Olduvai Gorge

I've just been reading a useful paper by Andrew Millard, which reviews the chronometric dates of African and Near Eastern fossil hominids from the Middle and early Late Pleistocene. The overall theme is that we don't know the dates nearly as well as we would like -- or as well as many comparative analyses have assumed.

The highlight is the list of specimens with primary references to different date estimates. Anyone with a good training in paleoanthropology probably has a feel for which specimens have relatively good dates and which are real hands-up-in-the-air cases. Kabwe makes for a good example of the latter:

Kabwe (Broken Hill), Zambia. The remains of "Rhodesian Man," along with faunal remains, were discovered in 1921 by miners (Klein, 1973). The principal dating is based on Klein's (1973) assessment that the fauna is similar to that at Elandsfontein and broadly similar to those from Olduvai Gorge Upper Bed II through to Bed IV. There are no chronometric determinations. On the basis of the faunal correlation to Olduvai (Fig. 1), an age of younger than 1780 ka and, depending on the chronology for Olduvai, either older than 990 ka (on the long chronology) or, more likely, older than 490 ka (on the short chronology) may be assigned (see under Olduvai above). This is consistent with Elandsfontein being older than 330 ± 6 ka (Table 1).

Millard's discussion of "chronometric hygiene" takes up much of his discussion. This is nothing more than the simple idea that we should weed bad dates out of our analyses. For example, he singles out Florisbad as a specimen that has been handled poorly in the literature:

Use of the literature. In conducting this review of the chronometric evidence for African and Near Eastern hominids, the search for the detailed chronometric data was hampered by overreliance of many authors on the secondary literature. It is not uncommon to find a date cited from a publication, which upon checking simply cites another publication, which cites another, which cites the paper that first suggested the date. Frequently in such a chain of citations, the justification for the original date is lost, and in some cases, error limits disappear. For example, the ESR date of 259 ± 35 ka for the Florisbad hominid (Grün et al., 1996) can be applied to the Florisbad fauna, but somehow in the discussion of Stynder et al. (2001), this becomes simply "a maximum age of around 250 ka" (p. 372) for the Florisbad Faunal Span, and in McBrearty and Brooks (2000), it becomes a bald 260 ka age without any uncertainty for the Florisbad hominid itself. Sometimes, the primary proposal for a date is based solely on comparisons of morphology to the best-dated fossils at the time of publication, and for later papers to suggest evolutionary sequences based on this date is obviously problematic. Given the flux in dating methods, the fact that problems have often been identified some time after the introduction of these methods, and the changing understanding of the dates of faunal successions, every author should be beholden to check the basis of the dates cited and apply some basic chronometric hygiene (Millard 2008:19).

Of course, there is an irony here, since Millard's effort has generated a massive secondary source listing date estimates for all these hominids! I agree whole-heartedly with his sentiment, though -- everyone should do a better job of reading and citing papers.

But the effect of all this hygiene is to emphasize that most of the Middle Pleistocene remains a muddle, with very few well-resolved dates across the entire span. Millard describes faunal correlations as a relatively weak source of evidence in Africa. Above the time span effectively covered by ESR/TL, there is little to rely on.

References:

Millard AR. 2008. A critique of the chronometric evidence for hominid fossils: 1. Africa and the Near East 500-50 ka. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.11.002

After my Q and A with paleoanthropologist Mica Glantz, I got a lot of great response -- people really liked reading about work in the field from somebody other than me!

So, I'm going to make these interviews a regular feature. When I was in Michigan last week, I got a chance to talk with Adam Van Arsdale, who graciously agreed to answer some questions about his work.

UPDATE(11/29/2007): After posting, I heard from a reader who reminded me that I omitted Adam's affiliation and info! Adam is a lecturer in anthropology at the University of Michigan. You can find out more about his interests on his webpage.

Hawks: You were lucky enough to work at one of today's most exciting paleoanthropological sites, Dmanisi. What can you tell us about your experience there?

Van Arsdale: Dmanisi is a wonderful place and I can't say enough positive things about the site and all the people I have worked with through the project. To begin, the site itself is just a nirvana for anyone with an interest in history or prehistory. The primary excavation area is in the middle of a ruined medieval citadel complex which rose to prominence as a trading town along the silk road; down from the promontory are the tombs of Mongols who sacked the city in the 12th century; further down are early Christian burials, and along the river are the remains of bath houses for travelers along the Silk Road. It is a literally a place where time seeps out of the ground.

