Koobi Fora

The coming attractions bin at Journal of Human Evolution includes a paper by Kaye Reed, reviewing the evidence of paleoenvironment in the Hadar formation:

Habitat reconstructions of 12 submembers of the Hadar and Busidima formations (˜3.8-2.35 Ma) are presented here along with faunal differences in these submembers through time. Habitats with medium density tree and bush cover dominated the landscape through much of the earlier time period in the Hadar Formation. The lowermost Sidi Hakoma Member is the most closed habitat. The Denen Dora Member shows the influence of frequent floodplain edaphic grasslands with high abundances of reducin bovids. There is an influx of ungulates in the Kada Hadar Member (˜3.2-˜2.96 Ma) that indicates a more arid habitat populated by mammals that were recovered from earlier deposits further south in Ethiopia and Kenya. In the younger deposits from the Busidima Formation at Hadar, the landscape was open wooded grassland with some floodplain environments. The fossil assemblages from the Busidima Formation show a substantial species turnover. Although high numbers of A. afarensis specimens are associated with the lower Sidi Hakoma Member, they clearly inhabited a variety of habitats throughout the entire Hadar Formation. Australopithecus afarensis from Laetoli through Hadar times appears to have been a eurytopic species.

This is a nicely detailed paper, focusing on the amount of wooded/bush habitat, the relation of the hominids to those habitats, and the relative lack of early faunal exchanges with areas further to the south.

The discussion focuses on the range of paleoecologies in which fossil A. afarensis has been found -- including not only Hadar but also nearby Maka and Dikika, and more distant Koobi Fora and Laetoli. Altogether, these localities cover a long time (from before 3.5 up to around 2.9 million years ago). From the range of paleoecologies reconstructed in this paper at Hadar, Reed concludes that A. afarensis did not have a "narrow" habitat preference. It is found in relatively closed woodland, open woodland/bush, and wet grassland/marshland.

There are some differences between localities. At Koobi Fora, relatively few specimens of A. afarensis have been found in the Tulu Bor Member, despite the fact that it occupies the same time as the Hadar sequence. Based on the paleoecological data, Reed suggests that Hadar was a wetter, more closed woodland habitat than Koobi Fora at that time -- Koobi Fora would have included more scrubland punctuated with wetlands and floodplains (here she cites her own 1997 paper).

The early end of the A. afarensis sample is represented at Laetoli. Reed gives a brief review of the paleoecology of that site, which has been interpreted differently by different authors but broadly appears to have had a fairly high amount of rainfall and some patches of forest amid closed woodland:

Thus, the earliest known A. afarensis material was found in deposits showing habitats in which trees and or bushes were fairly plentiful. It is also interesting to note that while the deposits of A. afarensis at Laetoli and Hadar share some perissodactyls, giraffids, suids, and proboscideans, the bovid taxa and those primates other than A. afarensis are not very similar.

Reed concludes that A. afarensis was a "eurytopic" species -- one that inhabited a wide range of habitats and moved broadly across space. It contrasts with the more habitat-selective ("stenotopic") species, which include most of the bovids.

White et al. (1993) suggested broad habitat tolerance for A. afarensis, and indeed, the species has thus far been recovered from regions in which the reconstructed habitat ranges from closed woodland through more open, but wet woodland and shrubland. There is no direct evidence that A. afarensis only existed in riverine forests or grassland habitats, or that they preferred one habitat over another. It is tempting to equate the aridification in the Kada Hadar Member with the extinction of A. afarensis. However, sediments at Hadar are sparse or missing altogether from ˜2.90-2.35 Ma thus obscuring details of the species' demise. All that can be said is that they are no longer present at 2.35 Ma and most of the fauna, including hominins, has been replaced.

References:

Reed KE. 2008. Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.08.013

Just noticing, in this John Noble Wilford article:

A new report, to be published Thursday in Nature, will review more skeletal evidence of the transitional aspects of the Dmanisi specimens.

More later...

UPDATE(2007/09/18): Wilford doesn't directly state the article's theme but it clearly has one: Why the heck can't these people agree about these fossils that have been out of the ground for thirty years?

The first answer that everyone has given him is about the "million year gap" between 3 million and 2 million years ago. People can't agree about early Homo because they can't decide what its ancestors looked like. Without any ancestors, they don't know which of the traits of early Homo are derived.

For a good example, we can turn to a feature Wilford doesn't mention: limb proportions. Recently, a lot of ink has been spilled discussing the evolution of arm size in later australopithecines and early Homo. OH 62 (probably Homo habilis) and A. africanus have been argued to have large arms compared to their legs. A. afarensis and Nariokotome (KNM-WT 15000, probably Homo erectus) have relatively small arms compared to their legs. Did H. habilis and H. erectus have different ancestors? Did H. erectus evolve from H. habilis, reverting its limb proportions to earlier A. afarensis? Or are all these comparisons just batty, since only three specimens have arm and leg elements whose length can be compared? There's no clear answer; but one of the most important specimens in the question (with sort-of-intermediate limb proportions) is the Bouri skeleton, BOU-VP 12/1, which at 2.5 million years old is right in the middle of that "gap."

The more you look at the "gap," the less gap-like it looks. For one thing, we have a pretty good idea of what was going on behaviorally during that million year span. The first stone tools are 2.6 million years old. The technology of these toolmakers -- although simple -- included all the basic manufacturing methods used before 1.5 million years ago. The tools were used to butcher animals and break bones for marrow; so we know that the toolmakers were depending on meat.

Second, we actually have quite a lot of fossils from this time period. The entire South African A. africanus fossil record, with the exception of a few early specimens like STW 573, come from this "gap." A fairly extensive record of the appearance and evolution of early robust australopithecines comes from this time period in East Africa.

