Fossil genomics is opening new windows to the past. But the view through them isn't as clear as we like to think
Illustration by Richard Wilkinson
Jonathan Marks is professor of anthropology at the University of North Carolina at Charlotte. He wrote The Alternative Introduction to Biological Anthropology (2011).
Neanderthals hold a special place — biologically and mythologically — in the knowledge of who we are and where we came from. Even now, scientists cannot agree whether they are a variant of our species, or a separate species in our genus Homo. The discovery of Neanderthals in the 19th century pointed to a deep history of ‘otherness’ in Europe, of people who might have been ancestors, variants, or even victims of modern-day Europeans. Their differences from us are fairly small. You can find people today with brow ridges, or sloping foreheads, or weak chins, or long heads, or narrow faces, or projecting mid-faces, or large jaws with more than enough room for the wisdom teeth. But you don’t find those features together, or quite so extreme, in anyone living today. The discovery of remnant ‘Neanderthal genes’ in modern Europeans has rekindled the debate about how we make scientific and cultural sense of our human ancestry — and, more broadly, of our place in the natural order of things.
What, then, is our relation to the Neanderthals? Are ‘they’ the odd-looking people whom ‘we’ — that is to say, lanky, round-headed, anatomically modern Homo sapiens — dispossessed and exterminated? That was an explanation that made sense to 19th-century Europeans, who imagined their own colonial ambitions and barbaric exterminations stretching back into the dim past. Or did ‘they’ represent humans in a state of pure nature, their lives ‘nasty, brutish and short’ as Thomas Hobbes and his Enlightenment successors portrayed the forerunner — and shadow — of civil society? Perhaps ‘they’ were neither primordial victims nor primordial forebears, but simply freaks of nature — deformed, maybe by accident of birth or circumstance of life, and interesting because they are weird and pathological?
The truth is likely to be ‘a little of each’, since the alternatives were never mutually exclusive. Their bones show lots of evidence of healed fractures; their teeth are worn as if they were being used as tools; and their muscular development was strikingly asymmetrical. Whatever they did, it was rigorous, it was cultural and it was humane (at least, they took care of friends with broken arms better than chimpanzees do). They also tended to get a lot more exercise on one side than the other. They were replaced in the fossil record of Europe by less stocky people like you and me, who had chins and foreheads. And yes, they were ‘uncivilised’. They often buried their dead, but never sent any grave goods along with the deceased for the journey. They didn’t build anything, or at least anything lasting or recognisable. If they decorated themselves, or had any aesthetic sensibility at all, it was rudimentary at best.
On the other hand, their contemporaries, (some would say simply our ancestors) — people with chins and foreheads, whom you think of as being familiar because you, too, have a chin and forehead — also led rigorous lives almost unimaginably different from your own. For most of their existence, they lived without writing or the wheel, without crops or tame animals, without metal, matches, or even fish-hooks. If you were transported into their world, you wouldn’t last five minutes without them to help and teach you. We have to realise that they were in fact not much like us at all. A simple two-part classification between our ancestors and the Neanderthals is based on an unlikely set of biological criteria that would have made little sense at the time, and makes even less sense now when we consider the murky genetics at work.
When we pruriently inquire whether the Neanderthals and our own kind could have interbred, we are assuming rather a lot about the composition of those two groups. Just because foreheads and chins are important to our classification systems, there is no reason to think that people 100,000 years ago would have seen you and thought, ‘Hey, there goes another one of us forehead-and-chin guys’. More likely, they would have regarded you as at least as alien as a Neanderthal, based on the criteria we generally use for such assessments: what you’re wearing, how you’re groomed, whether you can communicate sensibly and can behave properly.
In other words, we tend to use cultural criteria to sort who belongs where. Do you really associate only with people whose head shapes resemble yours? Of course not; you associate with people who tend to speak like you, dress like you, and share your general interests. You’ve probably never even taken note of their foreheads, much less made decisions about them on that basis.
Why did they become extinct? Too dumb, too uncommunicative, too carnivorous, too cold-adapted, too pacifist, too conservative, just too damn ugly?