Leaving the setting aside, the people associated with the project have been wonderful to work with. The size of the excavation team would vary but there would be times when, at the end of a long excavation day, I would find myself sitting at a long dinner table surrounded by 40 people speaking more than half a dozen languages. In the years I worked there as a graduate student I think we had students and researchers from 15 different countries (and I'm probably missing a few). Everyone who works at the site, including the local residents of Patara Dmanisi, adds their own character to the project. As a graduate student, my summers at Dmanisi served as something of a Paleoanthropology bootcamp, with regular discussions and debates between all of us with very different training and different theoretical perspectives on the issues of human evolution.

And then on top of all of this there are, of course, a remarkable set of fossils and archaeological materials.

Hawks: Do you want to give a shout-out to anybody in Georgia?

Van Arsdale: There are too many to name, but certainly David Lordkipanidze, who first invited me to Dmanisi in 2001, deserves recognition. I'll also add Gocha Kiladze, Teona Shelia and Dato Zhvania, who began working at Dmanisi in 1991 as students and who continue to play a significant role in the operation of the site today. One of the great things about the site is that it has served as a tremendous springboard for Georgian students interested in paleoanthropology. I think it is a safe bet we will be hearing a lot from our Georgian colleagues in the years ahead.

Hawks: Your dissertation work focused on the Dmanisi mandibles. I know that you still have publications coming out on these, so feel free to keep quiet about anything you're saving for print. What can you tell us about the sample?

Van Arsdale: The Dmanisi mandibles are a remarkable sample. They show a huge amount of morphological variation in a set of fossils derived from a temporally and geographically constrained set of deposits. One of the mandibles is in many characters the largest mandible assigned to the genus Homo. Two of the others are quite small, with variably large and small teeth. And the fourth specimen is one of the earliest edentulous mandibles in the hominid record. Given the current season, it is perhaps appropriate to describe the sample as a real cornucopia of variation. And the location and date of the site itself is surprising. Dated to 1.8 million years and about 2000 miles from the outlet of the rift valley in northeast Africa, the site is a long way from the contemporaneous and well-known deposits from the Turkana Basin in Kenya and Olduvai Gorge in Tanzania.

So how do we account for all this variation? That was basically the question of my dissertation. I sought to answer this question by testing a series of hypotheses focused first on sources of intraspecific variation, particularly age and sexual dimorphism, then secondarily on hypotheses of interspecific differentiation (i.e. multiple species). I then evaluated the results of these quantitative tests in the context of the comparative anatomy of the Dmanisi sample. Sparing you all the details, I think there are strong reasons to consider the Dmanisi hominid sample as that of a single species, but one displaying considerable amount of variation associated with age and possibly elevated levels of sexual dimorphism relative to what we observe in contemporary and recent human populations.

Hawks: Of course, your work required a lot of comparisons with other samples, and mandibles are among the most common skeletal elements represented in the fossil record. How did you handle your comparative work?

Van Arsdale: Paleoanthropology is at its root a comparative discipline. It is difficult to interpret any set of fossils outside of some comparative model. My work is no different. In asking questions about variation associated with age and sex, my dissertation is really asking how strange (or not strange) does the variation in the Dmanisi sample look if we treat it like a mixed age and sex sample of humans? Of chimpanzees? Of gorillas? Each of these species possess somewhat differing patterns of variation so that our final understanding of the Dmanisi specimens is based on a combination of similarities and differences with these different comparative models.

You can also try to understand the sample from the perspective of other fossils. These comparisons are more challenging because we have less certainty regarding the things we think we know about fossils. For example, in my dissertation I also make a series of comparisons between the Dmanisi mandibles and a sample of Australopithecus boisei mandibles from East Africa. It is much more difficult to say for certain whether any given fossil specimen is male or female, and in the absence of well preserved teeth, young or old. That uncertainty limits the power of the hypothesis tests we can bring to the question by limiting the amount of information we have to work with.

