Homo erectus

Chapter 8 of Hoffmeyer's Signs of Meaning in the Universe is about the evolution of language. I really like the opening paragraph, which is worth remembering:

I have observed that many of my students -- who are, of course, studying to become biologists -- are extremely reluctant to accept the idea of human language as something special. They point out that animals such as dogs, whales or chimpanzees might well have a language that we human beings have just been too highfalutin to acknowledge. And, in my experience, my holding up of the novels of Dostoyevsky or the Bible as examples of how human language is something quite unique in this world seems to make no great impact. If anything, I have the feeling that these students look upon humanity, and human nature in general, as a warped work of nature epitomized by its destructive penchant for building concrete blocks of slums and waging war. And, seen in that light, the fact that a few sensitive individuals might find it in themselves to write emotionally harrowing works of fiction does not seem all that strange.

I have to say, I have had the identical experience with students -- down to their arguing that animals may have their own versions of Shakespeare. "Who is to say they don't?" is the argument I have heard a lot.

My reaction is different than Hoffmeyer's, though. For one thing, these students have a long upbringing of being told it is wrong to make value judgments; for another, they have a long upbringing of watching movies with talking animal characters who emote with real human feeling.

I surmise it is difficult for some to imagine how any animal could exist without human-like mental capabilities.

As a corollary, I often ask my classes whether they would rather be hunted by a human or by a chimpanzee. I have never yet had a class where more than a few students choose the chimpanzee -- even though a chimpanzee would be enormously less dangerous as an enemy than a human. (For one thing, a chimpanzee is rather less likely to continue to track you after dark...) It seems to come down to a fear of the unfamiliar, and the optimistic idea that you could reason with a human enemy.

I choose not to worry until the army breeds a legion of warrior chimps.

In any event, Hoffmeyer cites Merlin Donald (1991) for much of his scenario for language evolution. The basic idea was that there was an intermediate stage between apelike minds and human language that was based on mimetic abilities, "the ability to carry out collective motor-based reconstructions of earlier incidents." Mimetic culture required and built upon social intelligence (and associated social learning abilities), but it also required a link between episodic memory (remembering events) and procedural memory (remembering how to carry out an action). Ultimately, these led to an internal syntactic memory that helped organize conscious thought, a system from which language sprung.

Under this scenario, mimetic culture characterized Homo erectus, who lacked language, but shared most other mental characteristics with humans.

This passage raises an interesting idea:

It is a fascinating thought that Homo erectus, with a brain capacity not really so far removed from the present dimensions or our own brains, may have been very much like us in almost all respects -- and, especially from an emotional point of view, in the most profound ways. Why, were it not for that one little quirk -- the lexicon, that ability to send our inner experiences flowing from our lips in streams of words to be pondered and debated among ourselves, adopted or rejected -- we might be said to have been almost identical at birth. The difference between the talking Homo sapiens and Homo erectus may not have been any greater than that between the people of the later Stone Age and the people of today. Because what separates modern man from Stone Age man is the existence of external (extrasomatic) memory banks -- first and foremost the written word in the form of books, but also the legacy of sculptures, pictures, buildings, tools and, these days, computers. The presence of these external memory banks implies that we, as adults, bear the burden not only of our own inherent intellectual legacy but also of a hundred-generation-long struggle to extract the essence of our forefathers' experience. This struggle has taught us to live in a world saturated by science, technology and art -- a world which could quite conceivably create an even greater gap between us and the mind of Stone Age man than Stone Age man, by virtue of the spoken word, created between himself and the mind of Homo erectus.

Now, this seems vital to me: is the extent of human variation today -- a result of recent genetic and cultural differentiation -- as great as the difference between Homo erectus and modern humans? Hoffmeyer considers the problem in terms of culture alone, and concludes that the difference might well be as great.

In support of this, he suggests that the early effects of culture on brain development generate possibly vast phenotypic differences among humans:

[Differences in programmed cell death] results in the cultural stamp leaving a telling imprint on the neurological structure of the brain. If not at birth then certainly by the time they start school modern human beings are therefore already very different from the people of the Stone Age. Just to be on the safe side it ought also to be mentioned that this restructuring of the neurological terrain is not altogether irrevocable. It appears at any rate that, even in adults, the area of the cerebral cortex which registers hand movements can be expanded or reduced as required. But for anyone desirous of reverting to the Stone Age mentality it would hardly be enough just to journey back to the settlement at Vendsyssel-Thy. You would have to retreat pretty far into the Siberian taiga and stay there for years, and in fact it would be best to start out in early childhood.

