis human coprolites in Oregon, North America. Science, DOI:10.1126/science.1154116).

Ideas of how and when the Americas were colonised are changing rapidly after decades of ossification. A fascinating article in the 14 March 2008 issue of Science magazine reviews the issues and prospects (Goebel, E. et al. 2008. The late Pleistocene dispersal of modern humans in the Americas. Science, v. 319, p. 1497-1502). Genetic studies of living native Americans suggest their common ancestry in a Siberian population no earlier than 30 ka, and perhaps as late as 22 ka. The Beringia land bridge had repeatedly created a possible migration route during every major glaciation followed by many of the Pleistocene mammals that inhabited the Americas, but not by humans until the late stages of the last glaciation. Dating of archaeological sites and remains, including the human coprolites found by Waters and Stafford, is slowly pushing back the earliest evidence for a human presence to around 15 ka, several trhosand years before the Clovis culture appeared. Sometime before that, the first Americans had arrived and begun to spread. Ice barred their way through the interior of Alaska and NW Canada, and they must therefore have travelled along the coast, where the way was open from Beringia to Cape Horn; perhaps they used boats to move along the flat, but frigid shores of Beringia and the rugged western seaboard of North America. Early populations subsisting on shoreline resources would not have needed the heavy projectiles of the Clovis culture that are more attuned to ‘big-game’ hunting on plains. That may explain the sudden appearance of Clovis artefacts once access to plains was possible around 13.5 ka and its equally sudden disappearance at the start of the Younger Dryas around 12.8 ka when survival on icy plains would have become very difficult. Interestingly, the period of occupation of Siberia around 30 ka, would have presented the Beringia route to migration to North America when climate was similar to that following the last glacial maximum. So far, no tangible evidence

Homo floresiensis had big feet

Controversy has raged about her identity since the skull of a minute female hominin was unearthed from the Liang Bua cave on the Indonesian island of Flores. On the one hand are authorities who believe the fossil is that of a distinct human species, while on the other are sceptics convinced that the diminutive stature and chimp-like brain capacity reflect some pathological issue in a population of ordinary humans. The 12 April meeting of the American Association of Physical Anthropology in Columbus, Ohio (see Culotta, E. 2008. When hobbits (slowly) walked the Earth. Science, v. 320, p. 433-435) were treated to an anatomical exposition of the rest of the Liang Bua skeleton. A great deal more turns out to be different from human characteristics, including the legs and feet. Amusingly, for J.R.R. Tolkien’s Hobbit had them, the feet of H. floresiensis were disproportionately large. Also, her gait was quite different from ours – a kind of careful, high-stepping plod. Although not all agree, the post-cranial bones of H. floresiensis appear to bear close resemblance to those of early Homo species. Those favouring a separate species from our own suggest either that it arose through allopatric speciation from SE Asian H. erectus after isolation of a population on Flores, or perhaps even that it is a relic of an early migration of H. habilis from Africa almost 2 Ma ago. Whatever, it is now going to be even more difficult not to speak of hobbits.

Orrorin walked the walk

Orrorin tugenensis is one of those fossils over which palaeontologists tend get heated. It is a hominin, old (~6 Ma) and fragmentary, so it just might be the daddy of us all. That possibility takes a significant step forward with statistical evidence that Orrorin walked upright in a similar manner to the much later australopithecines and paranthropoids (Richmond, B.G. & Junggers, W.L. 2008. Orrorin tugenensis femoral morphology and the evolution of hominin bipedalism. Science, v, 319, p. 1662-1665). The study was made independently of the original discoverers, who claim that the femur has especially human-like features. Whichever, one of the original suggestions that Orrorin was on the ancestral line to gorillas has become improbable. The creature clearly displays the oldest known example of a bipedal gait (the older Sahelanthropus (~7 Ma) is known only from skull fragments and teeth, although its skull’s foramen magnum hints at bipedalism). In itself, Orrorin’s walking biomechanics is remarkable, as molecular evidence suggests that the branching that led to chimpanzees and to hominins is not much older than 6 Ma. It does seem as if that phylogenetic split may well have centred first on adaptation for traversing open ground from a forest common ancestor.

Colonisation of Europe pushed further back

Europe is so close to Africa that in recent years repeated waves of immigrants have crossed the Straits of Gibraltar, often on frighteningly flimsy craft. Their driving force is simply the search for a better life in the booming economies of Spain and Italy. Far more intense pressure from deteriorating climate and vanishing game drove Africans of many earlier times to escape their home continent, reaching back almost 2 million years. So how come the European hominin record is so short? At last count it went to H. antecessor around 750 ka, albeit a species that was sufficiently adventurous to reach British shores (see Earliest tourism in Northern Europe in EPN of January 2006). The famous Sierra de Atapuerca cave systems in northern Spain have now yielded clear evidence of much earlier occupants from around 1.1 to 1.2 Ma ago in the form of a lower jaw fragment in association with tools and bones showing signs of butchery (Carbonell, E. and 29 others 2008. The first hominin of Europe. Nature, v. 452, p. 465-469). Provisionally, the person has been assigned to H. antecessor, and there are two possible interpretations: either (s)he was a new immigrant from Africa, or represents a new speciation in northern Spain from an earlier population of African colonists. The paper’s title may prove to be premature.