One of the exciting aspects of Paleoanthropology's comparative perspective is that new fossils give us new ways of looking at old fossils. Possibly the most exciting aspect of the Dmanisi fossils is that they provide us a tremendous platform from which to look back at these large samples from East and Southern Africa that we have known about for a long time and reexamine questions which had either previously been unanswerable or whose accepted answers no longer seem so clear.

Hawks: Any stories you can share about your travels?

Van Arsdale: One of the more unique experiences from my travels occurred while I was tagging along with a graduate student from Yale on her project involving 4.5 million year old fossil exposures in the Tugen Hills of the Central Rift Valley, Kenya. I was off on my own one day, walking along one of the exposures when I came across what appeared to be part of a fossilized crocodile skull just barely sticking out of the ground. I sat down and began very carefully exposing its boundaries so that it could be properly prepared and taken out. After about 20 minutes of this, a young Tugen boy came out of the bushes and sat down next me and began watching me work. I tried to say a few words of greeting in my very rudimentary Kiswahili, but either my pronunciation was too terrible to be understand (quite likely) or he was too young to have yet learned Kiswahili (he looked like he was between 8 and 10). After a few more minutes the boy, who had been carrying a small bow and set of arrows, took out one of his arrows and began using its steel tip as a mini-trowel. I would have discouraged him out of fear he might damage the fossil or go on trying to dig up other fossils in the area, but as I watched him he was exceedingly careful and seemed completely enraptured by the work. It was just one of those moments where, while the event was going on, I recognized how amazingly unique it was. Here we were, a graduate student from the University of Michigan with twenty plus years of formal education and a young Tugen boy with at most a few years of schooling, sitting side by side on a hillside in the middle of Kenya carefully exposing a 4.5 million year old fossil. The only common language between us was the action of my Marshalltown trowel and his handmade arrow point and a basic curiosity in this fossil.

Hawks: It's a story you hear from students a lot: teeth and mandibles are "bor-ing". But of course, they're the best representatives of variation we have through much of human evolution -- if you want to study evolution, you'll be studying jaws and teeth. What keeps these questions exciting for you?

Van Arsdale: One of the reasons I enjoy looking at mandibles and teeth are that they can potentially provide a window into numerous aspects of human evolution. As you point out, they are the most abundant element in the fossil record and therefore provide a large set of data with which to address questions of evolutionary relationships and evolutionary change. They can also tell you something about the ecology and diet of the individual specimen. Finally, they tell us something about how an organism develops throughout life and ages.

This also means that questions regarding variation in jaws and teeth can be difficult to answer because many different processes might account for the observed variations. When testing hypotheses about mandibular variation it is important to keep this in mind. It is always striking to me how many hominid type specimens are or have served at some time as type specimens for a new species. This is in part a reflection of their relative abundance, but I think it also reflects how difficult it is to adequately address all the potential sources of variation in mandibles. If you accept the conclusions of my research, the Dmanisi mandibles serve as a cautionary tale in this regard.

Hawks: Some readers may know that you and I share the same graduate advisor, Milford Wolpoff, who has certainly been a strong influence on the way I approach evolutionary questions. But I also find myself going back to other people who influenced my training. Who/what really got you interested in the field, or shaped the way you think about evolution?

Van Arsdale: I initially entered anthropology by happy circumstance. Entering college (Emory University) I was interested in majoring in both English Literature and Evolutionary Biology. My first year two things happened; I realized Emory's biology department was primarily focused on microbiology and full of pre-med students (something I was not interested in) and I took my first Anthropology course to fulfill a distribution requirement. I was immediately hooked. Here I could have the best of both worlds... an integrative approach towards understanding what it means to be human and a careful examination of the evolutionary processes which have shaped the pattern of human evolution. I owe a huge part of my perspective to Milford and the other faculty and students I worked with as a graduate student, but I don't think I fully realized the influence my undergraduate teachers had on my perspective till the AAA meetings last year when I was able to attend a session honoring the graduate advisor (Jack Kelso) of my undergraduate advisor (George Armelagos). I listened to talks by people I had never met, but with whom I share some of my academic phylogeny, and what I heard were familiar themes on the interaction of human biological and cultural processes. This bio-cultural perspective is something I carry with me from Emory and is evident in the approach I take towards questions of Pleistocene human evolution, where changes in human skeletal form cannot be understood outside of the context of our ever-expanding brains and the increasingly complex ways in which we interact with the people and environments around us. Now that I am teaching, it is something I am aware of when I am in front of the undergraduates in my own classes.