This gets to the fundamental problem in dealing with our ancestry: we make sense of the Neanderthals by seeing them in distinctively cultural ways. We imagine that, because we scientists juxtapose ourselves against them anatomically, people in the Late Pleistocene must have done the same, although that goes against what we know of modern human behavior.
Not only do we impose modern cultural ideas upon their life, but on their death, too. The most frequent question we ask about the Neanderthals is: why did they become extinct? Why didn’t they make it, as we did? As framed, the question invites you to identify the flaw in Neanderthals, why they missed out on ‘the preservation of favoured races in the struggle for life’ as Darwin’s subtitle to On The Origin of Species had it. What, in short, was wrong with them? In addition, we have quite a list of candidate flaws: too dumb, too uncommunicative, too carnivorous, too cold-adapted, too pacifist, too conservative, just too damn ugly.
And yet we don’t ask that question about other former human groups. What was wrong with the Hittites? What was wrong with the Gauls? What was wrong with the Sumerians? What was wrong with the Olmec? If they had empires, their empires rose and fell. But we see the people themselves as part of the ebb and flow of human bio-culturally constituted social units — assuming identities, having identities imposed upon them, leaving their graves and objects behind, and having descendants with other identities and other ancestors.
It’s hard not to think of the Neanderthals as a cohesive unit, different from ‘us’ and aware of it, and behaving accordingly. But it is probably a mistake to constrain our understandings of Pleistocene peoples by encoding our own cultural biases into them.
Biological anthropology occupies an interesting intellectual space between the study of how heredity works (human genetics and evolution) on the one hand, and how groups of people think and act (traditionally cultural anthropology) on the other. By its nature, it takes an inter-disciplinary focus on the diversity and ancestry of our own species. The difference between biology and biological anthropology lies in reflexivity. Biological anthropology breaks down the distinction between subject and object that is so fundamental to science. One simply cannot have the same relationship to ancestors and neighbours as one has to hydrogen or fruit flies.
So how do we study ourselves effectively? There are two options. One is to pretend not to be human at all. Actually, Thomas Huxley came up with this trope in Evidence as to Man’s Place in Nature (1863) — the very first book on human evolution. He wanted to convince his Victorian readers that they ought to be classified with the apes, based on the anatomical similarities to apes, rather than be swayed by the obvious differences from the apes. Since we are both different from, and similar to, the apes, we can reasonably choose to emphasise either relationship. So Huxley reached into his rhetorical bag of tricks, and invited his readers to imagine themselves as ‘scientific Saturnians’. Such wise scientists, who could be objective about human attributes, since they themselves came from elsewhere in the solar system, would no doubt agree with Huxley and classify us with the apes.
But, if you want to be more objective about studying humans, there are two problems with this approach. First, there are no systematists on Saturn, and consequently we haven’t the faintest idea what an alien systematist would do to classify us. In 1926, the biologist Henry Fairfield Osborn said that a Martian would classify human races into different species and genera; in 1992, the biologist Jared Diamond said that a Martian might classify our entire species as a form of chimpanzee. The other problem is that we know human beings have very diverse ways of classifying the living world. An extra-terrestrial systematist might not classify us as we’d expect at all. Perhaps they would divide us up by how we taste.
In short, this argument confuses science fiction with science, and begins by denying the one fact that is unimpeachable here — that we are humans classifying humans
The second approach to overcoming our human biases is to accept the fact that the subject-object distinction here is blurry, and that the study of human ancestry and diversity cannot be a science like fruit fly biology — where the subject (the scientist) has no problem establishing intellectual distance from the object (the fly). The challenge then becomes to understand the conflicting interests that go into the science of ourselves, and not to take it at face value. It might be a less familiar, more humanistic kind of science, but it’s better science than pretending that you are a Martian. In fact, a good rule of thumb is: anybody who claims to be as objective as an alien about the study of humans is probably too naive to be trusted.
To understand our place in some sort of natural evolutionary order, we must first begin by sorting the fossils we have into meaningful units. This isn’t as easy as it sounds, and is the subject of bitter and longstanding professional feuds in paleontology. For example, Tim White, the distinguished paleoanthropologist and professor of integrative biology at the University of California, Berkeley, reviewed a book called The Last Human (2007) with this stinging rebuke:
This is all part of hominid ‘diversity systematics’ run amok. Many of the putative species are chronotaxa; others are not even valid species in that sense. No one really thinks that available hominid fossils represent 22 separate species lineages in the last 6 million years.