A Cretaceous Ice Age?

Accepted geoscientific ‘wisdom’ is that the Cretaceous Period was so warm that forests reached polar latitudes and so too did cold-blooded reptiles. Planktonic foram oxygen isotopes indicate that the Cretaceous ‘hothouse’ in the Turonian (93.5-89.3 Ma) produced tropical sea-surface temperatures up to 37°C; warmer than human blood temperature. It also saw sea level reach an all time high. Both features have been attributed to the rate of ocean-floor volcanism being at its highest. It has, however, been difficult to model the warmth at high latitudes without fudging the input to general circulation models.

Measuring d18O in both planktonic and benthonic (ocean-floor) forams at centimetre spacings in Turonian ocean-floor sediments seems to have truly bamboozled specialists in the Cretaceous. They reveal a period of ~200 ka at around 91.2 Ma where both show a sharp increase (Bornemann, A. and 8 others 2008. Isotopic evidence for glaciation during the Cretaceous supergreenhouse. Science, v. 319, p. 189-192). Respectively, the peaks reflect decreased sea-surface temperature (but only down to 32°C in the tropics) and an increase in the extraction of light 16O from the oceans; only likely when ice caps build up on land. The size of the benthonic d18O increase suggests ice caps about half the size of that now blanketing Antarctica. Other evidence includes rapid decreases in Turonian sea level in Europe, North America and Russia; only likely on such a scale as a result of glacio-eustasy. However, direct evidence in the form of tillites, striated pavements and glacio-marine sediments has yet to turn up

Until these convincing data emerged, it seemed that sufficient post-Permian frigidity for large-scale glaciation had not developed until Oligocene times. However, the paradox of high-latitude ice caps and low-latitude balmy seas is resolvable. Evaporation from the tropical sea surface would have been much greater than nowadays. Transport of moisture to cooler areas may have resulted in such immense winter snowfall at high latitudes that sufficient remained unmelted after winter darkness for its albedo to further cool the polar region. Almost certainly the site for the ice cap would have been Antarctica, which in the Cretaceous, as now, sat over the South Pole. Remove the present ice, and that continent would have had an average surface height of between 1 and 2 km that would have encouraged snow build up were sufficient to have fallen during the Turonian. Yet without the direct evidence for glaciation in sediments – much would be buried by the present Antarctic ice cap, if not eroded away - the scenario is difficult for some to believe.

Holocene cold spell and glacial lake burst

The most startling event during the gradual warming after the last glacial maximum was the millennium of icy conditions between 12.5 and 11.5 ka; the Younger Dryas. Long after Holocene warmth seemed well established and agriculture had been underway for two millennia, with perhaps increased human population, a smaller cold ‘snap’ took place, between 8.21 and 8.17 ka; i.e. for about 70 years. Its main effect was around the North Atlantic, but it was felt over the whole hemisphere. It must have been devastating for early farmers and new migrants into higher latitude lands. High-resolution records of many kinds are possible for such a young event, from both ice and marine cores, and also terrestrial pollen records. Norwegian, French and Dutch climate researchers have gleaned a great deal from a sea-floor core from between southern Greenland and Labrador (Kleiven, H.F. et al. 2008. Reduced North Atlantic deep water and the glacial Lake Agassiz outburst. Science, v. 319, p. 60-64). Their combined fossil, oxygen-isotope and mineralogical study shows anomalies from about 170 years before to 100 years after the drop in regional temperatures. These include signs of decreased saltiness of the water in the Labrador Basin and a reduction in production of deep water in the North Atlantic. This is exactly the predicted signature for a shut-down of the Gulf Stream, similar to those implicated in Dansgaard-Oeschger events through the last Ice Age and the Younger Dryas itself.

The Younger Dryas has been linked to sudden drainage of huge glacially dammed lakes that once surrounded the ice cap of the Canadian Shield. One scenario for that is a huge, protracted flood down the St Lawrence River into the North Atlantic, another being one down the MacKenzie River into the Arctic Ocean. Freshening of surface waters by such means would have reduced the formation of the dense cold brines that sink to form North Atlantic Deep Water today. In so doing these down-wellings drag surface waters northwards from low latitudes to form the Gulf Stream that makes the western side of the North Atlantic unusually warm. If they stop or slow significantly regional air temperatures fall, as they did again around 8.2 ka. In this case the likely cause was escape of water melted from the last dregs of the North American ice sheet that had been held in a glacial lake south of Hudson Bay: Lake Agassiz.