Of course, there are modern humans living in such contexts today. What about them? The "Stone Age - modern" difference is not merely a temporal comparison (prehistoric vs. today), it is also a geographic and cultural comparison (civilization vs. hunter-gatherer). From this perspective, Hoffmeyer's point easily misfires -- the claim would seem to require that the integration of a Homo erectus-like human into a modern hunter-gatherer group should be no more difficult than the integration of today's hunter-gatherers into civilization.

But modern hunter-gatherers do have many problems integrating into larger societies. The ability to speak is not particularly a barrier, but linguistic differences are. Culture, technology, and economics are all barriers. Probably the most severe barrier is disease.

Archaeologists have a long history of using modern hunter-gatherers as analogues for ancient humans precisely because of their differences from larger societies in terms of economy, subsistence, and social organization. That analogy assumes that the gulf between Homo erectus or other ancient hominids and modern hunter-gatherers is not so great. This tradition has emphasized certain effects of language and symbolic culture, such as an increase in the possible size of social units, breadth of economic and trade relationships, and sophistication of technology.

Modern and historic hunter-gatherers are diverse in these aspects of behavior -- everything from marriage patterns, kinship ties, and food acquisition strategies to land tenure and dispersal strategies. Certainly such diversity itself would be impossible in the absence of language: could different kinship systems be possible in the absence of the linguistic structures that support them? Or different taboos?

Two perspectives present themselves. One point of view would see the variation among modern humans as highly significant; a clear indicator of symbolic culture and language and a strong element in shaping diversity in the minds of modern humans. The other point of view would see the minds of modern humans as essentially similar despite any cultural differences, in which case symbolic culture and language can have had little effect on minds outside the relatively narrow parts driving symbolic culture and language.

The two perspectives are very different in their predictions about differences among modern human minds. But they are essentially the same with regard to the archaic-modern human differences compared to modern human variation.

References:

Donald M. 1991. Origin of the Modern Mind: Three Stages in the Evolution of Culture and Cognition. Harvard University Press, Cambridge MA. Amazon

Hoffmeyer J. 1996. Signs of Meaning in the Universe. Indiana University Press, Bloomington IN. Amazon

The current Science has meetings reports from the Indo-Pacific Prehistory Association Congress, including this article by Richard Stone about excavations from Sangiran:

At the meeting, archaeologist Harry Widianto of the National Research Centre of Archaeology in Yogyakarta, Indonesia, wowed colleagues with slides showing stone tools found in sediments that he says were laid down 1.2 million years ago and could be as old as 1.6 million years. The find, at a famous hominid site called Sangiran in the Solo Basin of Central Java, "opens up a whole new window into the lifeways of Java Man," says paleoanthropologist Russell L. Ciochon of the University of Iowa in Iowa City.

This report is the latest in a series of finds from the site, which have been increasing in date:

Over 2 months, they unearthed 220 flakes--several centimeters long, primarily made of chalcedony, and ranging in color from beige to blood red--in a 3-by-3-meter section of sand deposited by an ancient river.

The find, not yet published, could be even more spectacular than Widianto realizes, says Ciochon. His team, which also works at Sangiran, has used ultraprecise argon-argon radiometric methods to date the volcanic strata overlying the levels excavated by Widianto to 1.58 million to 1.51 million years ago--making the flakes at least 1.6 million years old. If the flakes were undisturbed, Ciochon says, they would represent "some of the earliest evidence of the human manufacture of stone artifacts outside of Africa." Their antiquity would match that of the oldest flakes found in China, at Majuangou, dated to 1.66 million years ago and also made of chert.

The article includes a picture of some of the tools, which are small flakes on a fine-textured material.

The Sangiran flakes "are fundamentally different"--smaller--than the stone choppers made by H. erectus in Africa, says Ciochon. The evidence, he argues, suggests that Java Man had to range far for small deposits of good flint or chert and so created small, finely worked tools in contrast to the larger tools found in Africa.

There certainly is a contrast in the absence of large core tools, but it would take a close study to show that the flakes are different. But if there was a conscious limit to the selection of good raw materials, that might be significant also.