But obviously the authors of the book thought so: its subtitle is A Guide to 22 Species of Extinct Humans, and in it they argue that they can discern, in the human fossil record over the past 6 or 7 million years, 22 distinct species — with 12 of them in the genus Homo, just in the past 2.5 million years.
We sometimes describe this as the tensions between ‘splitting’– the tendency to focus on the differences between specimens and argue there are many species – and its opposite, ‘lumping’. These may seem to be capricious practices of shuffling the relevant fossils into lots of small piles or into a few big piles. And woebetide the ‘splitter’ whose book is reviewed by a ‘lumper’! But this isn’t capricious at all. It is strategic. After all, more species means more key specimens, which makes a greater number of museums important and more scientists important too. Cladistic analysis, the most basic analyses of human fossils, assumes that similarities are generally inherited over time from a shared ancestor, rather than transmitted horizontally by admixture between groups – and the best way to make that assumption ring true is to see fossils as species, rather than as subspecies, which could mix. On top of this, there are nationalistic rivalries for claiming the most important hominin fossils. Whose fossils hold the key to understanding our origins – the species from Kenya (Homo rudolfensis), South Africa (Australopithecus sediba), Georgia (Homo georgicus), or Spain (Homo antecessor)? Or is it ‘all of the above’?
What is more, there is such pressure on scientists to name new species – whether justified or not – that many biological areas are experiencing ‘taxonomic inflation’ – the formal recognition of way more species than are really there. This is particularly rampant in our closest relatives, the primates, where the number of recognized species has more than doubled in the last twenty years. It is not as if a great many new species have been hiding from view in the interior of Madagascar or the Amazon rainforest, and have only recently been encountered. Nor is it true that primates are experiencing extraordinarily rapid rates of speciation. The reason that there are twice as many primate species as there used to be is that many of them are endangered, and conservation legislation is often written to protect species. The legal status and protection of primates in the wild is consequently helped by making them species (rather than, say, making them subspecies or local populations). Here the decision is that the conservation needs of the primates are the most important factor. And who would presume to disagree, aside from a heartless pedant?
But as Tim White’s book review indicated, we ought to take these classifications with a pinch of salt. We are studying ourselves, our ancestors, and our relatives. And we do it in a cultural matrix of conflicting interests and values – all with the eventual goal of telling us who we are and where we come from, which is itself invariably highly politicized knowledge.
Modern genomics might be a good place to turn for new data to help us understand our relationship to earlier populations. Unfortunately, modern genomics always seems to be selling something. Whether the product is a cure for genetic disease, or your very own DNA sequence, or the secrets of your ancestry, the transformation of the previous generation’s genetics into modern genomics has awakened the entrepreneurial spirit. The problem is that the entrepreneurial spirit likes to make promises which the data can’t deliver. After all, the Human Genome Project promised a cure for diseases, but that hasn’t come. Your genome is loaded with statistical associations to all kinds of health risks, but the information comes from a ‘direct-to-consumer’ company without the personal mediation of a genetic counsellor to help make sense of them for you. And commercial tests of your genetic ancestry can be so weird that they come with the disclaimer ‘recreational’.
Consider this product: the website Africanancestry.com can match your African-American mitochondrial DNA against a large sample of Africans and tell you where your African ancestors came from. But due to the poor sampling of that vast continent, the non-specific nature of the DNA matches, and the fact that mtDNA (inherited from your mother’s mother’s ... mother) identifies fewer than 0.1 per cent of your ancestors back in 1700, or 12 generations ago — the answer you get might have little or no biological meaning. Its value lies in the cultural meaning, and in the presentation of hi-tech genomic data as conferring validity upon that meaning.