Neanderthals more ‘human’ than once thought

Sébastien Chabal, the gigantic and hairy back-row forward in the 2007 French World Cup rugby team, was nicknamed ‘The Caveman’ by French fans. Indeed he is an awesome spectacle, at almost 2 m tall and weighing over a tenth of a tonne, with great black beard and locks. But is seems that Neanderthals were redheads and probably prone to sunburn (Lalueza-Fox, C. and 16 others. 2007. A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals. Science, v. 318, p, 1453-1455). The team analysed DNA extracted from Neanderthal bones from Spain and Italy, and identified the mc1r gene that regulates pigmentation in many mammals. In both specimens it turned out to be a variant that is associated with fair skin and red hair. An artist has rendered a French Neanderthal man’s physiognomy from his skull, by combining this information with modern facial reconstruction techniques (in Culotta, E. 2007. Ancient DNA reveals Neandertals with red hair, fair complexions. Science, v. 318, p. 546-547). He seems set to become a pin-up among those ladies who favour the larger gentleman, even having a nose far larger than that of Gerard Depardieu. Although proof of the growing power of genetic analysis of ancient tissue, that Neanderthals were probably pale-skinned is not really surprising. They inhabited high latitudes for at least 200 ka longer than modern Europeans have, and the pale variant of mc1r is advantageous where sunlight is at a premium for creating vitamin D. Like modern Europeans, their immediate ancestors who migrated northwards were almost certainly dark-skinned.

Yet by far the most scientifically exciting outcome of the team’s work is the extraction from the Spanish Neanderthal bones of the FOXP2 gene, which is implicated in the development of speech and language (Krause, J. and 12 others 2007. The derived FOXP2 variant of modern humans was shared with Neandertals. Current Biology, v. 17, p. 1908-1912). It shares two mutations with FOXP2 in modern humans, that had previously been suggested only to have developed in the last 100 ka, so must have been present in the last common ancestor of fully modern humans and Neanderthals, around 300 to 400 ka. Although this discovery cannot prove that Neanderthals spoke, taken along with emerging evidence that symbolic skills were used by even earlier hominins (see When and where ‘culture’ began in November 2007 issue of EPN) it does suggest they were capable of as much sophistication as the earliest fully modern humans.

Is human evolution speeding up?

Another outcome of the acceleration in genetic analysis is an ability to scan vast numbers of differences in DNA from many individuals. Highly productive are single nucleotide polymorphisms or SNPs (‘snips’) that are available from the international HapMap project. From analysing almost 4 million SNPs from 270 individuals has emerged an intriguing parallel between human population explosion since about 40 ka and an increasing rate at which new genetic traits have been incorporated into the human genome (Hawks, J. et al. 2007. Recent acceleration of human adaptive evolution.Proceedings of the National Academy of Sciences, v. 104, p. 20753-20758). The link is not entirely surprising, for the exposure of more individuals to mutagenic factors will result in more mutations entering the total gene pool. Yet ‘weeding-out’ of unfavourable mutations also operates over time, so the fact that around 7 % of human genes seem to have changed over the last 40 ka, indicates the overall rate of human evolution must have speeded up remarkably. The analysis suggests that the rate rose to a peak between 5000 and 8000 years ago, for Europeans and West Africans respectively. ‘Received wisdom’ has for a long while been that fully modern humans went through a phenomenal spurt in evolution around 50 to 40 ka (but see When and where ‘culture’ began in November 2007 issue of EPN), and that somewhat Eurocentric view is overturned by the SNP evidence. Selection pressures must have risen to a peak around the time of the spread of agriculture and the rise of large social communities – big changes in diet and in exposure to communicable disease would be associated with those shifts.

In some respects the findings are cause for optimism. Global warming and rapid transformation of climate belts will expose billions of people to new experiences. Hundreds of millions, or more, may perish, yet our species’ evolution may speed up again. Let’s hope it leads to some improvement in avoiding self-induced misfortune.

See also: Holzman, D. 2007. How we adapted to a modern world. New Scientist, v. 196, 15 Dec 2007 issue, p. 8-9.

Now we can celebrate the �Hobbits�!

It’s official: Homo floresiensis is a distinct hominin species from ourselves, and is not a pathologically affected human as some anthropologists would demand. The definitive feature lies in the Indonesian fossils’ hand bones, specifically those of the wrist (Tocheri, M.W. and 9 others 2007. The primitive wrist of Homo floresiensis and its implications for hominin evolution. Science, v. 317, p. 1743-1745). Three well-preserved wrist bones (the trapezoid, scaphoid and capitate) occur in the holotype specimen from the Lian Bua Cave on Flores. Human and Neanderthal wrists share very much the same shapes of these bones, whereas earlier hominin wrist bones are distinctively different, and more like those of other living primates. The Homo floresiensis wrist clearly falls in the second category. Because the wrist bones develop early in the primate embryo, differences are unlikely to have arisen through some kind of pathological disorder.