And, here and there, a few specimens look Homo-like. Wilford's article discusses AL 666-1. To this we can add the Uraha mandible, Omo 75-14, an additional series of teeth from Omo, and possibly the Bouri BOU-VP 35/1 skeleton.

Properly considered, the rarity of early Homo in these contexts is not a problem; it is information. Wilford quotes Philip Rightmire to this effect, and we can easily expand on the basic concept. Early toolmakers did not undergo an immediate geographic expansion upon their origin. They spread across a relatively narrow strip of East Africa and stayed there for more than a half-million years. They were initially rare. That means that their adaptation was not immediately a barnburner of a success -- the early toolmakers took a while to perfect the adaptation of later Homo.

The middle part of the article takes in another reason for disagreement: whether H. habilis and H. erectus were ancestor-descendant:

Several scientists, notably Dr. White of Berkeley, took issue with the interpretation seeming to imply that evidence for the two species overlapping in time and exhibiting variable sizes was new. That, he said, had been recognized for a couple of decades.

Dr. Kimbel, who was not involved in the new research, defended the authors, saying that they had not "meant to imply that habilis could not have been ancestral to erectus, presumably on the basis of their being contemporaneous at Turkana," the site in Kenya where the fossils were found.

Susan C. Anton, an anthropologist at New York University who was a member of the Spoor-Leakey team, said, "My money is still on habilis as the potential ancestor, but there is a lot of room for additional knowledge, given the dearth of fossils."

None of these statements really disagree with each other. If anything, this particular question may have gotten easier to resolve lately, not as a consequence of new fossils, but as a result of new dates for many of the old ones. Susan Anton is later quoted saying that anagenesis "is the only option that is no longer on the table," and it seems to me that this is the clearest statement most likely to invite some hypothesis testing. But it is fairly clear that this problem cannot be resolved in terms of earlier fossils: I don't think there's any compelling evidence of H. erectus before 1.6 million years ago.

There is one significant word that doesn't appear in the article -- an absence that is especially interesting considering the quoted scientists:

Remember, the dominant theme is about complexity and bushiness. And yet, here's that forgotten branch of the family tree; the one that was supposed to clarify everything by providing a different ancestor for KNM-ER 1470 from other H. habilis specimens, the one that showed a distinct line leading to Homo originating in the Early Pliocene.

I think our bush may have been pruned.

Appropriate to yesterday's post about the hypothesis of a Eurasian-African clade distinction in early humans, is today's paper from Fred Spoor, Meave Leakey and others, describing the KNM-ER 42700 calvaria and the (unassociated) KNM-ER 42703 maxilla.

The cover photo from the issue is brilliant -- a juxtaposition of KNM-ER 42700 and OH 9 at the same scale:

Press photo, credit: Nature/National Museums of Kenya, F. Spoor and J. Reader

I wrote about KNM-ER 42700 a couple of years ago, when it was shown at the meetings. A few things have changed since then. Most important, the specimen is now accepted as an adult, so that it is assumed to have reached its full adult brain size. That also means that the supraorbital torus, angular torus, and other features reflecting robusticity were probably near their maximum development.

I have much to say about this and the other fossil, which the paper attributes to Homo habilis. The press accounts have all led with the (very) uninteresting and conventional. Here's the AP's Seth Borenstein:

The new research by famed paleontologist Meave Leakey in Kenya shows our family tree is more like a wayward bush with stubby branches, calling into question the evolution of our ancestors.

The old theory was that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became us, Homo sapiens. But those two earlier species lived side-by-side about 1.5 million years ago in parts of Kenya for at least half a million years, Leakey and colleagues report in a paper published in Thursday's issue of the journal Nature.

Here's John Noble Wilford:

Two fossils found in Kenya have shaken the human family tree, possibly rearranging major branches thought to be in a straight ancestral line to Homo sapiens.

Scientists who dated and analyzed the specimens - a 1.44 million-year-old Homo habilis and a 1.55 million-year-old Homo erectus - said their findings challenged the conventional view that these species evolved one after the other. Instead, they apparently lived side by side in eastern Africa for almost half a million years.

Here's Robert Mitchum in the Chicago Tribune:

Two small fossils unearthed in Kenya - the top of a skull, and half of a jawbone - fill an important gap in the evolutionary story of how humans came to be, yet have created as many questions as they have answered.

The similar age and location of the fossils suggest that two early humanlike species, Homo habilis and Homo erectus, closely coexisted rather than coming one after the other on the evolutionary road to modern man, according to a paper published Thursday in the journal Nature.

I could go on. They write themselves, don't they?

But this idea of contemporaneity of H. habilis and H. erectus is neither interesting nor new. Recall yesterday's story about the African and Asian clade hypothesis? News stories had the same lede -- "hominid family tree more complex than thought." This is the ultimate paleontological "dog bites man": "Human Evolution A Bush, Not A Ladder." It's just not interesting anymore.

Why is it old news? Well, we could look back at Bernard Wood's 1991 Koobi Fora monograph, which went into long detail about the assignment of fossils to Homo aff. H. erectus -- fossils that in every case were older than the latest occurrence of Homo habilis at Olduvai.

At least, they thought they were older...

You see, there's some really interesting stories to be told about these fossils. Stories that hasn't appeared anywhere in the press.

Here's a question: Why does that small KNM-ER 42700 skull have all those cranial features from much later, larger, Asian Homo erectus skulls?

