The Little Species that Could: Boivin et al.’s "Human dispersal across diverse environments of Asia during the Upper Pleistocene"

The environmental fluctuations that characterized the Pleistocene meant there were sometimes more- and sometimes less-attractive times for our ancestors and fossil relations to have left Africa for greener pastures. In their Jan. 15, 2013 electronic release, Nicole Boivin and her co-authors leverage their [nearly] unique knowledge of Arabia and southern Asian to try out an argument that they abstract in this way:

Fossil, archaeological and genetic findings are seen to converge around a consensus view that a single population of H. sapiens exited Africa sometime around 60 thousand years ago (ka), and rapidly reached Australia by following a coastal dispersal corridor. … We argue that the fossil and archaeological records are too incomplete, the coastal route too problematic, and recent genomic evidence too incompatible for researchers not to remain fully open to other hypotheses. … Current archaeological, genetic and fossil data … appear to increasingly favour a more complex out of Africa scenario involving multiple exits, varying terrestrial routes, a sub-divided African source population, slower progress to Australia, and a degree of interbreeding with archaic varieties of Homo. (Boivin, N., et al., “Human dispersal across diverse environments of Asia during the Upper Pleistocene.” Quaternary International (2013),  

So, what can Boivin et al. tell us about our evolution that we didn’t already know? Their paper gives us a possibility, not a likelihood. It accommodates some data. It tells a story.

To the great pleasure of this reader the authors present some stunning graphics of the range of palaeoenvironments across Africa and Asia in the Pleistocene [see below]. These help to underscore their main contention that at different times during the Pleistocene, environmental conditions were changing such that anatomically modern bipedal apes would have had numerous opportunities to spread beyond Africa and into Asia. In that nutshell is, I think, the fundamental problem with Boivin et al. That’s because, rather that supporting their arguments, the archaeological record as it stands is telling us that the anatomically modern version of Homo sapiens, extant between about 195 and 40 kyr ago, was little better at adapting to new environments than an African bovid.

In the two maps shown below I’ve melded each of the four maps in the paper so as to produce a panorama of the pertinent geography at MIS 5 and 4.

MIS 5—Interglacial conditions between about 130 ka and about 71 ka. From Boivin et al. 2013.
MIS 4—Mainly glacial conditions from about 71 ka to about 60 ka. From Boivin et al. 2013.

During MIS 5, the authors point out, a continuous, hominid-friendly, environment spanned northeastern Africa, the southern Arabian peninsula, and southern Asia. In other words, Nature afforded H. sapiens a ‘way out’ of Africa during MIS 5. By contrast, in MIS 4, that same part of the globe was covered in red—i.e. not a nice place for hominids. So, no hominids got out. In so doing [IMHO] the authors paint a picture of a species that was so niche-specific as to be incapable of any kind of rapid adaptation to new environmental conditions. In none of the discussion do Boivin et al. appear to realize the apparent behavioural rigidity their model proposes as characterizing early anatomically modern H. sapiens. Indeed, their model stands in stark contrast [it seems to me] to the almost infinite behavioural plasticity that we’ve grown accustomed to hearing about whenever someone is listing the hallmark manifestation of we modern humans. Boivin et al. are begging the question “Were they human like us?”

By adopting this posture toward H. sapiens, the authors shoot themselves in the foot. Indeed, they appear to be arguing for a reduced set of ‘cultural adaptations’ prior to the time that people like us first set foot in southwestern Asia about 40 or 50 kyr ago. The more recent H. sapiens had a recognizably modern set of abilities, and it is those H. sapiens that, in a geological blink of an eye, spread across Asia and into Australia [the actual duration of the spread may have been on the order of 5,000 years]. What’s more, the behaviourally modern H. sapiens did so by changing gears whenever they encountered a novel ecosystem. Think of it. If Boivin et al.’s vision of H. sapiens’s capacities is anywhere near accurate they’d have a hard time explaining the persistence of the Inuit or the Tierra del Fuegans, both of which groups have managed to survive in, without doubt, the harshest conditions on Earth.

