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), http://dx.doi.org/10.1016/j.quaint.2013.01.008)  

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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That Wild and Crazy Casey Luskin Uncorks Another Beauty: Makes Monkeys Out of Professional Palaeoanthropologists

In the beginning was the Word, and the Word was with God, and the Word was God. [1 John 1:1]

I’m beginning to get a sense of the problem. When approaching the voluminous literature of human evolution Young Earthers and Creationists/IDers [i.e. Intelligent Design adherents] can’t get past the habit of believing that [at least some of] what they read as being the revealed word of a deity. As such my colleagues could afford to be a bit more careful when choosing their words. I can easily see why their best efforts feed into the Christian creation myth.
     Notwithstanding his propensity to treat the writings of us as the word of a deity revealed [much like my colleagues come to think of it], Luskin is either very lucky and came up with the foundation for his argument by chance or the man has done his homework and read widely in ‘our’ literature. Such is his virtuosity.
     Shortly before leaving for the Czech Republic in July I felt preternaturally compelled to write about the efforts of Casey Luskin, a lawyer and IDer. At that time he was promising a whole series of tell-all revelations that he reckoned would dissolve the humanist edifice that is our present knowledge of the fossil record. As I now discover, in the interim I’ve missed many more articles by the prolific Mr. Luskin. No worries! The SA news ticker came to the rescue the other day when up popped this: 

THE GENUS HOMO: ALL IN THE FAMILY

Luskin’s major point is a variation of the theme of the earlier article. Australopithecus is an ape; Homo is a human. Read on to find out how he makes monkeys out of my colleagues. 
     I could give Luskin’s whole spiel a pass were it not for the way in which he artfully weaves the words of our colleagues into a narrative that underscores his conclusion–that the appearance of Homo in the fossil record isn’t prefigured by the earlier australopithecines, and is thus strong evidence of the special creation of humanity. Of course, to do so he must paint all members of the genus Homo in such a light that ‘we’ all appear to be like modern humans. And that’s where where my colleagues come in–aiding and abetting Luskin and his ilk with authoritative statements such as the ones included in the medley of the following Luskin quotes [complete with a very scholarly looking list of references cited]. 

‘Donald Johanson suggests that were erectus alive today, it could mate successfully with modern humans to produce fertile offspring.’ [from Lucy]

‘Wood and Collard [reinforce the similarities among members of our genus when they write]: “The numerous associated skeletons of H. neanderthalensis indicate that their body shape was within the range of variation seen in modern humans.” ‘ [That wouldn’t be you, Mark, would it?] [published in Science]

 ‘Erik Trinkaus likewise argues: “They may have had heavier brows or broader noses or stockier builds, but behaviorally, socially and reproductively they were all just people.” ‘ [From an interview in Time]

‘Trinkaus and others say there is no reason to believe they were any less intelligent than the newly arrived ‘modern humans.’ ‘ [Washington Post interview]

‘Fred H. Smith [adds in a Smithsonian interview] “[The first European palaeoanthropologists] believed [Neanderthals] to be scavengers who made primitive tools and were incapable of language or symbolic thought.” Now, … researchers believe that Neanderthals “were highly intelligent, able to adapt to a wide variety of ecological zones, and capable of developing highly functional tools to help them do so. They were quite accomplished.” ‘

‘Francesco d’Errico affirms these comments [in the same Smithsonian article], stating, “Neanderthals were using technology as advanced as that of contemporary anatomically modern humans and were using symbolism in much the same way.” ‘

My dear old friends from the Kebara Cave project add fuel to this fire: ‘ “the morphological basis for human speech capability appears to have been fully developed” in Neanderthals.’

‘Neanderthals made musical instruments like the flute.’ [citing the debunking article in Current Anthropology, as it happens]

‘a report in Nature from 1908 that reports the discovery of a Neanderthal type skeleton wearing chain mail armor.’ [from Notes in Nature, 77 (April 23, 1908): 587, see below.]

[At least Luskin owns up to the preceding two inferences being somewhat ‘uncertain’–would that my colleagues were so circumspect.]

‘Trinkaus says that when comparing ancient Europeans and Neanderthals: “Both groups would seem to us dirty and smelly but, cleaned up, we would understand both to be human. There’s good reason to think that they did as well.” ‘ [Another humdinger from the Washington Post article cited above]

Plunging the knife in even a tad further, Luskin then cites the recent DNA ‘evidence’ that Neanderthals R Us and vice versa. I don’t have to tell you what I and a few others think of those tasty inferences. The author finishes the medley of incriminating statements with: ‘We saw earlier that Leslie Aiello said “Australopithecines are like apes, and the Homo group are like humans.” ‘ [Shame on you Leslie Aiello. You of all people should know that you can’t split the ape family/superfamily into us and them.]

I ask you. How can we expect to gain credibility with the supernaturalists when we so readily feed their doctrinal belief that humans aren’t apes?  At every chance we should be reminding them that humans are nothing if not apes. That oughta get ’em thinking.
     So, let’s all get on the same page and stop these people from making monkeys of us all! 

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