Here's what Spoor et al. wrote about it:

The presence of supposedly distinctive 'Asian' characters [18], such as cranial vault keeling and a well separated petrous crest and mastoid process in KNM-ER 42700, underscores the difficulty in separating the African and Asian hypodigms of H. erectus [19]. This difficulty is further accentuated by the observation that the more angulated occipitals and the thicker vaults and supraorbital tori seen in Asian H. erectus are allometric consequences of an increase in cranial size, rather than independent characters (Spoor et al. 2007:689).

Of course, the answer is that they aren't really Asian features. That much is evident from the fact that the later African skulls, OH 9, BOU-VP-2/66 (Daka), and Buia, also have many of them.

KNM-ER 42700 demonstrates that the traits were present in African H. erectus almost from its earliest occurrences. If these early Africans shared the same features as early Asian Homo erectus, then the hypothesis (promoted by many) that these early Africans are themselves an entirely different species, called Homo ergaster must be wrong.

At last, sinking one of those new-fangled bushy human species, and for good? Now, that sounds more like "man bites dog!"

But wait, there's more! Last year, Frank Brown's geochronology group redated many of the early Homo specimens from Koobi Fora, with the surprising result that early Homo erectus no longer included any cranial fossils that were demonstrably older than 1.65 million years. Here's what I wrote at the time:

Looking at what is left in the early part of the sequence is certainly interesting, but just as interesting is how all the H. erectus-like specimens are all bunched together between 1.65 and 1.45 Ma. This is the time interval that already held KNM-WT 15000, KNM-ER 3883, and KNM-ER 42700, and is just older than OH 9. Now we can add KNM-ER 3733, KNM-ER 730, KNM-ER 1808, and KNM-ER 1821. Isn't this an interesting sample? Don't you wish we knew about the other postcrania?

It seems to me that the hypothesis that H. erectus-like hominids first appeared in Africa around 1.65 Ma has interesting archaeological consequences. This isn't long before the appearance of the earliest Acheulean, and it plausibly makes the Developed Oldowan-Acheulean sequence a correlate of this evolution.

It is markedly not coincident with the earliest such evidence in Asia. But that raises the Dmanisi question again, doesn't it?

This is an amazing problem, now. The consensus that Homo habilis and Homo erectus overlapped in time was thrown completely open by the redating. This paper by Spoor and colleagues, by presenting both a new H. erectus specimen and a very late H. habilis specimen, was directed toward this problem. If they are right, it re-establishes the status quo: Homo habilis hung on after the evolution of early Homo erectus, the two species being radically different in their body size (and presumably life history) adaptation, but somehow both making tools and surviving on the same foods.

And yet, this "H. habilis" specimen, KNM-ER 42703, is nearly 200,000 years later than any other member of its species. Almost the only things that makes it H. habilis are its third molars. Are they enough? Or is it Homo erectus, too? Is the overlap completely gone, or will this fossil save it?

And what about that little, tiny, H. erectus skull? At 1.6 million years old, KNM-ER 42700 is a part of the earliest African sample. It's 200,000 years younger than Dmanisi. Did they originate in Asia? Did they evolve directly from their immediate predecessors in Africa, the larger habilines?

You see, this is interesting stuff! It's like a Plio-Pleistocene soap opera -- complete with twins separated at birth, old characters being killed in Amazonian plane crashes and mysteriously returning disguised as someone else.

More tomorrow...

It's a hazardous business, making predictions -- all the moreso because New Year's predictions have a deadline. If they don't happen this year, well, that's too bad, because we'll be checking back a year from now to see how well you did.

Last year, I did pretty well. My 2006 predictions are listed below. I ordered them originally "from most certain to most speculative". As you can see, the first five (i.e., the more "certain" ones) all came true; the last five (i.e., the wild-arsed speculations) didn't. So let's check them out:

• 10. We will see a name for the Flores pathology. OK, we got several names, and the issue is far from settled, but this was the year that the Homo floresiensis doubters struck with their papers on the remains.
• 9. There will be two Neandertal genome-related announcements. I undercalled this, since there were three -- the initial announcement in June of the Neandertal Genome project, the announcement and publication in November of the initial sequence results, and the announcement about possible introgression of microcephalin.
• 8. No Ardipithecus. Sometimes, predictions write themselves.
• 7. "Population cluster" will become the new "race". This one is debatable, but enough papers on multi-ethnic SNPs have used the term this year, that I think it is emerging as the replacement for the race concept for a certain class of geneticists. I expect it will continue -- "cluster" has such a neutral computer-program-centric connotation, that people like to use it.
• 6. There will be another paper (yes, besides the one last month) using genetics to estimate the time of the human-chimpanzee divergence. The date will be 5 million to 7 million years ago. Oh, my. There have been bigger messes than the Patterson et al. 2006 paper, but not many. Yes, it was yet another paper with a 5-million to 7-million-year-old divergence, but it had so much more!
• 5. Evidence of recent selection will be found for several Y chromosome genes. Wishful thinking or prediction for the next year? You decide!
• 4. Sahelanthropus postcrania will be published. This one didn't happen this year, but I'm carrying it over onto the 2007 list.
• 3. There will be an ancient DNA announcement from China. Someday it will happen, but not this year or next.
• 2. StW 573 will be proposed as a new species ancestral to all later hominids. Well, we got the opposite -- with a new younger date, StW 573 was proposed as the ancestor of...nobody! Which was by far the smaller of the redating stories this year.
• 1. A Hawks weblog post will be cited in a peer-reviewed research paper. We can only hope this happens in the coming year, but carrying it over just seems desperate...
• BONUS: A new Georgian hominid will be a robust australopithecine. I still think somebody will find an australopithecine outside Africa in the next decade, but it's not to be from Dmanisi -- the hominids are too localized in a single feature.