There is no hard endpoint to the Acheulean; its tool types -- in particular the handaxe -- last well into the MSA/Middle Paleolithic. Here are some notes on the later occurrences in Africa:

Sheppard and Kleindienst (1996) considered the technological changes from ESA to MSA at Kalambo Falls, finding:

...there is little change, at this site, in the basic techniques of blank production or the attributes of the blanks produced from the ESA to the MSA. The only marked change to occur is the loss of large cutting tools (hand axes, cleavers) and their replacement by heavy-duty forms (core axes, picks). It is hypothesized that this change marks a decline in portability as a factor in the design of large edge tools (Sheppard and Kleindienst 1996:171).

McBrearty (2003) reflects on the late persistence of characteristic Acheulean handaxes in association with some of the earliest fossils of "modern" humans, the Herto hominids from the Middle Awash of Ethiopia:

At 160-154 ka, the Herto handaxes are the latest survivors of Acheulean technology known in Africa. Formerly, the best candidates were those from the site of Rooidam, South Africa, where a U-series date indicated they might date to ~ 170 ka (Szabo and Butzer 1979). K/Ar dates of ~ 240 ka for Acheulean artifacts from the Kapthurin Formation, Kenya (Leakey et al. 1969, Tallon 1978) have frequently been cited as the date for terminal Acheulean in east Africa, but new more precise 40Ar/39Ar dating now shows these to predate 285 ka (Deino and McBrearty 2002).

What does the presence of Acheulean tools at 160 ka signify? The nature of archaeological change in the African Middle Pleistocene is murky, but the most obvious development is the abandonment of Acheulean technology, usually thought to have been made by H. erectus and its replacement by implements of MSA traditions, believed to have been produced by H. sapiens. In a nutshell, this comprises the replacement of handaxes and cleavers by points, signifying a shift from hand-held to hafted tools, and the birth of projectile technology. The presence of Levallois technology is usually considered to be a feature of the MSA, but it is present in late Acheulean contexts as well. In fact, the big flakes used to make African late Acheulean handaxes, including some Herto and Kapthurin specimens, may be struck from Levallois cores....The earliest MSA points were once thought to be those from Gademotta, Ethiopia, dated by K/Ar to 235 ka (Wendorf et al. 1994). Retouched points from the Kapthurin Formation predate those from Gademotta by 50,000 years. Dated by 40/Ar/39Ar to > 285 ka (Deino and McBrearty 2002), the are currently the oldest in Africa. A similar date is estimated for the basal MSA at Florisbad, South Africa (Grün et al. 1996), though these levels have not yet yielded points (Kuman and Clarke 1986, Kuman et al. 1999). Both retouched points and Levallois points have been recovered at Twin Rivers, Zambia, where they are dated by U-series to 265 ka (Barham 2000) (McBrearty 2003:1-2).

McBrearty briefly discusses two alterative hypotheses. One is that the Acheulean handaxes are markers of a biological species, and that MSA points and other artifacts were made by some other species, or multiple species. The problems with this hypothesis are manifold, including the association of the handaxes with fossil remains that would be uncomfortable fits in H. erectus at best. Yet, the hypothesis can be sustained by the additional assumption that multiple species cooccupied the same African paleolandscapes with sufficient contemporaneity to drop their tools in the same places:

Or can the archaeological record of the African Middle Pleistocene represent the behaviour of several species? Might different tools be the distinctive signatures of different populations or species who are competing with each other for the same territory and resources? A similar scenario of interspecific competition seems to have been played out between H. sapiens and the Neanderthals in Europe after 40 ka, but there the replacement was complete within 10,000 years or so. Africa is a far more enormous continent than Europe, its Pleistocene population far less dense, and our knowledge of its record less finely resolved. The 125,000 years represented by the Acheulean to Middle Stone Age transition in Africa is more than four times greater than the entire timespan of the residence of H. sapiens in Europe, but only a handful of African sites from this long time period have yet been explored.

The other hypothesis is that the handaxe appears wherever it is functionally relevant, regardless of phylogeny. Acheulean elements may have been independently invented again and again:

Archaeologists routinely stress the uniformity of the Acheulean tradition, and rarely entertain the possibility that the category 'handaxe' is an artificial construct that we impose upon the material. Experimental work by Jones (1994) shows that the familiar tear-drop shape of the handaxe is a design compromise resulting from attempts to gain the maximum cutting edge from the minimum weight of stone. The same techniques of blank production and bifacial retouch were employed in many cases to make both Acheulean handaxes and MSA points, and in the Kapthurin Formation the two classes of artefacts can grade into each other. Furthermore the tear drop shape occurs repeatedly in the archaeological record in cases where there is no evidence of 'phylogenetic' relation. Many projectile points from Africa, Europe, the Near East, and even the New World have similar plan forms (McBrearty 2001; Otte 2003), but there is clearly no 'phylogenetic' relationship among them. Rather, the recurrence of this target form demonstrates the design constraints inherent in fractured stone, and it appears to have been rediscovered repeatedly by tool makers in the course of prehistory (McBrearty 2003:2-3).