Hawks:Some of your current research involves a lot of genetic modeling. How did you get into this area? Can you tell us about some of your thoughts?

Van Arsdale: My interest in genetic modeling first began as an undergraduate. In part it reflects my status as an admitted math nerd. I like numbers, I like using computationally intense models and simulations to address specific hypotheses, and I like understanding how evolutionary and cultural processes interact in dynamic ways. But when I was an undergrad my interest in genetic models stemmed out of my interest in modern human origins and the belief that any really good model should be able to simultaneously explain the pattern of fossil, archaeological, and genetic evidence. At the time there was quite a bit of discussion not just about how the increasing amount of genetic data related to previously held understandings of the fossil and archaeological record, but also how compatible data from different genetic systems were with each other. In particular, data from non-recombinant genetic systems (mtDNA and parts of the Y-chromosome) seemed to provide a different picture of human evolution than data from recombinant genetic systems. My attempt to understand these differences is what really drew me into aspects of genetic modeling.

Since that time my interest genetic modeling has really developed out of what I consider an anthropological approach towards understanding genetic systems. I like to quote one of the take-away messages from the dissertation defense of another Michigan graduate, Keith Hunley, who modeled genetic aspects of South American population structure in his dissertation. As Keith said in his defense, what people do matters. Most genetic models are dependent on a variety of demographic parameters (population size, structure, etc.), all those things that people do. And yet most geneticists do not, or simply cannot directly address these demographic parameters with the data available to them. As a paleoanthropologist, one role my research serves is to provide better understandings of what people did and the ways in which they interacted in the past so as to better inform such genetic models.

On a more theoretical level I am very much interested in exploring how the unique ways in which humans shape and interact with our evolutionary landscape serves to structure genetic variation and the evolutionary forces which shape it.

Hawks: What's the next step for you? Where do you go from here with your research?

Van Arsdale: Most of the questions I am working on now reflect my current thinking that the basic pattern which characterizes Pleistocene human evolution; the complex interaction between increasing cultural complexity, expanding ecological niches, and basic anatomical changes (encephalization, dental reduction); establishes itself early in the Pleistocene if not prior than that. Essentially, that sometime around 2-2.5 million years ago a group of hominids stopped acting like bipedal apes (the Australopithecines) and started acting human. This basic human pattern then continued to develop and characterize Pleistocene hominids until about 10-20,000 years ago when we stopped acting like humans and started acting like domesticated humans.

By understanding how this pattern manifests itself early in the Pleistocene, for example, by considering how, why and with what changes human populations expanded into places like Southern Georgia as early as 1.8 million years ago, you can develop broader understandings of the Pleistocene as a whole. I am just finishing up two projects related to this broad topic, one examining the Habiline-Erectine transition in the Lower Pleistocene and another attempting to characterize broad demographic changes within the Pleistocene.

I also want to continue my involvement in paleoanthropological field work and would like to continue examining Plio-Pleistocene deposits in Western and Central Asia. Dmanisi is an incredible site and has provided a great amount of detailed evidence to address questions of human evolution from this time period. But the detailed picture it provides encompasses only a narrow range of time and space...the more we can expand that window the better we can understand the broad patterns of change which characterize humans in the Plio-Pleistocene.

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...

Rex Dalton reports in this week's Nature on permit problems in Olduvai Gorge:

For 18 years, the Olduvai Landscape Paleoanthropology Project (OLAPP) -- led by anthropologist Robert Blumenschine of Rutgers University in New Brunswick, New Jersey, archaeologist Fidelis Masao of the University of Dar es Salaam and Jackson Njau, principal curator at Tanzania's National Natural History Museum in Arusha -- has collected plant and animal specimens to learn how these early relatives of man lived in the region (R. J. Blumenschine et al. Science 299, 1217-1221; 2003).

Last summer, the OLAPP team was distressed to learn that Tanzanian officials had issued permits to a group led by Manuel Domínguez-Rodrigo, of Complutense University in Madrid, and Audauz Mabulla, of the University of Dar es Salaam, to dig within the OLAPP region. The OLAPP researchers then found the competing group a kilometre away from their campsite, probing trenches the OLAPP team had dug near the bed where Leakey uncovered 'Zinj', the original P. boisei skull.