So that should give some indication of how to read the list for the next year. I'm listing from more certain to more speculative again, and again I'm excluding most of my own work. The main effect of this is just that I'm not including secrets that I know will be coming out this year. Once again, the predictions are Delphic -- if only I were cleverer, I could make them come out right no matter what!

• 10. Sahelanthropus postcrania will be published.
• 9. Two words: Holocene evolution.
• 8. Despite (or because of) the success of the Neandertal genome project, there will be no genetics of any kind published on early modern skeletal material.
• 7. The mitochondrial history of human dispersals will become more and more detailed, but no paper will test against other loci.
• 6. Another (yes, another) paper about the chimpanzee-human divergence will peg it between 5 and 7 million years ago.
• 5. Three papers with new Ethiopian fossils.
• 4. Another early Upper Paleolithic specimen will emerge from a museum collection.
• 3. A big year for Miocene apes, which will look increasingly important in the story of human brain evolution.
• 2. Maturation rate in early Homo becomes a dead issue, because of the variation in dental and skeletal maturation in living people.
• 1. The year will end without a single new hominid species having been named.
• BONUS: A dramatic development in the problem of pre-2.0-million-year-old Homo.

I ended the year with just a shade fewer than 1 million visits since last January 1. The Neandertal women brought me over 10,000 readers in a single day -- the most ever. I know a few of the big stories from the coming year, but there will be many more that nobody can predict. There's no doubt in my mind that 2007 will be a big year!

In case you haven't been paying attention, the chronology of early African Homo has been completely turned upside-down this year. Well, "upside-down" isn't precisely right; "displaced younger by a quarter-million years" is better.

The redating has come from Frank Brown's group, which in a series of papers has defined and dated stratigraphic units between the major tuffs of the Koobi Fora formation, between the KBS Tuff at 1.87 Ma and the Chari tuff at around 1.38 Ma. Gathogo and Brown (2006) outline the consequences of this redating for fossils of early Homo. Their paper focuses on the fossils from area 123 at Koobi Fora, but discusses the likely consequences of redating on other localities.

Fossils of Homo now estimated to be 1.65 +/- 0.15 myr in age in the Koobi Fora region are currently assigned to at least two taxa on the basis of both crania and mandibles. Homo habilis is represented by specimens KNM-ER 1501, 1502, 1805, and 1813, and H. ergaster is represented by specimens KNM-ER 730, 1812, and 3733 (for attributions, see Wood, 1991, 1992; Wood and Richmond, 2000). The ages of specimens KNM-ER 1501, 1502, 1812, and 1813 have been discussed above, and although not the main focus of this paper, a few notes are offered below on the others.

Specimen KNM-ER 730 derives from a level 5 m below the Koobi Fora Tuff Complex in Area 103 (Feibel et al., 1989), and is thus ca. 1.6 myr old. Feibel et al. (1989) gave an age of 1.85 myr for KNM-ER 1805, but this specimen lies "just below the base of the Okote Tuff" in Area 130 (Leakey et al., 1978), and is more likely closer in age to that of the base of the Okote Tuff Complex (ca. 1.6 myr) than it is to that of the KBS Tuff (1.87 myr). On the basis of mollusc-packed sandstones and algal horizons correlated from Area 102 to Area 104, Feibel et al. (1989) estimated that KNM-ER 3733 was 1.78 myr in age. Although the age of KNM-ER 3733 cannot be confirmed without additional fieldwork, the White Tuff, with an estimated age of 1.63 myr (Brown et al., 2006), is the nearest unequivocally identified unit in the local section in Area 104. This tuff is exposed <300 m from the location of KNM-ER 3733, and Tindall (1985) records only 8 m of section below the White Tuff nearby. Therefore KNM-ER 3733 should be approximately the same age as KNM-ER 1813. Indeed, all specimens from Koobi Fora assigned to H. aff. H. erectus by Wood (1991), many of which are now referred to H. ergaster (Wood and Richmond, 2000), are now estimated to be 1.45 to 1.65 myr old with the exception of KNM-ER 2598. The latter specimen, which is a partial occipital bone from Area 15, was placed 4 m below the KBS Tuff by Feibel et al. (1989) and estimated to be about 1.9 myr old. This age estimate is reasonable because strata do not extend more than 7 m above or below the KBS Tuff at the recorded location of KNM-ER 2598 (Gathogo and Brown 2006:7-8, emphasis added).

This raises a question: Just how much evidence is left for large-bodied H. erectus-like hominids earlier than 1.65 Ma?

Wood (1991) didn't diagnose postcrania, and Gathogo and Brown (2006) don't comment on them. At least KNM-ER 1808 would seem to fall under this umbrella, since Wood (1991) did diagnose that. But more important in bracketing the evolution of large body size is KNM-ER 3228, a hip bone previously dated to 1.95 Ma. It's pretty big for a human, let alone an australopithecine. On the other hand, McHenry and Coffing (2000) suggested that KNM-ER 3228 might belong to H. rudolfensis. To my eyes, this would make it a pretty big specimen compared with femora like KNM-ER 1472 and KNM-ER 1481, but who knows?

Another uncomforable fit in an H. rudolfensis would be KNM-ER 2598. It sure looks like a large-brained, thick-boned specimen. It doesn't look much like KNM-ER 1470. But then, maybe 1470 is the unusual specimen...

Gathogo and Brown (2006) take on directly the issue of KNM-ER 1470 and KNM-ER 1813. The two were formerly considered contemporaries at around 1.89 Ma, but now KNM-ER 1813 is only 1.65 Ma.