Of course, if the recurrence of the handaxe across the 1.4 million years of the Acheulean resulted from its function rather than a continuous chain cultural transmission, then it takes away one of the principal pieces of evidence that Acheulean people had any substantive culture at all.

As far as handaxes are concerned, that may be a good thing. The maintenance of a single cultural tradition across much of three continents over a million years by exclusively social transmission seems incredible. Some have suggested that the handaxe is hardwired into the human genome, a proposition that seems even less credible (at least, to me). Absent these means of transmission, we are left with the proposition that the handaxe did not fade from the earth because of its functional utility -- either it was the tool that did the job the best, or it was the best tool that humans were capable of making that did the job adequately. If function and human ability combined to make it so persistent, it should not be the least bit surprising that the form should recur in later contexts -- in the scenario of recurrent invention, it never really went away. The production of handaxes on large Levallois flakes seems especially relevant.

One view of the uniformity of handaxe variation across space is that humans maintained strong cultural links across large distances. The knowledge of handaxe production and the concept of handaxe shape were highly conserved cultural markers that were widely spread.

But the alternative hypothesis, that handaxe form was repeatedly invented by hominids and actually served as the best possible tool given its purpose and hominid flaking capacities, does not require long-distance cultural interactions to maintain the uniformity of the tradition. Nor does it require the recurrent movement of people over vast distances to spread the information. Given the lack of evidence for such long-distance movement, this hypothesis gains a bit of credibility.

Raw material utilization in the Acheulean is highly localized. People may have been using the large tools as repositories for further flaking, and they may have curated them for some time. But they did not transport them over vast distances. Ordinarily, Acheulean people do not appear to have transported material over distances greater than the possible daily movement of a single individual -- a few tens of kilometers.

It raises an obvious question: Is high mobility (in other words, hunter-gatherer-like mobility) a shibboleth of the assumption that handaxe form required culture? Did earlier humans actually have very small, limited home ranges and daily movement patterns? After all, if humans carried handaxes around for their utility, and they didn't manufacture a new one every day, then some handaxes ought to represent week-long movements or even longer.

References:

Sheppard PJ, Kleindienst MR. 1996. Technological change in the Earlier and Middle Stone Age of Kalambo Falls (Zambia). Afr Archaeol Rev 13:171-196. DOI link

McBrearty S. 2003. Patterns of technological change at the origin of Homo sapiens. Before Farming 3:1-6.

In Nature a couple of weeks ago, Robin Dennell and Wil Roebroeks had a provocative paper exploring the possibility that early humans (i.e. Homo erectus) originated in Asia rather than Africa.

The paper is all speculation of course; there is no evidence of any earlier hominid in Asia.

But it is the good kind of speculation. Although maybe not quite this big:

Most probably, we are on the threshold of a profound transformation of our understanding of early hominin evolution that might prove as far-reaching as the demise of the notion of Man the Hunter in the early 1960s (Dennell and Roebroeks 2005:1103).

Here's the abstract:

The past decade has seen the Pliocene and Pleistocene fossil hominin record enriched by the addition of at least ten new taxa, including the Early Pleistocene, small-brained hominins from Dmanisi, Georgia, and the diminutive Late Pleistocene Homo floresiensis from Flores, Indonesia. At the same time, Asia's earliest hominin presence has been extended up to 1.8 Myr ago, hundreds of thousands of years earlier than previously envisaged. Nevertheless, the preferred explanation for the first appearance of hominins outside Africa has remained virtually unchanged. We show here that it is time to develop alternatives to one of palaeoanthropology's most basic paradigms: 'Out of Africa 1' (Dennell and Roebroeks 2005:1099).

It is worth reviewing exactly what "Out of Africa 1" is supposed to be. The paradigm is that emergence of hominids from Africa required increases in brain size and/or body size, coincident with the emergence of hominids like KNM-ER 3733, KNM-WT 15000, and others. The motivation for this hypothesis is simple: australopithecines have not been found outside of Africa. Nor has anything like Homo habilis, which is australopithecine-sized but has larger brains.