Or look at this product: the website Rootsforreal.com can match your Y-chromosome DNA against those of Jews who self-identify as ‘Cohanim’ (or priests descended from Aaron the brother of Moses) and see if you belong to their hereditary caste. But look at the historical assumptions involved — that the story told in Exodus is reasonably true, that the Jewish priesthood is descended intact from a person named Aaron, who actually had a brother named Moses, that the 19 generations separating Moses from biblical Adam are less true than the rest of the story, and that the pattern of Jewish Y-chromosomes does not have a more mundane explanation involving population structure and inbreeding. Still, wouldn’t it be cool to know? And people will pay hundreds to find out. Biomedical science has long been commodifying the human body, as Rebecca Skloot’s bestselling book on the history of medical science, The Immortal Life of Henrietta Lacks (2010), illustrated. It is not too difficult to see the commodification of the body’s ancestors by genomics as an extension of that practice.
Is that a problem? Not necessarily; it’s just not the way we were taught to think about science. Genomics is one of the most vigorous sciences bearing on contemporary anthropology, since its conclusions deal with the fundamental questions of human ancestry and heredity. But if the British chemist and novelist CP Snow was right, and science constitutes a kind of ‘culture’, then it stands to reason that anthropology would be particularly valuable in understanding science, especially a science that brings an authoritative voice to something as culturally meaningful as our own ancestry and descent.
Genomics fundamentally reinforces what we already knew about Neanderthals from the fossil record: they were very much like us, yet slightly out of the range of modern human variation. However, the most interesting conclusions genomics provokes are about the three-way relationship between the Neanderthal genome, the modern human gene pool, and the Siberian contemporaries of both.
The methodologies used in genomics are cutting-edge, both technologically (in extracting and sequencing the DNA of 60,000-year-old fossils) and statistically (in comparing long DNA sequences and making sense of the patterns of similarity and difference). Yet the real information that can be extracted from these impressive technical achievements is very limited. The gene pool of Europeans even 10,000 years ago is an alien one to modern Europeans. We like to imagine ourselves in our ancestors’ place, perhaps, transcending time through a common genetic heritage, but that is just a charming illusion. Many of us would not have even been able to converse with our ancestors just a few centuries ago; they would be more exotic to us than the Samoans were to the anthropologist Margaret Mead in the 1920s.
The study of descent and kinship is actually far more interesting and complex than geneticists seem to realise
We imagine our ancestral trees spreading out into the past, each generation doubling. But a moment’s reflection shows that this is physically impossible. Assuming that a human generation is about 25 years, and that every ancestor had two parents, how many ancestors did you have 10,000 years (or 400 generations) ago? The answer is 2400, or 2.58 x 10120, or, for the sake of this discussion, a squijillion. That is many more orders of magnitude than the number of people who were actually alive at the end of the Upper Paleolithic, 10,000 years ago, or today for that matter. The only way this is possible is that all humans are, to some extent, inbred and all 7.1 billion (109 or 1010) of us share those squijillion ancestors — indeed, a recent statistical study in Nature found that the human gene pool could have coalesced as recently as 5,000 years ago. The millions of people alive back then are all our common ancestors; what differs among us is how frequently each of those ancestors recurs in our specific lineages. In other words, as recently as, say, 10,000 years ago there are no qualitative differences in any of our ancestries, only quantitative differences.
So what might we expect to find when we look at 60,000-year-old DNA samples and start comparing them to living humans? A very confused picture, I would guess. An ancient population might be a lineal ancestral pool of a modern one. Alternatively, they might just share genes with the modern population due to introgression or because they are a remote, non-specific source of ancestry both for ‘us’ and for any other comparable population. Statistically, these options can be formally distinguished from one another. Historically? I’m not so sure.
The picture has been considerably complicated by the discovery of the ‘Denisovans’. Supposedly, these were a once-mighty race of hunters who looked the dreaded woolly mammoth in the eye without flinching, and braved the harsh winter of the Asian steppe with steely resolve. Actually, all we know of ‘them’ is two teeth and a girl’s pinky, found in a cave in the Altai mountains of Siberia in 2008, and analysed at the Max Planck Institute for Evolutionary Anthropology in Leipzig. The little finger’s mitochondrial DNA showed it to be different from both Neanderthals and humans; its nuclear DNA seems to place it as a divergent offshoot of the Neanderthals.