KNM-ER 1813, lateral view

The real offshoot of this is that there are no longer any early small-skulled habilines. The question of whether KNM-ER 1470 and KNM-ER 1813 were too different to belong to a single species has drawn a lot of ink, but it was always a non sequitur, because the two weren't the only crania to consider. The more interesting observation had been that Olduvai Gorge preserved only small-skulled habilines, while Koobi Fora had both small and large ones. This was not only a geographic problem but also a temporal one, since the Olduvai habilines were all relatively late (less than around 1.8 Ma) and the Turkana habilines were mostly earlier.

Now the situation has changed. The small Turkana habiline, KNM-ER 1813, is now contemporary with the Olduvai sample. There are no longer any small-skulled early Turkana habilines. KNM-ER 1805 makes sense as a male of the later, small-skulled sample because it is relatively small-brained but robustly built (e.g., with a sagittal crest). That leaves KNM-ER 1470, KNM-ER 1590, KNM-ER 3732, and KNM-ER 3735 as plausible habilines before 1.85 Ma.

This seems like a nice sample as a possible ancestor for both later large-bodied Homo and later habilines. Heck, Wood (1991) even wrote this in his description of KNM-ER 3735:

Some features (e.g. vault thickness) ally it with a Homo erectus-like hominid, but in other areas (e.g. the frontal) it is more like crania such as KNM-ER 1813, a conclusion endorsed by Walker (1987) and by Leakey et al. (1989). Tobias (1989) includes KNM-ER 3735 within H. habilis (Wood 1991:134-135).

What more could you ask of a common ancestor? But then if some of this ancestral population would be expected to resemble later H. erectus-like specimens, then why not KNM-ER 2598?

And what, exactly, would make such a population -- with its mixture of H. erectus-like and habiline-like features -- different from Dmanisi? The answer, of course, is KNM-ER 1470. It's still the odd one in this lineup. But then, it does have the largest brain in this set, which might help to explain the rounded occiput.

Looking at what is left in the early part of the sequence is certainly interesting, but just as interesting is how all the H. erectus-like specimens are all bunched together between 1.65 and 1.45 Ma. This is the time interval that already held KNM-WT 15000, KNM-ER 3883, and KNM-ER 42700, and is just older than OH 9. Now we can add KNM-ER 3733, KNM-ER 730, KNM-ER 1808, and KNM-ER 1821. Isn't this an interesting sample? Don't you wish we knew about the other postcrania?

It seems to me that the hypothesis that H. erectus-like hominids first appeared in Africa around 1.65 Ma has interesting archaeological consequences. This isn't long before the appearance of the earliest Acheulean, and it plausibly makes the Developed Oldowan-Acheulean sequence a correlate of this evolution.

It is markedly not coincident with the earliest such evidence in Asia. But that raises the Dmanisi question again, doesn't it?

References:

Brown FH, Haileab B, McDougall I. 2006. Sequence of tuffs between the KBS Tuff and the Chari Tuff in the Turkana Basin, Kenya and Ethiopia. J Geol Soc 163:185-204.

Gathogo PN, Brown FH. 2006. Revised stratigraphy of Area 123, Koobi Fora, Kenya, and new age estiamtes of its fossil mammals, including hominins. J Hum Evol (in press) DOI link

McDougall I, Brown FH. 2006. Precise ⁴⁰Ar/³⁹Ar geochronology for the upper Koobi Fora Formation, northern Kenya. J Geol Soc 163:205-220.

Wood B. 1991. Koobi Fora Research Project, Volume 4, Hominid Cranial Remains. Clarendon Press, Oxford.

In another post I write about the Martin-Falk exchange on the microcephaly issue.

Here, I review the Paleoanthropology Meetings summary by Elizabeth Culotta in Science.

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.

Der Spiegel is running an interview with Richard Leakey, noted paleoanthropologist and conservationist. The interview covers the Kenya elephant population, the circumstances of early hominid evolution, and dangers to the fossil record.

On the danger of cattle trampling fossils:

Leakey: ... But you are right, the situation is very grave indeed. Koobi Fora, the region you are referring to, is not only a National Park, it was also declared a World Heritage Site back in the early 1970s by Unesco. In spite of this, more and more livestock herders have muscled their way into the Sibiloi National Park with their huge herds of beef cattle. This is where our major excavations are situated. Immeasurable treasures are thus being lost.

On transferring fossils out of Kenya (and Ethiopia) for exhibition:

SPIEGEL: There are currently plans to ship what is perhaps the most well-known and most well-preserved hominid skeleton, the "Turkana Boy" from Kenya and "Lucy," an Australopithecus skeleton from Ethiopia, to museums in the United States and Germany.

Leakey: I consider these plans totally wrong and irresponsible and will do everything in my power to prevent them from happening. I will fight against them. The risk that something could happen to the fossils is too great. They should stay in the countries where they came from. They are extremely fragile. These plans are only about money. In the end, the loser will be science.

SPIEGEL: If Lucy were to spend six years in a glass case in an American museum, thousands of Americans -- rather than just a few researchers -- would be able to see her and marvel at an original hominid...

Leakey: ... which they couldn't differentiate from a copy. Throughout all of those years, any sort of important scientific work would be impossible. Researchers travel here from across the world to work on the find. Scientific innovations continually provide us with new means of analyzing the finds. Paleoanthropology is not a science that ends with the discovery of a bone. One has to have the original to work with. It is a life-long task.

All I can say is, don't ship them to the National Geographic Explorer's Hall -- when I was there, their display of the cast versions made (the very short) Lucy and the (fairly tall) Turkana Boy look the same height. How? The boy's tibiae were sticking through a hole cut in the floor of the display case!

Anyway, a good interview that covers the basics well and updates on Leakey's current work.