Of course, it is questionable just how basic this paradigm is. Consider what I (and my colleagues) were able to write only seven years ago:

The problem is that significant range expansion out of Africa occurred a half million years or more later than the first H. sapiens [corresponding to others' H. erectus or H. ergaster]. Population size before then may have remained small, and this is not an inconsequential time span, being one quarter of the time H. sapiens has existed. An important date in behavioral evolution is 1.5 MYA because it is marked by the earliest appearance of the Acheulean, the ubiquitous hand-axe industry of the Early and Middle Pleistocene.... Before this time, humanity was limited to Africa and immediately adjacent sections of Asia such as the Levant (Hawks et al. 2000:7).

Evidence for large body size in Late Pliocene humans (notably KNM-WT 15000 but also many others) made it very plausible that larger bodies were necessary for dispersal from Africa. But without good evidence for such dispersal before around 1.4 million years ago (and arguably not before 1 million years), larger bodies could not be assumed to be a sufficient condition for dispersal. Writing about the origin of humans, we had to consider all these alternatives -- at a time when the Dmanisi sample consisted of a single uncertainly dated mandible and the Mojokerto date stood alone with very questionable provenience.

Now we know that hominids did leave Africa by at least 1.8 million years ago. Dmanisi has almost singlehandedly changed the perspective.

And in doing so, it made much more convenient the hypothesis that large body size was both necessary and sufficient for dispersal from Africa. If the date of dispersal and the date of human origins are the same, then it is natural to propose that the coincidence is more than chance.

I would say this is more of a convenient hypothesis (and an easy story to tell) than it is a basic paradigm. The idea that large body size caused dispersal from Africa may have been a local minimum in terms of parsimony (at least as long as the body size of the Dmanisi fossils was not known), but it was only one alternative among many still in play.

And it remains a plausible hypothesis -- after all, the Dmanisi remains are a bit larger than australopithecines, and they might well have shrunk from a larger early-human-like size after reaching Asia instead of before.

But Dennell and Roebroeks give motivations for examining some alternatives.

The only reason why the earliest tool assemblages in Asia are attributed to H. erectus s.l. is that palaeoanthropologists have already decided that, in effect, it was the only hominin capable of migration out of Africa, and with sufficient Wanderlust to do so (Dennella and Roebroeks 2005:1099).

Homo erectus sensu lato (s.l.) means Homo erectus "in the loose sense", which would include not only the "strict sense" (sensu stricto) H. erectus. from Java and China, but also hominids like OH 9 and KNM-ER 3733 from Africa, and presumably the Dmanisi hominids.

A long passage reviews the total faunal evidence from Asia during the Late Pliocene. The thrust of the passage is that there are very few sites with extensive fauna, and of these most preserve mainly large-bodied herbivores. There are a few hints that a hominid-friendly fauna may have existed, including the presence of baboons. But there are no hominids of any kind at the vast majority of Asian localities -- Dmanisi is a real exception in the Plio-Pleistocene record.

This is the key taphonomic argument: if we have only found Early Pleistocene humans from continental Asia within the past ten years, then how can we preclude there having been australopithecines there? Dennell and Roebroeks argue that if there were australopithecines, we shouldn't necessarily expect to have found them yet -- we just haven't looked extensively enough.

A close read of the section raises a caution, though. One of the main arguments for the incompleteness of the Asian record is that sites don't preserve each others' fauna.

It is also likely that the full range of taxa is incomplete for the Indian subcontinent, because Megantereon and Pachycrocuta are not recorded in India but are present in Pakistan; in Pakistan, there is no evidence of Camelus and small primates, and in neither country is Homotherium recorded, although this is present to the west at Dmanisi, to the north at Kuruksay, central Asia and to the east at Longuppo, south China (Dennell and Roebroeks 2005:1100).

Of course, all of these species are recorded in Asia taking all the sites in aggregate; this is hardly an argument for the overall weakness of the record -- just an argument that no individual site is an adequate record of the continent's fauna.

To me, the important question is not whether australopithecines as currently known from Africa were in Asia. A more troubling possibility is that the australopithecines that we now know from Africa were not the only (or main) manifestations of early hominids in Africa. Large parts of Africa that we might expect to be congenial to hominids, like the Zambesi basin, have few or no fossils at all. The recovery of the Bahr el Ghazal mandible (Brunet et al. 1994) certainly makes clear that hominids were living across a much larger area than we have adequately sampled. But that mandible is, although not identical, certainly very similar to known contemporary hominids in its adaptation.

The question is whether hominids had adapted to other ecologies that are much less satisfactorily sampled than the East African rift. They probably weren't living where chimpanzee and gorilla ancestors did, but where else might they have been? Some such ecologies -- like the coasts -- would make early dispersal very plausible.