I don't know anything about the details of this dispute, but the article seems to tilt toward the OLAPP point of view. It quotes Domínguez-Rodrigo, but doesn't really provide any detail that might support his team's point of view.

The article does provide some details intended to undercut the claims that others claimed they made, but they claim they didn't claim. You follow? Me neither. It's a short he said, he said kind of article that doesn't do anything but flag a "controversy." These kinds of articles always irritate me.

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 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.

The History Channel is showing its new human evolution program, "Ape to Man" this Sunday, August 7, at 9:00 EDT / 8:00 CDT. The show has a website, which gives the list of interviewees (Leslie Aiello, Joe Cain (history of science), Chris Stringer, and Colin Menter (fossil sites of South Africa). There is also a quick synopsis:

Highlights of APE TO MAN include:

Reenactments of the work of Eugene DuBois, an Amsterdam physician who left his practice in 1890 in search of the Missing Link and found what would be called Homo erectus, a 500,000-year old ape-like skeleton, in Sumatra. DuBois' assertion that he has found the Missing Link results in his rejection by the scientific community. Only later did people realize the impact of the discovery.

Examination of the key elements that marked the evolution from ape to man, including the ability to walk upright, the use of tools, the harnessing of fire, the ability to form communities, and the ability to reason and plan.

The story of Piltdown Man, a skeleton discovered in England in 1912 which was, for a time, considered by many to be the definitive Missing Link, but later discovered to be one of the greatest hoaxes in the history of science.

Raymond Dart's 1924 discovery of Taung Child, a fossilized brain in Africa, nearly two million years old. It was the oldest finding to date, but was completely ignored by the scientific community because people still believed in the erroneous story of Piltdown Man.

The two key shifts in thinking that led to our understanding today: the shift to Africa as the birthplace of the human species and the shift from the thinking that brain size was the driving force of evolution, to the understanding that the use of tools was really the key step.

The online preview shows a Dalmatian running in front of a Land Rover, so I assume they'll have reenactments of the Leakeys also.

I found the online game to be strangely entertaining, since you have to navigate a little Indiana Jones-looking archaeologist around his campsite to find fossils, while avoiding spiders, bees, and quicksand, and returning to the water bucket every couple of minutes for a drink. Of course, when you do it the third time around, and "Zhoukoudian" looks exactly like "Olduvai Gorge" except with more spiders and bees, well, you get the picture. The "quiz" I found less entertaining since several of the questions give out slightly wrong information, and one is really wrong (Dubois' Trinil discovery is around a million years old, not 50,000, in case you're wondering).

But at the end of the game, there is a cool newspaper, with the headline, "MISSING LINK FOUND!", a photo of the Bone Clones version of Toumaï, and the story:

One of the greatest riddles in human history has been solved after leading anthropologist Dr. John Hawks found The Missing Link in human evolution. The discovery came after a grueling quest that spanned three continents, and tested the very limits of human endurance.

Almost enough to get me to watch!

Michelle Drapeau and colleagues (2005) report on the AL 438-1 specimen from Hadar. The specimen consists of "part of the mandible, a frontal bone fragment, a complete left ulna, two second metacarpals, one third metacarpal, plus parts of the clavicle, humerus, radius, and right ulna" (1). At 3 million years, the specimen is one of the youngest of the A. afarensis sample.

The AL 438-1 individual was evidently relatively large compared to the rest of the Hadar sample. The ulna length is 278 mm, which is larger than the mean for any of the human samples examined by Aiello et al. (1999) in their comparative study of the OH 36 ulna. It is about average for a chimpanzee, although chimpanzees have relatively longer forelimbs than would have been true of A. afarensis, so again this is evidence of a relatively large body size.