Overall, I’m incredibly happy to accept Boivin et al.’s portrait of the environments in marine isotope stages 4 and 5, the interglacial/glacial swing during which Homo sapiens arose in Africa, i.e. somewhere between about 190 ka and about 160 ka. From that time until about 40 to 50 kyr ago the authors aver that Homo sapiens didn’t just pop out once, but did so numerous times, following different pathways, and biomes.

All along the archaeological world had been aware of two excursions by H. sapiens out of Africa—one about 100 ka and the other at 40 to 50 ka. The authors propose that it may not have been as simple as the archaeological and record might have us believe, and that there may have been at least one more and possibly many more excursions out of Africa that are, at present, archaeologically invisible. Getting back to observations for the moment. At around 100 ka we see anatomically modern Homo sapiens at Qafzeh Cave in what’s now Israel. At that time H. sapiens was evincing the same behaviours as those of their contemporaries, the Neanderthals, which were distributed across Europe and into Central Asia. And here the authors’ idea runs out of gas, by not recognizing the possibility that, anatomical similarities notwithstanding, the two excursions could easily have been undertaken by two behaviourally very different flavours of H. sapiens. It has to be admitted that the Qafzeh H. sapiens at 100 ka was not acting as if they were people like us. They were, instead, behaviourally just like good Neanderthals—e.g. the same, Mousterian, behaviour with respect to working stone. Moreover, the Qafzeh hominids arrived in the Levant along with an African fauna, all of which appear to adhere to Boivin et al.’s model for expansion. But those earlier H. sapiens got no further, apparently, than that environment allowed. Because, by the time the environment had returned to glacial conditions, the Neaderthals were inhabiting the same geographic place that had been held by the Qafzeh hominids for at least 40,000 years previously. It appears, then, that the Neanderthals were associated with a western Asian faunal community. Thus, we have a picture of two species, acting in similar ways, each constrained by different environmental conditions. I’m sorry. That just doesn’t sound to me like they were much like us.

I’m not fond of nothing buttery. However, I see no other conclusion to be made but that anatomically modern bipedal apes at 100 ka were not cognitively similar to you and me, and thus couldn’t adapt to the transition from interglacial to glacial conditions. The authors state that many have called the dispersal of H. sapiens into the Levant around 100 kyr ago ‘failed.’ In fact they thrived for at least 40 kyr in the Levant in just the same way as they had done since arising in Africa—perhaps almost 200 kyr ago—and exploiting an almost identical environment to that which supported them in the Levant from about 100 kyr to about 60 ka. Indeed, the ‘failed’ dispersal that Boivin et al. refer to was no dispersal at all. It involved a creature bound to its ecosystem and its niche—albeit a different one—in the same way that it appears the Neanderthals were bound to theirs during their 200-or-so-thousand-year tenure.

Boivin et al. are quite correct in pointing out the equivocal nature of the genomic observations being talked about these past few years. Given the behaviour of the Qafzeh H. sapiens and that of the Neanderthals, a parsimonious reading of the data is that anatomically modern H. sapiens came in contact with, and may indeed have bred with, Neanderthals during the forty or so thousand years that H. sapiens was in the Levant. In all probability there was a frontier somewhere to the north of Qafzeh Cave where the two kinds came in contact for at least some portion of those 40 kyr. Such a scenario makes sense [to me at least] of the genetic evidence that we’re seeing in the present. Any interbreeding that may have gone on between the two species could have been a fait accompli by the time behaviourally/cognitively modern H. sapiens entered Europe. Thus, we dont have to imagine a time when people like us encountered and then mated with Neanderthals.