The discovery opens far more than a new human species (one that cohabited Flores with fully modern humans until 18 thousand years ago, and perhaps more recently). The ancestors of H. floresiensis migrated out of Africa before the evolution of the last common ancestor of humans and Neanderthals; at least 800 thousand years ago. The other long-term inhabitants of Asia were members of the H. erectus species, but so far no hand bones of theirs have turned up in the fossil localities of Java and China. Another candidate may be the hominins found at Dmanisi in Georgia, that date back to 1.8 Ma, for which some have hinted at a relationship with the earliest species of human, H. habilis. The holotype H. floresiensis is so young that there is a chance that DNA fragments may be discovered, to be compared with ours and those of Neanderthals; a truly exciting prospect.

When and where �culture� began

There is a deeply entrenched view that shortly after fully modern humans entered Europe they experienced an evolutionary leap that made them artists of supreme talent and inventors of tools the world had never seen before, and they may have begun to speak properly. There is no denying the beauty of late Palaeolithic cave paintings in France and Spain, nor the ingenuity of tools of that period found in European sites. Yet it has always seemed that to give them special significance is deeply offensive to people from elsewhere who descended from ancestors that were anatomically and genetically identical to European forebears. It has begun to seem more likely that the sudden appearance of art and improved technology in Europe resulted from colonisation of Europe by artists and inventors, who brought older talents from elsewhere. Probably the first ‘canvas’ used by artists was the human body, painting designs we can only guess at with iron oxide and hydroxide ochres. Indeed, common finds in archaeological sites are pieces of these minerals showing clear signs of having been worked, even some which look suspiciously like body-paint pencils. The oldest come from a sea cave in South Africa, and show groves produced by grinding. The deposits containing them are four times older than the artwork of Europe, around 165 ka (Marean, C.W. and 13 others 2007. Early human use of marine resources and pigment in South Africa during the Middle Pleistocene. Nature, v. 449, p. 905-908). The people were beachcombers at a time when sea-level was low during the beginnings of the last glacial period but one. The Mossel Bay cave is just the oldest repository of clear ochre painting materials, others being common through Africa and the Middle East in the period before Africans migrated to colonise the rest of the world. There are disputed examples of pigments more than 400 ka old from Zambia. But possibly the most startling, for Eurocentrist anthropologists is the so-called ‘Venus of Tan-Tan’ from Morocco dated between 300 to 500 ka, and similar figurines from Israel that are almost as old.

See also: McBrearty, S & Stringer, C. 2007. The coast in colour. Nature, v. 449, p. 793-794.

Migrations summarised

Fully modern humans are not unique in their history of colonisation of the world. Journeys out of Africa began as early as 1.8 Ma ago by the precursors of Homo erectus, to reach central China and Indonesia. Homo antecessor reached Europe by 800 ka at the latest, and there are earlier finds of tools in southern Europe. Our immediate ancestors spread throughout Africa and into the Levant by 100 ka, but the decisive move that eventually colonised every continent except Antarctica and most oceanic islands seems to have got underway at around 80 ka, when Africa was beginning to dry as global climate cooled towards conditions of the last glacial period. None of the huge peregrinations are likely to have been by design, but more a diffusion as conditions changed, food sources shifted and obvious opportunities presented themselves. A great deal of palaeoanthropology focuses on charting those migrations, using tangible signs of ancient people and their dates and positions, knowledge of geography, climate and feasible routes, and lately the spread of genetic markers found in modern human DNA samples.

In a rapidly moving field, summaries of the latest ideas are handy (Jones, D. 2007. Going global. New Scientist, v. 196 (27 October 2007), p. 36-41). In this case however, claims are made by the publisher for fundamental novelty (the article is headlined as “Humanity’s greatest journey: Tracing a new route out of Africa”). The suggested novelty is that our ancestors’ initial forays away from home were along shorelines as beachcombers, and the leap to Eurasia was across the Straits of Bab el Mandab between modern Eritrea and Yemen when the shallow southern Red Sea was almost dry during a glacial advance in the far north. There is nothing new in either. Jonathon Kingdon in Self-Made Man and His Undoing (1993) first suggested “Strandloping”. In Stepping Stones (1999) I speculated that the Straits of Bab el Mandab would have been an available exit from Africa for hominins using shoreline food resources at several times since 2 Ma. Stephen Oppenheimer argued in 2003 for that route having been used at around 85 ka, backed up by strong fossil evidence for established beachcombing on the coast of Eritrea. His seminal book Out of Eden (2003), was the first systematic attempt to draw together tangible evidence with all the available genetic threads and their dating to reconstruct a coherent picture of human migrations. There is a fascinating web site on the course of human migration, authored by Oppenheimer, at www.bradshawfoundation.com/journey.