(In this regard, early humans are not the only hominids who lack a satisfactory ancestor. Who was the ancestor of A. aethiopicus? In what ecology did the first robust hominid arise?)

So what is the broader set of hypotheses that we should consider? Dennell and Roebroeks suggest:

If the above taphonomic review suggests that we cannot show the absence of hominins from areas in Asia at a time before the little evidence we have indicates their presence, we need to consider alternatives to the current Out of Africa [that is, their "Out of Africa 1"] model. There are three issues here. The first is when hominin(s) first left Africa -- might they, for example, have left shortly after they acquired the ability to make stone tools, the earliest of which are currently 2.6 Myr old? Or could they have left even earlier, about 3.0Ð3.5 Myr ago, when some australopithecines were already living in the African grasslands? The second issue is whether we yet know the full range of hominins that inhabited both Africa and Asia in the Late Pliocene and Early Pleistocene. Even in east Africa, several new taxa have been claimed in the past decade (for example, A. anamensis, A. garhi, Ardipithecus ramidus and Kenyanthropus platyops) and doubtless more will be found. (An indication of how little we know about Pleistocene east Africa is that only recently has the first fossil evidence for chimpanzee been found.) In Asia, the recent discoveries of H. georgicus and H. floresiensis should make us very wary of assuming that H. erectus s.l. was the only player on the Asian stage in the Early Pleistocene. Third, Asia might not have been the passive recipient of whatever migrated out of Africa but might have been a major donor to speciation events, as well as dispersals back into Africa. Such two-way traffic is well documented for other mammals in the Pliocene and Early Pleistocene, such as Equus and bovids, with more taxa migrating into than out of Africa. There is no reason why hominin migrations were always from Africa into Asia, and movements in the opposite direction might also have occurred, as has been suggested for the Olduvai OH9 (refs 13, 58) and Daka specimens. We should even allow for the possibility that H. ergaster originated in Asia and perhaps explain its lack of an obvious east African ancestry as the result of immigration rather than a short (and undocumented) process of anagenetic (in situ) evolution (Dennell and Roebroeks 2005:1100-1101).

Of course, most of the evidence indicating the presence of hominids is not fossil but archaeological. On this topic, Dennell and Roebroeks have much to say:

Any stone tool assemblage in Asia dated as older than 1.9 Myr ago (the earliest date that Homo is supposed to have left Africa) is either dismissed or (more usually) ignored; undated Oldowan tools are assumed to date from after 1.9 Myr ago and not from 2.6 Myr ago (the date of their first appearance in east Africa); and stone tool assemblages in Asia dated to the Olduvai Event (1.77Ð1.95 Myr ago) and not associated with hominin remains are automatically attributed to Homo erectus s.l. However, there is no reason why Oldowan assemblages in Arabia cannot be older than 1.9 Myr old, or why the tools from Ain Hanech (Algeria) or Erq el Ahmar (Israel) were made by H. erectus s.l. [instead of other hominids] (ibid:1102, references omitted).

There is a section about what exactly absence of evidence can tell, a short critique of using continents as proxies for biogeographic units:

As noted earlier, Pliocene grasslands extended all the way from west Africa to north China, and 'Savannahstan' might prove a more useful spatial unit for modelling early hominin adaptations and dispersals within them than simply an undifferentiated 'Africa' or 'Asia'. For example, the African hominins 1.9Ð1.7 Myr ago at Koobi Fora (Kenya) and Ain Hanech (Algeria), and their slightly later counterparts in Asia at 'Ubeidiya (Israel), and Majuangou (north China) were all living in broadly comparable grassland environments, and it makes sense to place them within the same frame of reference.

I think there is much of value to consider here; but it is less a revolution and more a statement of the field in transition. There are also alternatives that are not considered in this paper but that may be equally plausible -- most notably, the idea that early humans themselves may have been substantially polymorphic (witness KNM-ER 42700), or that brain size rather than body size may have been a prerequisite to dispersal (since habilines, Dmanisi, and H. erectus s.l. are all allometrically similar in brain size).

National Geographic News also has an article about the paper.

References:

Dennell R, Roebroeks W. 2005. An Asian perspective on early human dispersal from Africa. Nature 438:1099-1104. Full text (subscription)

Hawks J, Hunley K, Lee S-H, Wolpoff M. 2000. Population bottlenecks and Pleistocene human evolution. Mol Biol Evol 17:2-22.