Further evidence that neither the Qafzeh hominids nor the Neanderthals were like us might be drawn from the observation that there was no extirpation of the Neanderthals coincident with the earlier anatomically modern H. sapiens expansion into the Levant between 100 and 60 kyr ago. In other words, for the 40 or so thousand years during which they were neighbours, there appears to have been no anthropogenic cataclysm comparable to that which many would argue was visited on the Neanderthals during the latest excursion from Africa of cognitively modern H. sapiens like you and me. If, indeed, H. sapiens spelled the doom of the Neanderthals between about 40 and 50 kyr ago, if the Qafzeh hominids were exactly like us, what explains the persistence of the Neanderthals? In the end, Boivin et al.’s narrative ignores the real likelihood that there were evolutionary changes within H. sapiens between the time they occupied Qafzeh Cave at around 100 kyr ago and about 40 kyr ago, when people like us colonized the world.

In the search for answers to the question of when hominids became human, I think the disciplines of archaeology and palaeoanthropology have some distance still to go before gaining a truly accurate accounting of recent evolution.

This piece took me much longer to put together than I had originally anticipated. Next time I’ll have something to say about the latest data on the latest Neanderthals in Spain.

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Can We Talk? ‘My ancestors, myself’ by Jonathan Marks

Before I get started, please rid yourself of the expectation that I’m going after Jonathan Marks about his recent piece on Aeon, ‘My ancestors, myself: Fossil genomics is opening new windows to the past. But the view through them isn’t as clear as we like to think.’ On the contrary. I fully agree with him…right up, that is, to the part where he characterizes the Neanderthals according to the same orthodox archaeological interpretations with which yours truly has a long-standing dispute. Jon can’t be blamed for this. As a consumer of archaeological knowledge, he’s more or less at the mercy of conventional wisdom. So, read on, s’il vous plait.
Illustration by Richard Wilkinson

Can we talk?
     A couple of days ago Jonathan Marks gave us much to ponder about our present understanding of Neanderthals, especially the recent genetic comparisons with modern humans. If I might be allowed to compress it into a sound-bite, Jon’s* is an eloquent essay on the post-modern anthropological insight that, either when one is studying present-day humans, or our recent and fossil relatives, we need always to keep in mind the cultural ‘baggage’ that we bring to our investigations. In particular, he hopes to persuade us that biology, alone, is no measure of a fossil species. I couldn’t agree more. I like to use the following example as a means of illustrating what’s meant by this notion of one’s ‘stance,’ ‘background,’ ‘cultural baggage,’ or however you want to put it. Ask yourself this question: 

What do you think lurks in the cultural and social background of neuroscientists who seek to find structures in the brains of males and females to ‘explain’ perceived differences in the behaviour of the sexes? Is it reasonable to suppose that these invesigators must have ‘bought into’ the idea that, e.g., ‘girls’ can’t do math [but that boys can], or that ‘boys’ are inherently rambunctious [and girls are sugar and spice], or ‘boys’ are promiscuous [but ‘girls’ are chary]? 

I’ll admit that unexamined presuppositions like these might not always be the reason for such scientific enquiries, but it would be an odd coincidence if they weren’t. Jon Marks constructs his argument along these lines, to remind us that our background and experience will enter, more often than not unnoticed, into our deliberations on the ancestry of Homo sapiens, if we don’t at least make an effort to examine our motives and beliefs from the outset.
     Jon makes a great number of very apt observations about the way the Neanderthals are treated in the popular imagination, and in the minds of anthropologists and geneticists. Drawing on recent revelations from genomics–that we share some of the same novel genes with the Neanderthals–he muses on what this might have meant about our relationship with them. Specifically, he asks whether or not the new, modern form of bipedal apes that appeared in Europe around 45 ka would have seen the congeneric Neanderthals as people like them. 
     And it is here that Jon and I diverge. Even though Jon’s applying a set of thoroughly anthropological principles to a perennial question, I’m dismayed because his essay presents as ‘fact’ a picture of the Neanderthals that is, in aggregate, a mélange of what was, what might have been, what never was, and what could never have been. In other words, his ‘take’ on the Neanderthals may be informed by an unknown number of what one day could well turn out to have been archaeological myths. In that, Jon confidently represents the Neanderthals in a way that undermines his own argument.
     He thus applies a culturally constructed ‘skin’ on the anatomical and biological Neanderthal that draws on the orthodoxy of interpretation, without acknowledging that the ‘skin’ comprises what are at best provisional findings as to how they behaved and what they were capable of in comparison to modern humans. [I realize that my own ‘take’ on the Neanderthal archaeological record isn’t mainstream, and most of my peers would dismiss my quarrel with the mainstream as unreasonable. Nevertheless, I have a legitimate dispute with archaeological orthodoxy, and thus my alternative interpretation of record leads me to be cautious, at a minimum, regarding the stories told about the inhabitants of Europe before the time of modern humans.] Jon introduces his Neanderthals in this way