Drapeau et al. (2005) make a point of the proportion of the ulna and the mandible being similar to that found in AL 288-1 (Lucy), which they take as evidence that large teeth in this late specimen may be attributed to larger body size rather than greater megadonty:

Both Australopithecus afarensis mandibles have a larger corpus (breadth and height at M₁ relative to the ulnar size surrogate than those of African apes. Similarly, mandibular corpus shape (breadth/height x 100 at M₁) is similar in the two fossils (A.L. 288-1, 57%; A.L. 438-1, 60%). This difference in mandibular size corresponds to what would be expected from two extant ape conspecifics with ulnae of such different sizes. Since there are no differences between the two Hadar skeletons in mandibular to ulnar proportions, there is no evidence for an increase in mandibular size relative to the rest of the skeleton between the points in time represented by these two individuals. We cautiously offer this as support for Lockwood et al.'s (2000) suspicion that the observed temporal trend toward larger mandible size reflects a body size increase late in the Hadar time span of A. afarensis (Drapeau et al. 2005:41-42).

The paper has a substantial discussion of the morphology and comparative anatomy of the ulna. The bottom line of this analysis is that the ulna is similar to that of AL 288-1 in most respects, except for its larger size and somewhat greater curvature. It is, however, smaller and somewhat less curved than the later Omo L40-19, and substantially less curved than the OH 36 ulna. The authors write this about its similarities to other homionids:

While phenetically A.L. 438-1 presents a mix of ape-like and human-like morphology, when considered in a phylogenetic context, the Australopithecus afarensis forelimb shares synapomorphies exclusively with humans among extant hominoids taxa. It resembles non-hominins only in plesiomorphic character states. In this context, it is apparent that A. afarensis forelimb anatomy reveals the results of selection for a more human-like humeroulnar joint, larger thumbs, and altered carpometacarpal joints that reflect an emphasis on manipulative aptitude at the expense of forelimb-dominated climbing ability (Drapeau et al. 2005:43).

That is a relatively powerful statement of the adaptive qualities of the A. afarensis forelimb, which appers more or less necessary to explain the differences between early hominids and apes in this respect. If the early hominids were really climbing a substantial proportion of the time, then we might hypothesize that their forelimbs ought to look more like ape arms. But they don't; there are clear differences that make the early hominid arms look more similar to human arms. Thus, the authors turn to the hypothesis that the A. afarensis forelimb is additionally adapted to "an emphasis on manipulative aptitude."

At the moment, this hypothesis remains to be strongly tested. Most of the human-like features of the A. afarensis arm are arguably the result of not being used in quadrupedal weight support. Thus, the fact that "the Australopithecus afarensis elbow joint appears to reflect habitual loading the elbow at or near 90 degrees, rather than optimization for loading in a more extended posture as in extant apes" (43-44), as well as the anatomy of the joint and the form of the carpometacarpal joints may all be explained by the fact that early hominids were not knuckle (or fist) walkers. The large thumbs are the strongest piece of evidence for any kind of manipulative behavior in A. afarensis.

On the subject of retained similarities with apes, Drapeau et al. (2005:46) have this to say:

The retention of African ape symplesiomorphies in A. afarensis may be attributed to either stabilizing selection fore a partially arboreal locomotor repertoire, or to lack of selection against these traits (see discussion in Stern, 2000; Ward, 2002). It is inherently difficult to test these alternative hypotheses. Thus, the significance of these retained traits for reconstructing the behavior of A. afarensis is difficult to determine with certainty in the context of demonstrable selection for a human-like elbow and hand joints. Australopithecus afarensis shares some apomorphies with humans that suggest emphasis on use of the forelimb in flexed postures, and improved grip capability relative to apes. The presence of these synapomorphies suggests similarities in forelimb function among hominins, likely reflecting selection for expanded manipulative capabilities and flexed forearm postures relative to that found in apes and a diminished capacity for ape-like arboreal behaviors. Only later did humans display evidence of further selection for manipulation coupled with reduced forelimb robusticity. We conclude that in Australopithecus afarensis, selection for natural manipulation outweighed selection for arboreal activities, but that selection for refined manipulative ability had not yet come into play in human evolution.

A fine balance, if it is true, and fitting within the generally understood picture that, with regard to its arm and hand functions, A. afarensis was either Homo habilis nor a chimpanzee.

References:

Aiello LC, Wood B, Key C, and Lewis M. 1999. Morphological and taxonomic affinities of the Olduvai Ulna (OH 36). Am J Phys Anthropol 109:89-110.

