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.

SA announces new posts on the Subversive Archaeologist‘s facebook page (mirrored on Rob Gargett’s news feed), on Robert H. Gargett‘s page, Rob Gargett‘s twitter account, and his Google+ page. A few of you have already signed up to receive email when I post. Others have subscribed to the blog’s RSS feeds. You can also become a ‘member’ of the blog through Google Friend Connect. Thank you for your continued patronage. You’re the reason I do this.

A Black Spot on Palaeolithic Archaeology: The Two Bitumen-Splattered Mousterian Artifacts from Umm el Tlal, Syria.

I very much hope that my absence from your ‘puter or mobile from time to time means that my unconscious is cooking something up of which I’m not aware until it pops into my head. O’ course, I’ve pretty much covered everything at least once by now. Maybe I should hang up my spurs. Seriously. Who wants to hear the same blah, blah, blah every time they pop their head in? Let me see… *scratches head* Oh! Thanks, unconscious! Here’s something.
     Somehow or other this baby snuck past me back in ’96. Hmmm. 8-month-old baby. Fieldwork. More fieldwork. Job hunt. Baby. I’m gonna cut myself a little slack for missing it. Besides, I’ve said plenty about similar somethings in the past. Surely I’ve covered this. *searches the SA for keyword Umm el Tlel* Nothing. Hmmm. Guess I have some work to do. *rubs hands together with obvious glee*
     OK. Straight face. Published in Nature 380, 336–338, “Bitumen as hafting material on Middle Palaeolithic artifacts,” by Eric Boëda et al. [I should mention that I’m acquainted with two of the co-authors—Hélène Valladas and Norbert Mercier. We met while I was working at Kebara Cave in 1989. Everyone treated me well that summer. But Hélène and Norbert were extra kind. I even shared a room with Norbert for a week or so while we were staying at a hotel at Zikhron Ya’aqov toward the end of the season. Which reminds me. Contemporary PhD students Michael Spiers, Steve Churchill, Dan Lieberman, Ann Délange, and Erella Hovers were also there that summer. Small world. Sort of.]
     Anyway. Bitumen. Hafting. I’ve previously handled several insupportable claims for Middle Palaeolithic hafting—here, here, here and here, to name but a few… One more won’t hurt.

From Boëda et al., 1996.

    According to the map Umm el Tlal is near the present-day village of El Kowm. It looks to be about 50 km from Bichri Djebel, in what’s now Syria. In the uppermost Mousterian level the team found two lithic artifacts that are stained with bitumen. I have no argument with the chemists on this one. I’m willing to give them that much. These two [count ’em. Two!] bits of rock—one a convergent side-scraper [in the old Bordesian typology; one a 4-cm quadrangular flake—bear traces of bitumen in places where the authors want us to believe that bitumen would preserve if they’d been hafted to sticks. Have a look below. The solid black portions depicted in a are representations of traces of bitumen. As are the similarly solid black portions of the little flake shown in c, further down[I have to say that the black bits on the smaller flake are kind of lost in amongst the very dark lines indicating the Hertzian ripples. Thus, it’s difficult, really, to know what’s bitumen and what isn’t were c is concerned.]
     I find it fascinating that, on the evidence, Nature even bothered to send this paper to referees. And the referees ought to be put in the stocks.

From Boëda et al., 1996.

With regard to the convergent side-scraper the bitumen remnant is interpreted thusly:

The trace of bitumen is present on both faces of the side-scraper and, except at the point, it follows the curve of the right side of the tool, 1 cm below its edge. The left side and the proximal end of the tool were set into a handle. 