One study reported at the meetings brought to mind a growing literature on the sophistication of Pliocene archaeological assemblages, grouped as "Oldowan" or "pre-Oldowan." Most Oldowan tools lack a standardized form, and the assemblages are dominated by flakes, core tools with one sharp edge or point, and unmodified manuports or hammerstones. The lack of standardized tools (such as handaxes) lead easily to the conclusion that Oldowan technical assemblages are simple, so that anyone could make one who could chip rock.

But a number of recent sources illustrate that this perception isn't accurate. The Oldowan encompasses a variation of manufacturing complexity and other elements, but cannot be said to be merely rocks that have been carried or bashed together. The most interesting studies have examined the issue of raw material exploitation and the actual processes used to reduce stone into useful tools.

David Braun gave a presentation that relates to this topic at the 2005 Paleoanthropology Society meetings. In an analysis of the lithic remains at the Kanjera South site (Kenya), the group found that the intensity of the reduction sequence varied with source material.

Kanjera South, dating to around 2.2 million years, preserves one of the largest early records of material culture. According to Plummer et al. (2001:810):

Hominins at Kanjera South utilized a wider variety of lithic raw materials than found at most Oldowan sites, some of which (chert, quartz, quartzite) must have been transported from outside the immediate vicinity of the deposits since they are not present in the local clast population.

In the study by Braun et al. (2005), fine-grained quartzite, which had a nearest source outcrop a long distance away from the site, was reduced more intensively than locally available rock. This reduction involved more flakes taken per core, and occasional retouch. They hypothesized that this difference was due to the hardness of the quartzite and its ability to hold an edge, which makes tools made on quartzite potentially more useful. The hominids apparently recognized these qualities in the raw materials and exploited the quartzite. We can probably infer that the transport distance was a result of this recognition as well.

Stout and colleagues (2005) report on the use of raw materials at Gona, which is at present the earliest site at which stone tools are found, dating to around 2.6 million years. This study sampled unmodified stone taken from conglomerates that represent natural accumulations. If stone were taken merely from local sources without selectivity, the modified stone assemblages from the site would be expected to match these conglomerates. As described by Stout et al. (2005:366-367), the past understanding of Oldowan toolmakers has suggested that they may not have exhibited a clear understanding of the technical qualities of their raw materials:

At Koobi Fora, the high frequency of basalt in local conglomerates (i.e. ancient stream channels) is closely mirrored by its predominance in the artifact assemblages (Toth, 1985; Schick, 1987; Isaac et al., 1997). Although quartz, chert and glassy volcanics are "reasonably easily available" in the conglomerates, these material types do not appear to have been specifically selected for (Isaac et al., 1997:268).

This paper gives an excellent review of the history of raw material choice. In brief, the literature review indicates that early toolmakers at Koobi Fora may have exercised some degree of selectivity by avoiding certain kinds of stone (vesicular lavas and weathered cobbles). By Olduvai Bed II (after 1.7 million years ago), some toolmakers were clearly going out of their way to acquire certain stone materials:

The increased use of chert at Olduvai around 1.65 Myr was clearly occasioned by the temporary exposure of rich sources of this material by the retreating waters of the paleo-lake (Hay 1976). Hominid toolmakers at this time readily appreciated the superior flaking properties of chert, leading to the formation of the earliest known special-purpose quarry site at MNK CFS (Stiles et al. 1974; Stiles 1998) (Stout et al. 2005:367).

So when did this technical knowledge really originate? Was it a skill that developed gradually over the million years between Gona and Olduvai Bed II?

Stout and colleagues find that the materials used for tools at Gona do not match the natural cobbles that were avaiable in a number of respects. In essence, the hominids ignored many kinds of stone that had fracture patterns or other properties that made them less suitable as raw materials. They (2005:368) state the conclusion most clearly at the end of their introduction:

The strong pattern of raw material selection seen at Gona demonstrates that low levels of selectivity are not universal in the Oldowan. The fact that the assemblages from Gona are the oldest known in the world also argues against an overarching temporal trend toward increasing selectivity within the Oldowan.

The flaking skill of early hominids is the subject of a paper by Roche and colleagues (1999) in Science. At the two localities of Lokalalei 1 and 2C, both dating to 2.34 million years ago on the west shore of Lake Turkana, this study accomplished refits of stone flakes and cores to directly inspect the reduction sequence. They found that this sequence was quite complicated in many of the instances of manufacture at the two localities:

At LA2C, the dominant reduction sequence consists of these more reduced cores. Unidirectional or multidirectional removals are flaked on a single debitage surface, from natural or prepared platforms. This knapping system allows the production of a long series of removals without changing the volumetric structure of the core. The repeated application by the knappers of the same technical principles to a whole series of cores, and during the reduction of each core, indicates an elaborate debitage scheme, implying motor precision and coordination. These principles include an appreciation of the quality of the collected raw materials, a judicious exploitation of the natural morphology of the blocks and the maintenance of adequate flaking angles during the entire debitage sequence. These show that the notion of production was already assimilated by a group of hominids in this particular area. This notion is integrated within a real debitage strategy, here well-mastered and unprecedented for this time period (Roche et al. 1999:59).

Upon this description and analysis of the debitage, the study bases the following conclusion:

Overall simplicity and similarities between assemblages are the two main arguments recently put forward to substantiate a technological stasis hypothesis between the 2.6 and 1.6 Myr time periods, and to merge the related assemblages into a single vast 'Oldowan' technocomplex. The stasis hypothesis cannot hold out against the detailed technological analysis of the LA2C lithic assemblage. There can be no doubt about the elaborate character of the LA2C debitage schemes, which are far more sophisticated than at any other Pliocene site (Roche et al. 1999:59).