In the same vein is a summary of a conference in Cambridge, UK, which focused on an integral aspect of global migration: evidence for seafaring (Balter, M. 2007. In search of the world’s most ancient mariners. Science, v, 318, p. 388-389). That people did cross wide stretches of sea that are too deep for sea-level change to make any difference is well established, particularly for eastern Indonesia, New Guinea and Australia. The now established ancient status of H. floresiensis (see above) supports much earlier seafaring by hominins. The question is: did people set out deliberately aboard some kind of craft, or were early crossings accidental, as is the case for other land animals, presumably on drifting vegetation? The earliest known boats – hollowed logs from about 10 ka – are not exactly seaworthy for anything but coastal ventures. SE Asia is blessed, however, by bamboo, whose flotation seems likely to have been exploited for near-shore fishing or journeys to fringing reefs at low tide. Were groups of people on bamboo rafts blown out to sea, prevailing monsoon winds could have carried them eastwards to new lands in a matter of days. To found new and long-lasting human bands would require at least 5 to 10 females and males to have been swept from their home shores. Sea-level rise since the time of decisive human migrations has, unfortunately, drowned any coastal sites of that time and evidence of when new beachcombing cultures became established.

The long reach of the Neanderthals

Neanderthals, at their acme, were widespread in Europe and the Levant, but new analyses of mtDNA from old bones in Uzbekistan and Siberia show their range to extend to about 90°E (Krause, J. and 9 others 2007. Neanderthals in central Asia and Siberia. Nature, v. 449, p. 902-904). The range is not one encouraged by warmer climates, for the Siberian bones are dated at about 38 ka, when northern Eurasia was caught in the grip of cold temperatures descending to the last glacial maximum. But there is evidence which suggests that climate change did play a part in the Neanderthal’s demise. Intricate and precise time series of climatic shifts, such as that from the Cariaco Basin off Venezuela, offer an opportunity to check out links between climate and the fate or otherwise of human populations; provided that evidence for the latter is abundant and well-dated. A cave in Gibraltar has yielded good evidence that suggests habitation by H. neanderthalensis in three periods: 32.5; 26.4 and as late as 24.0 ka (Tzedakis, P.C. et al. 2007. Placing late Neanderthals in a climatic context. Nature, v. 449, p. 206-208). The three dates correspond with periods of relative warmth, separated by cooling in the period of climate instability leading to the last glacial maximum. From the correlation it is hard to argue for a major role of climate change in Neanderthal extinction, merely that they favoured the location during easier times.

Georgian hominins; who were they?

Steadily, the numbers of fossils of early members of the genus Homo are accumulating to fill the period since 2-2.5 Ma when tools first appear in the archaeological record. The problem is that most are skull fragments that may suggest different species, but not a great deal about their owners behaved. Near-complete postcranial (body) fossils are rare: ‘Lucy’ (~3.5 Ma, A. afarensis) and Nariokotome ‘Boy’ (~1.6 Ma, H. ergaster) were the only ones for periods before the emergence of our immediate ancestors in Africa considerably less than 1 Ma ago. The earliest well-preserved migrants into Eurasia appear in ~1.8 Ma deposits at Dmanisi in Georgia, first found as head fossils and now partial postcranial ones have been described (Lordkipanidze, D. and 17 others 2007. Postcranial evidence from early Homo from Dmanisi, Geogia. Nature, v. 449, p. 305-310) from 3 adults and a single adolescent.

On the basis of cranial evidence alone, the Georgian hominins seem extremely primitive, their brain volumes being less than 800 cc, comparable with African H. habilis, and significantly less than H. ergaster and Asian H. erectus. Postcranial bones show they were diminutive, at around 1.5 m and 45 kg, but give a mix of ‘modern’ and ‘primitive’ features, such as a high leg:arm length proportion and an anatomical inability to throw over-arm, respectively. The latter is shared with H. floresiensis (see Hobbit matters, June 2006 issue of EPN), as is body size and brain volume. The absence of postcranial material from H. erectus poses a problem in assigning the Georgian hominins to that species, although Lordkipanidze and colleagues reckon they are early versions of that species. The bones missing for proper comparison with well-established (if not well-defined) species also open up the possibility that they are H. habilis, and even that they are the ancestors of H. floresiensis. If that was the case then they were remarkably successful in Asia (but also very good at hiding, for no comparable fossils have been found except on Flores). While early hominin species are almost all defined on cranial fossils, for obvious practical reasons, the more finds are made that expand the diversity of forms, the more puzzling early human evolution becomes. That applies equally to Africa in the 2 to 1 Ma period, a ~1.6 Ma Kenyan skull, assigned by some to H. erectus is much smaller than that of roughly contemporary Nariokotome ‘Boy’.

