Earth-Pages Archive News, Anthropology

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

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?