In total, these studies attest to the technological expertise of some early toolmakers. It is perhaps important to remember that the archaeological record should be expected to reflect an average technical competence much less than that possible (or possibly even typical) of early hominids. For example, every instance of stone flaking by an expert toolmaker certainly was preceded by novice flaking by the same individual earlier in his life. Considering the early mortality evidenced by australopithecine (and early human) remains, many potential toolmakers must have died before reaching proficiency. And toolmaking expertise was probably not uniformly distributed among social groups, so that some individuals had the opportunity to learn by observation some relatively complex reduction sequences and material properties, while others would have had to acquire the same knowledge by long trial and error, if at all.

In this framework, later changes in the archaeological record may reflect social and life history changes as much as ecological changes or brain evolution. Toolmaking intensifies later in the Oldowan, raw material selectivity increases, and some standard forms and more technically sophisticated artifacts, such as bifaces, routinely occur. The increased mental complexity of Pleistocene hominids may be a cause, but the behavioral changes have no obvious anatomical, life history, or other correlate. The apparent sophistication of the earliest toolmakers argue against the hypothesis that the later Oldowan represents a fundamentally more intelligent hominid species, with specialized adaptations to tool manufacture lacking in earlier hominids. Instead, I would suggest that later Oldowan hominids had on average a greater retention of cultural knowledge as a function of more stable groups and a longer life history than australopithecines. This shift might or might not have been accompanied by an increase in the capacity to learn, as might be evidenced by a greater length of the juvenile growth period.

From a conceptual perspective, there is necessarily a real limit on the standardization that is possible within any "technocomplex," and particularly one that spans a million years or longer. The kind of information that is ultimately transmissible (either horizontally or vertically) among hominids over this extreme time period is of the most rarified form imaginable. A model of early archaeological assemblages that incorporated the probable manner and form of information transfer among groups (along with their global demography) would predict both a global lack of complexity and a great extent of variability within that simple context. The evidence of technical skills therefore may inform directly about the demography of groups and their relationships with each other. The extent to which such variability may be consistent with cultural diffentiation among groups in other primate species (such as chimpanzees) I take to be a testable hypothesis.

References:

Most references within the featured articles below:

Plummer T, Ferraro J, Ditchfield P, Bishop L, Potts R. 2001. Late Pliocene Oldowan excavations at Kanjera South, Kenya. Antiquity 75:809-810.

Roche H, Delagnes A, Burgal JP, Feibel C, Kibunjia M, Mourre V, Texler PJ. 1999. Early hominid stone tool production and technical skill 2.34 Myr ago in West Turkana, Kenya. Science 399:57-60.

Stout D, Quade J, Semaw S, Rogers MJ, Levin NE. 2005. Raw material selectivity of the earliest stone toolmakers at Gona, Afar, Ethiopia. J Hum Evol 48:365-380.

One study reported at the meetings brought to mind a growing literature on the sophistication of Pliocene archaeological assemblages, grouped as "Oldowan" or "pre-Oldowan." Most Oldowan tools lack a standardized form, and the assemblages are dominated by flakes, core tools with one sharp edge or point, and unmodified manuports or hammerstones. The lack of standardized tools (such as handaxes) lead easily to the conclusion that Oldowan technical assemblages are simple, so that anyone could make one who could chip rock.

But a number of recent sources illustrate that this perception isn't accurate. The Oldowan encompasses a variation of manufacturing complexity and other elements, but cannot be said to be merely rocks that have been carried or bashed together. The most interesting studies have examined the issue of raw material exploitation and the actual processes used to reduce stone into useful tools.

David Braun gave a presentation that relates to this topic at the 2005 Paleoanthropology Society meetings. In an analysis of the lithic remains at the Kanjera South site (Kenya), the group found that the intensity of the reduction sequence varied with source material.

Kanjera South, dating to around 2.2 million years, preserves one of the largest early records of material culture. According to Plummer et al. (2001:810):

Hominins at Kanjera South utilized a wider variety of lithic raw materials than found at most Oldowan sites, some of which (chert, quartz, quartzite) must have been transported from outside the immediate vicinity of the deposits since they are not present in the local clast population.

In the study by Braun et al. (2005), fine-grained quartzite, which had a nearest source outcrop a long distance away from the site, was reduced more intensively than locally available rock. This reduction involved more flakes taken per core, and occasional retouch. They hypothesized that this difference was due to the hardness of the quartzite and its ability to hold an edge, which makes tools made on quartzite potentially more useful. The hominids apparently recognized these qualities in the raw materials and exploited the quartzite. We can probably infer that the transport distance was a result of this recognition as well.

Stout and colleagues (2005) report on the use of raw materials at Gona, which is at present the earliest site at which stone tools are found, dating to around 2.6 million years. This study sampled unmodified stone taken from conglomerates that represent natural accumulations. If stone were taken merely from local sources without selectivity, the modified stone assemblages from the site would be expected to match these conglomerates. As described by Stout et al. (2005:366-367), the past understanding of Oldowan toolmakers has suggested that they may not have exhibited a clear understanding of the technical qualities of their raw materials:

At Koobi Fora, the high frequency of basalt in local conglomerates (i.e. ancient stream channels) is closely mirrored by its predominance in the artifact assemblages (Toth, 1985; Schick, 1987; Isaac et al., 1997). Although quartz, chert and glassy volcanics are "reasonably easily available" in the conglomerates, these material types do not appear to have been specifically selected for (Isaac et al., 1997:268).