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 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. 

Jon is unequivocal in his conviction that the Neanderthals were ‘cultural’ and ‘humane.’ But how does he make such claims with such certainty?

Shanidar 1 Neanderthal humeri. Individual suffered a crushing
blow to the left temporal, probably leading to blindness and
abnormal development of the right side (shown at left). 
The distal fracture is healed. Researchers conclude that the individual
must have been nursed to have survived such injuries. (Souce: Smithsonian)

Sandhill crane humerus. Individual rescued after months of
flightlessness. X-ray shows a healed, overlapping fracture.
(Source: Wildlife Rehabilitation Center of Minnesota)

In support of this he first mentions healed fractures. These tell him the stricken Neanderthal’s friends and relatives must have taken care of him for a time after the injury. Jon’s referring to the Shanidar 1 remains. This disappoints me, because, quite unreflexively, he is accepting, carte blanche, a thoroughly ethnocentric interpretation of the skeletal evidence–i.e. that to survive such injuries, this individual must have been nursed by relatives and companions. Dettwyler, in the early 90s, pointed out to us that, ethnographically there is a great deal of variability in the way the injured are treated, such that the conventional wisdom about Shanidar 1 is, at best, a sufficient, but not necessary explanation.   
     Besides, there are plenty of examples from the non-human world demonstrating that, even in the absence of palliative care, animals are capable of recovering from injuries that most of us would assume to have been mortal [just as those of Shanidar 1], either immediately, or over time because of reduced mobility and ability to acquire nourishment. You might have thought that a bird with a broken wing would surely perish. Not so. The X-ray at left illustrates a healing fracture of a bird’s humerus. It belongs to a Sandhill crane. They inhabit wetlands, and are stealthy hunters. But their natural history includes plenty of flying about. The X-rayed crane apparently survived for months before the Wildlife Rehabilitation Center of Minnesota rescued it. Presumably it could have survived for many more. So, you see [I might be wagging my finger a bit just now], consumers of archaeological findings must be very careful–those inferences might simply be in error.   
     As for teeth worn from using them as tools, there is broad morphological similarity between the dental attrition visible in Neanderthals and many ethnographic human groups. However, no one, as far as I know, is able, unequivocally, to argue that the two are the result of identical processes.
     I think you can probably guess the eventual outcome of these comments on Jon’s essay. But don’t stop here! Immediately, Jon brings up another very tenuous claim about Neanderthals–that they buried their dead. [But, don’t kid yourself. None of this can be treated as fact,  which you’d know if you’ve been paying attention. However, if you’re coming fresh to this material, I could recommend a one or two articles that might make you think twice about the ‘fact’ of Neanderthal burial. Hell! It made Harold Dibble think twice, and he and his colleagues eventually found good evidence that in the case of an infant Neanderthal long believed to have been purposefully buried, the evidence is, at best, equivocal. And, some would have it, that in those cases, the argument for purposive, mindful behaviour, is *cough* gravely weakened.] I find it odd that he states they built nothing that lasted. Although I have to agree, the absence of such evidence is, you’ll forgive me, not evidence of absence. They could have been building log cabins, for heaven’s sake, which leave no post holes, and which surely would have decomposed over the millenia. Moreover, a number of archaeologists have treated their findings as evidence of structures–the mammoth bones at Moldova, for example, or the imprint of wood in travertine in the Abric Romani rock shelter. I find Jon’s assertion here to be curious, to say the least. So be it.
     Next, he turns to a discussion of how present-day humans [that would be you and me] might have viewed the earliest moderns in Europe, as a way of illustrating his thesis that our cultural baggage gets in the way of a more inclusive ‘take’ on the Neanderthals. He suggests that those modern humans 

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. 