See also: Lieberman, D.E. 2007. Homing in on early Homo. Nature, v. 449, p. 291-292. Gibbons, A. 2007. A new body of evidence fleshes out Homo erectus. Science, v. 317, p. 1664.

Physiognomy and human origins

Compared with genetic comparison among living human populations, physiological variations in human anatomical collections have been almost completely overlooked as a means of assessing relatedness. That is not really surprising because of physical anthropology’s past, much tainted by deliberate racist inferences from measured differences. Lately, human morphometry has been used in a non-racist way to test the ‘multiregional’ hypothesis for the evolution of fully modern humans, a new analysis of variations in the human phenotype having appeared recently (Manica, A. et al. 2007. The effect of ancient population bottlenecks on human phenotypic variation. Nature, v. 448, p. 346-348). The new data present strong support for an African origin and global migration from that continent. The study, conducted at the University of Cambridge, UK and Saga Medical School, Japan used measurements from almost five thousand male human skulls less than 2 ka old, and a statistical methodology similar to that used in genetic studies. Around one fifth to a quarter of all the observed variation correlates with distance from Africa. Overall, the authors conclude migration from an origin in central to southern Africa, with no sign of any second place of origin. The results tally extremely closely with those based on purely genetic variability.

Earliest gorilla tags hominoid phylogeny

Understandably, the central focus on ape evolution has been on the branch that led ultimately to humans. That is traceable through fossils, possibly to between 6 to 7 Ma with the remains of Sahelanthropus tchadensis. From a genetic, molecular standpoint the branching to humans was from an ancestor shared with chimpanzees, previously dated by ‘molecular clock’ methods to around 6-7 Ma as well. By the same reckoning, an earlier ancestor, common to both and shared with gorillas, lived around 8 Ma. These branchings seem to have occurred in Africa during the Upper Miocene; a time not well-represented by sedimentary rocks and fossils in East Africa. Approaching a true phylogeny must rest on both molecular data from living organisms and on the anatomy of fossils, whose age can help calibrate molecular clocks. Newly found fossils from Afar in Ethiopia (Suwa, G. et al. 2007. A new species of great ape from the late Miocene epoch in Ethiopia. Nature, v. 448, p. 921-924) appear to demand a revision of the timescale of evolution among the great apes (Hominoidea). They seems to be from an ancestral gorilla. The Japanese-Ethiopian team found a single canine and eight partial molar teeth from 3 to 6 individual apes (Chorapithecus abyssinicus) in the oldest sedimentary rocks to have been deposited in the Afar Rift. The teeth are remarkably similar to those of modern gorillas. Although some primate specialists dispute the link to gorillas, were it to be demonstrably acceptable the discovery would push back the molecular timing, because the age of the sediments is between 10 to 10.5 Ma; 2 Ma before the estimated age of the gorilla-chimp-human last common ancestor. That branching would have been before 10-10.5 Ma, suggesting that the rate of mutation on which previous estimates were made was slower than had been calculated. The implication for the crucial hominin-chimp split is that it may have been as early as 9 Ma, giving more time for the emergence of bipedalism and many other hominin characteristics in Sahelanthropus and the closely following Orrorin and Ardepithecus.

Upright posture far older than hominins?

It is widely accepted that the hallmark of humans and their immediate ancestors is their upright posture and bipedal gait. Gorillas and chimps knuckle-walk, but humans do not. Consequently, palaeoanthropologists have always sought evidence, such as the site where the skull attaches to the spine (the foramen magnum), before placing fossils on the way to becoming human. Yet fossils far older than the 5-7 Ma span of accepted hominins and genetic evidence of the split between them and chimps are turning up with clear signs of upstanding habits. Interestingly, orang-utans often stand upright when climbing, despite being the large ape with the least liking for terra firma (Thorpe, S.K.S. et al. 2007. Origin of human bipedalism as an adaptation for locomotion on flexible branches. Science, v. 316, p. 1328-1331). They do it on slender branches, holding other branches for support, because if they tried a quadripedal gait, the branch would likely snap.

Orang-utans are a lot more distant genetically from humans than are chimps and gorillas, to the extent that their last common ancestor with humans would have lived in the Miocene, about 15 Ma ago. Thorpe et al. offer the fascinating possibility that being bipedal in trees was a great advantage to early apes, and that gorillas and chimps lost it while hominins retained that ancient trait. Close examination of how orang-utans get around in trees presents remarkable similarities to human locomotion on the ground: they react to flexible branches very like humans running on springy ground, whereas other primates do the opposite.

See also: O’Higgins P. & Elton, S. 2007. Walking on trees. Science, v. 316, p. 1292-1294.

