22.12.2011

What made us human

Simon Wells reviews Chris Stringer 'The origin of our species' Allen Lane, 2011, pp333,

Professor Chris Stringer of the Natural History Museum is one of the world’s leading experts on human fossils, famous for advancing the ‘recent African origin’ (RAO) model. The origin of our species, a semi-autobiographical account, describes how human origins research has developed. As he explains in the introduction, “I want to try and provide a comprehensive - but comprehensible - account of the origin of our species from my position in these debates over the last 30 years or so” (p1). Nobody interested in human origins should do without this book.

Its nine chapters range over archaeology, fossil specimens, life history, DNA, language and symbolism to the future evolution of the human species. Some of these subjects may seem daunting to the uninitiated, with terms and concepts unfamiliar to those seeking an introductory text. However, each chapter is clear and concise, the terms are explained, and the reader comes away having learnt something.

Stringer aims to address the big questions about what made us human. His wide-ranging interdisciplinary approach is impressive. Obviously, his knowledge is greatest in addressing the fossils with which he has worked so closely, augmented by his up-to-date grasp of relevant developments in molecular genetics. When it comes to questions of language and symbolism, discussing archaeological evidence on possible ritual and religious activity, he is probably weakest, lacking a social anthropology background. But his treatment of data and models is always meticulous, as he explains them all clearly and dispassionately.

The problem for any scientist in this area is to discern how new discoveries add to our understanding and enable us to pose questions to guide future research. One of the most interesting chapters, ‘What lies beneath’, looks at techniques applied to teeth, including computerised tomography - CT scans. The most modern and minute versions of CT scans require subatomic particle accelerators, such as the synchrotron at Grenoble. This is now revealing fascinating differences in the childhood of modern humans compared with Neanderthals, who appear to have grown up at a faster rate.

Comparing Neanderthals with modern humans has always been at the heart of Stringer’s work, since his PhD is from the early 1970s, right at the beginning of multivariate computer analysis of fossils. To get his data, he trundled around museums from west to east of Europe as a long-haired hippy in an old banger. Luckily, the long hair and unkempt beard got him across the Czech border to measure some important fossils at Brno; the guards relented about denying him entry, as he reminded them of Che Guevara!

Through this foot-slogging, detailed work examining far-flung specimens, Stringer became certain that Neanderthals were not ancestral to Europeans, whether Cro-Magnons or people today. Fossil evidence accumulating from Africa led him to develop his ‘out of Africa’ stance by the early 1980s, when it was highly controversial. The ensuing battle between adherents of the multiregional and RAO models caused a rift in the palaeontological community, with Stringer and colleagues emerging victorious.

Besides the fossils, the new molecular genetic studies from the 1980s onwards gave almost unequivocal backing to RAO. Mitochondrial DNA (mtDNA), found outside the nucleus of cells and inherited through females only, shows that the common ancestor of all humans living today - so-called ‘African Eve’ - is less than 150,000 years old. Since diversity of mtDNA lineages is greater in Africa than the rest of the planet put together, her homeland was definitely Africa.

The original ‘African Eve’ results of Cann, Stoneking and Wilson have stood up surprisingly well. In this book, Stringer examines closely how the RAO model measures up to the latest exciting genetic evidence on both Neanderthals and the even more mysterious Denisovans. Analysis of mtDNA from a Siberian fossil little finger (dating 40,000 years at present) shows that it is neither modern human nor Neanderthal, with a time span of separation reaching back 500,000 years. There are shared genetic links with Melanesian peoples. If you are European or Asian, about two per cent more of your DNA is shared with Neanderthals than if you are African. This suggests a model of some interbreeding perhaps 60,000 years ago in the Middle East, as modern humans exited Africa. Stringer claims that he never absolutely ruled out some mating going on between these populations, and he concedes the picture of our origin is shown to be more complex.

But, whatever genetic sequences have come down to us today, marking out population movement and migration, genes in themselves explain nothing. To answer the question of what made us human, we need to understand the behavioural selection pressures, or other factors, which led to those genes being the ones that made it. For instance, Forkhead box protein P2 genes (FOXP2) may determine ability to coordinate certain facial muscles, without which speech cannot work. But FOXP2’s presence or absence tells us nothing about the Darwinian selection pressures leading to language.