True enough. They may not have been very much like us. But neither are New Guinea highlanders. His point here is that regardless of the specifics of the difference, whether one is talking about Neanderthals or the first moderns in Europe, present-day humans like you and I would have experienced them both as exotic. However, this comparison cannot hold up against the archaeological record, nor that of the ethnographic. In contrast to the traces Neanderthals have left behind [for upwards of 250 kyr], throughout Europe and Asia from about 45 ka modern humans left behind an archaeological record that is readily recognizable to us. That record includes behaviours that in some cases persisted into the twentieth century in many parts of the world [and in remote places continues to this day]. Not so the Neanderthals.
     That same archaeological record shows us that the modern skeletal form of Homo, which emerged briefly from Africa nearly 100 ka, conducted itself in an identical manner to that of their Neanderthal contemporaries–i.e. unlike anything that modern humans have been capable of producing since about 45 ka. Compared to them, we would undoubtedly have recognized as human the first people like us in Europe, and in much the same way we have viewed ethnographic peoples–who’re often very different from westerners. I don’t think the same can be said for the Neanderthals without straining credulity. And so, when Jon writes 

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 [emphasis mine]. 

Quite simply, there’s no unequivocal evidence that either the modern form at 100 kyr ago, or the Neanderthals throughout almost 250 kyr ever ‘thought’ at all. Thinking, you see, may be unique to the modern humans that spread throughout the old world in the blink of an eye around 45 ka. Our experience of the world, beyond the instinctual, is little else but thought. On present understanding, we simply can’t assume that those relations at 100 ka were capable of communicating ‘sensibly’ or behaving ‘properly.’ 
     Jon worries that our view of the Neanderthals is based purely on the physical differences between us. But, as I hope I’ve convinced you, physical differences are not the only yardstick that we use to classify or characterize the similarities and differences between the two. He is correct when he says

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. 

And, if I might add, people that look like you. Once again, we’re being asked to accept the inference that Neanderthals spoke, dressed, and had anything like ‘general interests.’ They may well have not.
     Here is where Jon paints himself into a corner. He’s trying to tell us that the way we see the Neanderthals is coloured by our preceptions, much in the way a bigot is disposed to treat another group as inferior or worse. Yet, he’s asking us to accept that the Neanderthals are human, and for that reason we should be more reflexive and cut them some slack. As he puts it

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. 

As I’ve tried to point out in this blurt, in his acceptance of mainstream inferences about the Neanderthals, Jon is also ‘seeing them in distinctly cultural ways,’ equally unexamined, but different from those he’s arguing against. His view of Neanderthals is every bit as culturally constructed as that of those he seeks to enlighten in this essay. 
     As I said at the outset, I have no quarrel with Jon. I hope it’s clear that I’ve used his essay as a stepping-off point. Sure, I’ve found what I believe to be flaws in ‘My ancestors, myself.’ But those flaws simply convince me that Jon is an unwitting victim of what is a collection of archaeological myths of unknown proportions. 
     Well, I hope you’ve enjoyed this side-trip to the biological anthropological view of the Neanderthals. And I very much thank you for visiting us.

*I sincerely hope that using his given name’s diminutive I’m not being presumptuous. He and I have a facebook acquaintance, but we have corresponded within that. So, here’s hoping. I just don’t feel right referring to him as ‘the author,’ or ‘Marks.’

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