No interbreeding with Neanderthals

In the January 2007 issue of EPN (Neanderthal genome on the cards) I reported there a possibility that we might have some Neanderthal genes. Breaking news in Science (Pennisi, E. 2007. No sex please, we’re Neandertals. Science, v. 316, p. 967) suggests not. The Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, in its push to sequence the genome of a Croatian Neanderthal fossil, has data on nuclear DNA that pushes back the time of the last common ancestor with humans from around 500-600 ka to 800 ka, and finds no evidence of gene flow between the two species.

Climate change and palaeoclimatology

Magmatic link to the Palaeocene-Eocene warming

The abrupt 5° C global temperature rise at the Palaeocene-Eocene boundary around 56 Ma ago stemmed from massive release of methane, probably from gas-hydrates on the sea floor. What triggered that blurt is not so well constrained, although the development of the North Atlantic large igneous province has long been suspected, as flood basalts in Greenland and northern Britain have about the same age. The North Atlantic LIP involved between 5-10 million km³ of magma, much residing beneath the continental margins, and was associated with the opening of the northernmost Atlantic Ocean.

The Palaeocene-Eocene methane release is recorded in sea-floor sediments by a sharp decrease in the proportion of ¹³C in carbonates within ocean-floor sediment cores. Magnetostratigraphy suggests that the release lasted only for about 20 ka at the start of around 210 ka of warming. Such a short duration is a challenge for establishing a precise absolute age and a linkage to any possible causes. In the Western Approaches to the English Channel a core contains a volcanic ash layer just above the carbon-isotope anomaly, as a target for precise dating (Storey, M. et al. 2007. Paleocene-Eocene thermal maximum and the opening of the northeast Atlantic. Science, v. 316, p. 587-589), to match with igneous events in the LIP. A total of 50 Ar-Ar total-fusion ages shows that this ash and a tuff high in the East Greenland flood basalts are statistically identical in age (55.12±0.09 Ma). This and other considerations virtually prove that the methane release coincided with the LIP. However, it remains to be established whether the link was through volcanically induced warming that destabilised submarine gas-hydrates or direct triggering of the greenhouse-gas exhalation. The ages fall within error of the age of continental break-up itself. Because vast areas of the rifted margins contain sills emplaced in the LIP, the authors suggest that the release was due to thermal metamorphism of carbon-rich sediments at the new tectonic margin; i.e. the released gas may have been CO₂.

See also: Kerr, R.A. 2007. Humongous eruptions linked to dramatic environmental changes. Science, v. 316, p. 527.

Whizz-bang view of Younger Dryas

News is beginning to break of a potential controversy to rank with that surrounding the K-T boundary event (Dalton, R. 2007. Blast in the past. Nature, v. 447, p. 256-257; Kerr, R.A. 2007. Mammoth-killer impact gets mixed reception from Earth Scientists). At the May AGU meeting in Acapulco, Mexico, two dozen scientists presented evidence to suggest that the sudden cooling at 12.9 ka that led to the Younger Dryas millennium followed upper atmosphere explosions of cometary material. The usual signs are said to be around: excess iridium; spherules; fullerenes and evidence for huge wildfires. They seem to lie directly above the last known occurrences of the superbly crafted spear and arrowheads known as Clovis points, which are the hallmark of the earliest known humans in North America. The YD seems to have finished off the mammoths as well, if they hadn’t already been eaten by the Clovis hunters.

Short-lived events, no matter how massive, seem unlikely to have created conditions for thousand-year ‘nuclear winters’ forced by dust blocking solar irradiation. The loose consortium involved in the discovery suggests that an air-burst by exploding debris from a comet melted part of the remaining Laurentian ice sheet. That would have caused a surge of fresh water into either the Arctic or North Atlantic Oceans to disrupt Gulf Stream circulation—the original model by Broeker, but ascribed by him and others to breaching of ice dams to proglacial lakes. The impact concept has been gathering followers for several years. But it has been attracting many critics too, not least because among the consortium are scientists who produced similar evidence for an end-Permian impact, that has never been independently reproduced since. The more excitable are scouring satellite images of North America for signs of actual impact sites that may be of the same age—for instance a series of elliptical depressions known as the Carolina Bays of eastern USA. But, the idea resurrects an old hypothesis about mammoths. Not only are mammoths found in Siberian permafrost with flesh that can be eaten, if a little gamey for some tastes, but their stomachs contain barely digested grasses and flowers. It was once suggested that the mammoths were flash-frozen by extremely cold air from the upper atmosphere that rushed down in the aftermath of some kind of volcanic or impact-induced blast.

Do Neanderthals sit next to us on the train?

Many might answer, �Yes, and they speak loudly about their love lives into mobile phones�, but that is a tired old joke. A much better one is that related by Steve Jones of University College, London. Were an unwashed but shell-suited, Late Palaeolithic, fully human hunter-gatherer to sit next to us, we would probably change seats. Jones believes that if our companion turned out to be a freshly showered, shaved and eau de cologned Neanderthal in a business suit, we would change trains. Neanderthals were impressive, in the manner of all-in wrestlers with extremely large noses and eyebrows.