To get at that, we need to engage in modelling hominin social and sexual lives. Stringer, as one of the original authors of The human revolution with Paul Mellars, has never been afraid to look at social arguments. He gives a solid overview of the archaeological evidence that has been piling up in Africa (and the Middle East) over the past decade, indicating symbolic activity and challenging the Eurocentric idea of the Upper Palaeolithic as the main stage of the human symbolic revolution. He outlines the positions that various archaeologists have now adopted in response to the African record, and the debate about defining modern behaviour. These run from The revolution that wasn’t of Alison Brooks and Sally McBrearty, through the D’Errico/Zilhão ‘multispecies’ account of comparable Neanderthal symbolic activity, to the Henshilwood ‘symbolic organisation’ watershed of the modern human species, and the last-ditch defence by Richard Klein of genetic mutations making a sudden cognitive change about 50,000 years ago.

Because the African evidence on regular pigment (red ochre) use now ties in so well with the dates for modern speciation, it is a little surprising that Stringer does not seize on this with both hands to say yes to the human revolution in that 150,000-year timeframe. All the previous problems of explaining why we have modern anatomy at that early date in Africa, while apparently no symbolic activity till much later in Europe, have now been resolved.

Instead, he inclines to the rather fiddly version of Robin Dunbar’s ‘social brain’ hypothesis, arguing for incremental levels of intentionality. Each clause here represents one of those: ‘I believe that you think that John did something bad which god knows about and will punish him for’, representing steps from basic theory of mind to full-scale belief in the supernatural, forming a basis for moral values. Stringer gives a fair account of how this ‘levels of intentionality’ argument has been practically applied to increasing elaboration of symbolic practice in the archaeological record, notably by Paul Pettit.

While this may sound perfectly sensible from a bourgeois, individualistic perspective, any classic social anthropology text on ritual experience - Durkheim, Rappaport or Victor Turner - rips apart this flimsy house of cards. Ritual does not do understanding of ‘I think you said he did this or that’. Ritual does ‘we’: ‘we are here’, ‘we belong to god!’, and it is the only possible medium for generating that. It is the engine of what Michael Tomasello calls ‘collective intentionality’. Placing collective intentionality in charge was surely the essence of the human revolution. What revolution reflects only ‘a low level of symbolic intent’? A revolution is a ground-breaking event, transforming and turning the world upside down. The preoccupation with incremental levels of intentionality risks missing this point. There are no different levels of intent. What counts is only one intention: Revolution!

This theoretical dispute underlies the debate about whether red ochre in the archaeological record indicates symbolism. According to Pettit, who would certainly not claim to know much about anthropology or even the pigment record, smears of pigment have no more significance than trying to show off one’s rosy cheeks. Using ochre on the body somehow does not count as symbolic by comparison with carving marks into ochre, or stringing tick shells together. The trouble is, Stringer has not well represented the counterargument to all this, best made by Ian Watts, the major expert on the African Middle Stone Age pigment record. Watts has assiduously examined the colour selection and dating on regular and ubiquitous pigment use in the southern African record to argue that it marks a ritual tradition. Yet all his thorough, anthropologically informed arguments have been airbrushed out here.

Stringer pulls his biggest rabbit out of the hat in the last chapter with his very personal account of the story of the Kabwe or Broken Hill skull - in some ways a leitmotif of his whole life. He vividly remembers seeing it (or a cast) as a boy in the Natural History Museum; the first important human fossil from Africa, it now resides outside his office. It was dug out from a Zambian ore mine in 1921, and with the destruction of the site, all hope of dating the fossil accurately seemed to be long gone. Enigmatic and primitive, Kabwe combines a close-to-modern brain size with a low forehead, massive browridges and sharply angled back of the skull, almost Homo erectus-like, a strange puncture wound, and abscessing. While old estimates often placed Kabwe around 300,000 years, many have argued it could be a more distant ancestor, even more than half a million years old. Fifteen years of detective work with colleagues at the Natural History Museum have produced a new estimate which is quite startling: Kabwe could be closer to 200,000 than 300,000 years. That would put it within a few tens of thousands of years of the first modern human, now recognised as the Omo Kibish 1 skull from Ethiopia, approximately 195,000 years old.

The lesson is that Africa, a vast continent encompassing virtually all of our recent evolutionary ancestry, contains yet unknown degrees of diversity. At the same time that modern humans were emerging, they would have lived in landscapes alongside more archaic populations, possibly into very recent times. This implies also that at least some of the traces of archaic genetic markers still found in people today may have arisen as a result of intermixing of archaic and modern populations within Africa, rather than interbreeding of ‘pristine’ modern people with archaic populations only after leaving Africa.

Despite its subject matter, this book is far from intimidating, and written in a relaxed style full of anecdotes, while referencing cutting-edge research. Unfortunately, the dim and dark illustrations are not on a par with the lavish presentation in Stringer’s previous volumes, Homo Britannicus and The complete world of human evolution (with colleague Peter Andrews).

This review was first published in Radical Anthropology No5, November 2011