This paper gives an excellent review of the history of raw material choice. In brief, the literature review indicates that early toolmakers at Koobi Fora may have exercised some degree of selectivity by avoiding certain kinds of stone (vesicular lavas and weathered cobbles). By Olduvai Bed II (after 1.7 million years ago), some toolmakers were clearly going out of their way to acquire certain stone materials:

The increased use of chert at Olduvai around 1.65 Myr was clearly occasioned by the temporary exposure of rich sources of this material by the retreating waters of the paleo-lake (Hay 1976). Hominid toolmakers at this time readily appreciated the superior flaking properties of chert, leading to the formation of the earliest known special-purpose quarry site at MNK CFS (Stiles et al. 1974; Stiles 1998) (Stout et al. 2005:367).

So when did this technical knowledge really originate? Was it a skill that developed gradually over the million years between Gona and Olduvai Bed II?

Stout and colleagues find that the materials used for tools at Gona do not match the natural cobbles that were avaiable in a number of respects. In essence, the hominids ignored many kinds of stone that had fracture patterns or other properties that made them less suitable as raw materials. They (2005:368) state the conclusion most clearly at the end of their introduction:

The strong pattern of raw material selection seen at Gona demonstrates that low levels of selectivity are not universal in the Oldowan. The fact that the assemblages from Gona are the oldest known in the world also argues against an overarching temporal trend toward increasing selectivity within the Oldowan.

The flaking skill of early hominids is the subject of a paper by Roche and colleagues (1999) in Science. At the two localities of Lokalalei 1 and 2C, both dating to 2.34 million years ago on the west shore of Lake Turkana, this study accomplished refits of stone flakes and cores to directly inspect the reduction sequence. They found that this sequence was quite complicated in many of the instances of manufacture at the two localities:

At LA2C, the dominant reduction sequence consists of these more reduced cores. Unidirectional or multidirectional removals are flaked on a single debitage surface, from natural or prepared platforms. This knapping system allows the production of a long series of removals without changing the volumetric structure of the core. The repeated application by the knappers of the same technical principles to a whole series of cores, and during the reduction of each core, indicates an elaborate debitage scheme, implying motor precision and coordination. These principles include an appreciation of the quality of the collected raw materials, a judicious exploitation of the natural morphology of the blocks and the maintenance of adequate flaking angles during the entire debitage sequence. These show that the notion of production was already assimilated by a group of hominids in this particular area. This notion is integrated within a real debitage strategy, here well-mastered and unprecedented for this time period (Roche et al. 1999:59).

Upon this description and analysis of the debitage, the study bases the following conclusion:

Overall simplicity and similarities between assemblages are the two main arguments recently put forward to substantiate a technological stasis hypothesis between the 2.6 and 1.6 Myr time periods, and to merge the related assemblages into a single vast 'Oldowan' technocomplex. The stasis hypothesis cannot hold out against the detailed technological analysis of the LA2C lithic assemblage. There can be no doubt about the elaborate character of the LA2C debitage schemes, which are far more sophisticated than at any other Pliocene site (Roche et al. 1999:59).

In total, these studies attest to the technological expertise of some early toolmakers. It is perhaps important to remember that the archaeological record should be expected to reflect an average technical competence much less than that possible (or possibly even typical) of early hominids. For example, every instance of stone flaking by an expert toolmaker certainly was preceded by novice flaking by the same individual earlier in his life. Considering the early mortality evidenced by australopithecine (and early human) remains, many potential toolmakers must have died before reaching proficiency. And toolmaking expertise was probably not uniformly distributed among social groups, so that some individuals had the opportunity to learn by observation some relatively complex reduction sequences and material properties, while others would have had to acquire the same knowledge by long trial and error, if at all.

In this framework, later changes in the archaeological record may reflect social and life history changes as much as ecological changes or brain evolution. Toolmaking intensifies later in the Oldowan, raw material selectivity increases, and some standard forms and more technically sophisticated artifacts, such as bifaces, routinely occur. The increased mental complexity of Pleistocene hominids may be a cause, but the behavioral changes have no obvious anatomical, life history, or other correlate. The apparent sophistication of the earliest toolmakers argue against the hypothesis that the later Oldowan represents a fundamentally more intelligent hominid species, with specialized adaptations to tool manufacture lacking in earlier hominids. Instead, I would suggest that later Oldowan hominids had on average a greater retention of cultural knowledge as a function of more stable groups and a longer life history than australopithecines. This shift might or might not have been accompanied by an increase in the capacity to learn, as might be evidenced by a greater length of the juvenile growth period.

From a conceptual perspective, there is necessarily a real limit on the standardization that is possible within any "technocomplex," and particularly one that spans a million years or longer. The kind of information that is ultimately transmissible (either horizontally or vertically) among hominids over this extreme time period is of the most rarified form imaginable. A model of early archaeological assemblages that incorporated the probable manner and form of information transfer among groups (along with their global demography) would predict both a global lack of complexity and a great extent of variability within that simple context. The evidence of technical skills therefore may inform directly about the demography of groups and their relationships with each other. The extent to which such variability may be consistent with cultural diffentiation among groups in other primate species (such as chimpanzees) I take to be a testable hypothesis.

References:

Most references within the featured articles below:

Plummer T, Ferraro J, Ditchfield P, Bishop L, Potts R. 2001. Late Pliocene Oldowan excavations at Kanjera South, Kenya. Antiquity 75:809-810.

Roche H, Delagnes A, Burgal JP, Feibel C, Kibunjia M, Mourre V, Texler PJ. 1999. Early hominid stone tool production and technical skill 2.34 Myr ago in West Turkana, Kenya. Science 399:57-60.

Stout D, Quade J, Semaw S, Rogers MJ, Levin NE. 2005. Raw material selectivity of the earliest stone toolmakers at Gona, Afar, Ethiopia. J Hum Evol 48:365-380.