So, lemme get this straight. We have an intermittent streak of bitumen on the dorsal surface. No bitumen present on the proximal surface. No bitumen visible on the entire left side of the artifact. Yet, we’re expected to believe the interpretation given in b, that almost the entire surface was buried in the haft. I think we must presume that the bitumen on the side not shown is less suggestive than what we can see in this diagram. Otherwise, why leave it a mystery. Regardless, I think it’s a real stretch [based on the illustration, mind you] to infer, first of all, that the bitumen had once coated a substantially greater area. It’s also difficult for me to accept that the mere presence of bitumen can be taken as prima facie evidence that this artifact was hafted.
     Consider the distribution of the bitumen. I don’t know much, if anything, about bitumen taphonomy, but if some bitumen is still adhering to this artifact, where did the rest go? Sure, the two linear patches near the distal end roughly parallel the retouched right margin. And it’s true, the distal-most 0.5 cm of the longer patch appears to roughtly parallel the same margin. But the remainder of the larger ‘stain’ wanders away from the right margin, up to, but not across the medial ridge of a flake scar on the left half, and then turns abruptly back toward the right margin, but extends to the right margin—not stopping 1 cm from it, which is how the atuhors interpret the distal-most 1.5 cm of the bitumen stain. How are we supposed to know, from the distribution, that the stick wasn’t hafted along the right margin and proximal end?
     If the bitumen had originally coated the lefterly portion of the flake such that it cemented a haft to the majority of the artifact, why has it remained in certain places, but not others? And are we to believe that the tool-maker fashioned a haft to fit the side-scraper, then only smeared bitumen along the haft-flake boundary? I couldn’t imagine that. Could you? Moreover, it seems to me that, if the authors can completely ignore the absence of bitumen elsewhere on the artifact, implying to me that there has been a random loss of bitumen over the ages, I’m feel that I’m well within my rights to suggest that the bitumen was never there in the first place!
     As for the conclusion that the presence of bitumen can be straightforwardly inferred to mean that it was being used as hafting cement, I have to say that I find it implausible. I can say that unflinchingly, if only because the little 4-cm flakoid shown below would prob’ly be the last bit of rock that a sentient being would want to haft to make a handled tool. Were there no Levallois flakes to be hafted? There were some Levallois remains at Umm el Tlal. But, no Levallois points, either? No Levallois blades? Surely those late Neanderthals weren’t so desperate to use this tiny, nearly useless piece of rock that they hafted it so they could get a grip! [So is the idea that anyone would haft over a perfectly good edge (i.e. the left margin of the convergent scraper). Likewise, who’d haft a side scraper lengthwise? Wouldn’t it make more sense to haft it perpendicular to the long axis?]
     I think it’s the authors who should get a grip! It’s, it’s, scandalous to think that they could have gotten away with this! I’m completely flummoxed. Hey, maybe that’s why Nature published it. Maybe they got confused, and were so embarrassed that the editor and the referees all let it pass. Yeah. That’s it. That’s the ticket!

From Boëda et al., 1996.

Geez, Dr. Science, how did the bitumen get there in the first place, if it wasn’t put there by a Neanderthal? Hmmm. Let’s see. I can think of half a dozen possibilities, none of which depend on a source of bitumen close to the Umm el Tlal. The authors point out that Bichri Djebel is the nearest known source of naturally occurring bitumen. However, the chemical signature of the Umm el Tlal bitumen isn’t chemically identical with that of the nearby Bichri Djebel site, nor of the Hit site downstream. Not that it matters to me that we don’t know the source of the bitumen. What difference could it possibly make?
     The authors finish with the finding that the bitumen was heated to a high temperature before its putative use as a hafting cement. Hmm. Naturally occurring bitumen, meet naturally occurring fire.  
     Unknown source. Unknown process by which bitumen came to be adhering to two small lumps of rock. Not much to hang an argument on [I wouldn’t have thought].

     It should be fairly clear that this article, which claims to present evidence of an activity previously unknown among the Neanderthals, might just as well have claimed those same Ns were building rockets to the moon. There’s just about an equal amount of support for that conclusion in the evidence from Umm el Tlal.

My Gawd. Will it never stop???

SA announces new posts on the Subversive Archaeologist‘s facebook page (mirrored on Rob Gargett’s news feed), on Robert H. Gargett‘s page, Rob Gargett‘s twitter account, and his Google+ page. A few of you have already signed up to receive email when I post. Others have subscribed to the blog’s RSS feeds. You can also become a ‘member’ of the blog through Google Friend Connect. Thank you for your continued patronage. You’re the reason I do this.