A boy�s skeleton turned up in Portuguese 24 ka cave deposits in the late 1990s. The lad had the hallmark chin of a modern human but the stocky body and short legs of a Neanderthal. He may be the only tangible evidence of a human inter-species hybrid. There again, he may have been a perfectly normal, stocky boy with short legs. Yet the find re-opened the possibility that Neanderthal genes may have made their way into modern humans. It certainly does not look like it from the available DNA fragments extracted from Neanderthal bones, but ongoing attempts to sequence the Neanderthal genome (see Neanderthal genome on the cards in January 2007 EPN) could resolve the issue. But the ambitious genetic plans have sent a thrill through scientific journalists with palaeoanthropological leanings (Jones, D. 2007. The Neanderthal within. New Scientist, v. 193 (3 March 2007), p. 2832).

Another skull claimed to show hybrid features has turned up in Romania, but the most tantalising hints come from existing knowledge of human genetics. The Out of Africa model for all modern humans is based on studies of mtDNA and that from Y chromosomes, which now enable human migrations to be tracked and put into a time frame. But such genetic material forms a tiny proportion of the human genome. It is nuclear DNA that dominates and is also responsible for how we function and how we look. There is so much of it that work has only just begun in the context of human origins. One haplotype, in the PDHA1 gene, has shown up something odd in a small sample of men from different continents. Two lineages seem to be represented, one that a molecular clock dates to a last common ancestor 1.8 Ma ago [Homo habilis?], the other having split at about 200 ka. That duality should not be present if all living people descended from a small group who lived around 160 ka. Either it resurrects the almost-buried multiregional model, or points to occasional interbreeding with other human species that our forebears encountered: only time and a lot of work will tell. Yet fertile offspring must have emerged from such liasons. In a Linnaean sense that implies that however the partners might have looked and whatever their habits were, they had to have been the same species: one that had lasted almost 2 million years in different guises or polymorphs, as Jonathon Kingdon once suggested.

Anthropology and geoarchaeology

Other rich hominin pickings

Yes, it seems thay they did...

Neanderthal �bling�

Evidence for early journeys from Africa to Asia

Fungal clue to fate of North American megafauna

Early hominin takes over Science magazine

Fire and tool making

Neanderthals few on the ground

Klondike gold rush pays dividends for Pleistocene

African genes

Very old human footprints in Mexico?

�Hobbit� news

Flirting with hand axes

Homo erectus in a cold climate

Walking with the ancestors

Deeper roots of culture

The Neanderthal genome is coming!

Technology, culture and migration in the Middle Palaeolithic of southern Africa

Childhood and families

Early, microscopic evidence for human control of fire

Return to �Doggerland�

Dietary negation

Clovis First hypothesis dumped

Homo floresiensis had big feet

Orrorin walked the walk

Colonisation of Europe pushed further back

A Cretaceous Ice Age?

Holocene cold spell and glacial lake burst

Neanderthals more ‘human’ than once thought

Is human evolution speeding up?

Now we can celebrate the �Hobbits�!

When and where �culture� began

Migrations summarised

The long reach of the Neanderthals

Georgian hominins; who were they?

Physiognomy and human origins

Earliest gorilla tags hominoid phylogeny

Upright posture far older than hominins?

No interbreeding with Neanderthals

Climate change and palaeoclimatology

Magmatic link to the Palaeocene-Eocene warming

Whizz-bang view of Younger Dryas

Do Neanderthals sit next to us on the train?

More primate genes

Out of Africa, with an ulcer

Neanderthal genome on the cards

The diet of robust australopithecines

Back to Africa

`Peace' (Selam) disturbed

Drying East Africa

Asian migrations reviewed

Out of Africa and back again?

Implications of a mismatch between hominin genes and bones

Hobbit Matters

Hominid evolution: a line or a bush?

Palaeodentistry

Asian Homo erectus skilled in tool making

Climate change and collapse of early civilisations

Culture and Human Evolution

Earliest tourism in northern Europe

Biogeochemical evidence for vegetation change when hominins evolved

The geological sources of myths

Congenital disease, human migration and population growth

Growing evidence for `hobbits'

Climate change and human evolution

Has human evolution stopped?

Caring among the Erects

Changing the World

Did the earliest agriculture kick-start global warming

The oldest modern humans

Interbreeding: louse study leads to head scratching

Jared Diamond on the Flores "hobbits"

Neanderthals vs moderns: how come we won?

SA discovery that will run and run?

Something to chew over

The perils of genealogy

Anthropological nit picking

The little people of Flores, Indonesia

The earliest granny factor