What is interesting about the Denisovans is that their traces of descent are not found in the genomes of people who live in or around Siberia, but rather, in Oceania. So prehistoric Siberians are linked to modern New Guineans; prehistoric Europeans are linked to various Eurasian peoples and, in a related study, modern Africans are associated with a heretofore unknown prehistoric genetic stock. In each case, the amount of linkage to the archaic group is significantly less than 10 per cent of the genome. Each of these pockets of ancient genes are interpreted as being the result of acts of prehistoric miscegenation, of interbreeding.
What might all this mean?
I think it means rather less than it seems. As with the fossil data, the interpretation of the genomic data is rife with contradictions. Nowadays, the Neanderthals are brandished either as evidence for the ‘multi-regional’ hypothesis of human evolution — that modern people are descended from those Middle Pleistocene people who lived in their geographical area, a theory supported by a small bit of Neanderthal DNA in modern genomes. Or they are seen to support the ‘out-of-Africa’ hypothesis — the alternative view that modern people are descended just from Middle Pleistocene Africans, a theory also supported by a small bit of Neanderthal DNA in modern genomes. In other words, it hasn’t really resolved anything.
The problem, I think, is a failure to think clearly about what we are doing when we reconstruct categories of ancient people in the light of our own interests. In the late 19th century, the linguist Max Müller abstracted a group he called ‘Aryans’ from the inferred ancestral Indo-European language. After all, there had to be somebody speaking the language. He eventually came to regret having so reified them, because there wasn’t any evidence that they existed at all. My feeling is that the Denisovans are a reification as well, built from genetic data, biological deduction, and anthropological assumption. We commonly acknowledge the biological assumptions that go into the scientific calculations — things such as the mutation rate, generation time, population sizes, and degrees of contact with other populations — but we rarely confront the anthropological ones — that is the assumptions about what human groups are and how they work.
People group themselves, and are in turn grouped by others, after all, in all kinds of ways. This is true inside science as well as outside it. A Neanderthal is identified on the basis of anatomy; a Denisovan on the basis of genetics. To what extent are those categories even comparable to one another? Geneticists tend to take their populations as ‘natural’ units in a way that troubles anthropologists. That is why you can find a linguistic group (such as Bantu) contrasted against a political state (French) and an ethnic label (Druze) in the same genetic study, without any awareness that they refer to entirely different kinds of belonging. When geneticists have queried the construction of their samples, they tend to place an uncomfortable emphasis on ‘purity of ancestry’, denying the realities of human history, with all its murky interbreeding and complexity. Looking for admixture, after all, presupposes a primordial state without it.
The study of descent and kinship is actually far more interesting and complex than many geneticists seem to realise, for it is fundamentally a bio-cultural affair, for which genetics provides only one kind of clue. As Mark Jobling, professor of genetics at the University of Leicester, complained in the Philosophical Transactions of the Royal Society in March:
Geneticists who observe a pattern in their data and seek an explanation for it tend to visit a library, take out a history book and read about a past event that seems to explain the pattern they see. This kind of historical cherry-picking leads to a lack of objectivity in asking what kinds of past events could have given rise to modern genetic diversity.
Human ancestry is actually not just a question of genetics; it is a highly inter-disciplinary question and it needs to take account of the multiple ways that human beings count themselves to be inside or outside of different groups, and different identities. Biology is but a part of this picture.
In sum, there will always be an answer to be found in the data, but it can only be as good as the question that frames it. And I’m not sure how good the questions that are being asked of the data are these days. In the history of science it’s common to discover that the ‘natural’ and the ‘cultural’ have been co-producing one another. Surveying the ways in which genetics has engaged with the anthropological concept of ‘race’ over the last century, for example, shows that geneticists have consistently been able to find race when they think it is supposed to be there, and to lose it when they don’t. Results that are so subtle (your DNA is, say, 2.3 per cent Neanderthal), self-contradictory (Denisovan girl is both a variant Neanderthal and not a variant Neanderthal), and odd (modern New Guineans are uniquely descended from prehistoric Siberians) may entail more cultural than biological sense-making. Indeed, what we are dealing with here is how people think about themselves in relation to one another and to their ancestors. It is kinship: the oldest research program in anthropology and still as important as ever if we are to make sense of our place in the world.
21 November 2012