Drapeau MSM, Ward CV, Kimbel WH, Johanson DC, and Rak Y. 2005. Associated cranial and forelimb remains attributed to Australopithecus afarensis from Hadar, Ethiopia. J Hum Evol Advance before print.

Lockwood CA, Kimbel WH and Johanson DC. 2000. Temporal trends and metric variation in the mandibles and dentition of Australopithecus afarensis. J Hum Evol 39:23-55.

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.

A recent spate of articles has carried on a debate about the age of the Sterkfontein hominids. Sterkfontein is a complicated site, including several distinct caverns and deposition layers, called members. The dating of these layers is a serious problem because of their complex stratigraphy and the lack of volcanics that could be subjected to radiometric dating. Until recently the only insights into the age of the fossils came from uranium-series dating and paleomagnetic analysis of calcite deposits in the caves.

The Sterkfontein deposits are divided into six members, and hominid have been recovered from Member 5, Member 4, and Member 2. Most of the hominid remains assigned to Australopithecus africanus come from Member 4, which was long thought to date to between 2.8 million and 2.6 million years. Before Member 5 was deposited, there was erosion on the top of Member 4, and the two are separated by an unknown period of time. This deposit is generally thought to be less than 2 million years in age, perhaps extending as recently as 1.4 million years (Kuman and Clarke 2000). In recent years, excavations lower in the deposit, including the Jacovec cavern and the Silberberg grotto, have produced hominid fossils attributable to Member 2. These were initially believed to be around 3.5 million years old.

The most important fossils from Member 2 belong to the specimen StW 573. The foot bones of this skeleton were initially found in a dump of breccia outside the cave (Clarke and Tobias 1995). The origin of the bones was traced to Member 2, and they were matched to the broken end of a tibia still in situ in the Silberberg grotto. The skeleton is now known to be largely complete, including a skull and mandible, forelimb and hindlimb elements, and much else. It appears to be considerably more complete than the "Lucy" skeleton from Hadar, AL 288-1, or any other australopithecine, but it is not yet fully excavated from the overlying breccia and flowstone. The idea that this skeleton might date to 3.5 million years was potentially very important. At this date, it would be a contemporary of A. afarensis from Laetoli and Maka (it would be earlier than the Hadar deposits). It is not clear yet whether StW 573 anatomically resembles A. afarensis or is more similar to later South African hominids, but this would certainly be an important question to answer from the respect of early hominid phylogeny.

Making Sterkfontein later

McKee (1996) suggested that Member 2 was likely immediately earlier than Member 4. His argument was that the fauna of Member 2 were all found in Member 4, but several species were absent from Makapansgat Member 3 and 4, which date to between 3.2 and 2.9 million years. He proposed that this could be explained by the chance lack of these species at Makapansgat, but viewed that possibility as less likely than the hypothesis that the species appeared after Makapansgat Member 4, to be found in the later Sterkfontein deposits.

Clarke and Tobias (1996) responded to this argument by noting the long stratigraphy of Member 3 between the Member 2 and 4 sequences, with several flowstones that must have taken a long time to deposit. They note that although Makapansgat does not preserve all the Member 2 fauna, the species that are absent are known from other African sites prior to 3.5 million years, and therefore are not of use in dating the deposits. The exception is one baboon species, Papio izodi, which is known only from Member 4 and Taung, and may therefore be rare enough to be absent from other sites.

Berger and colleagues (2002) argued that the entire Sterkfontein sequence is substantially later than had previously been thought. They base their argument on biostratigraphic and paleomagnetic considerations. They have a number of reasons for this:

1. The presence of Equus in the deposit, which is not radiometrically dated in Africa earlier than 2.36 million years ago.
2. In addition to Equus, several other taxa are found in Member 4 that do not have secure radiometric dates above 2.5 million years anywhere in Africa.
3. A later date for Member 4 would suggest that the sequence of magnetic samples from the site should be displaced earlier by a reversal cycle. This would place the top of Member 2 within the Olduvai subchron, and the StW 573 hominid would then date to between 2.15 and 3.04 million years ago. If this is displaced by another cycle more recently, StW 573 would date to as recently as 1.07 to 1.95 million years.

As far as Equus, Kuman and Clarke (2000) are at pains to show that it actually may not occur in Member 4. According to them, only one equine tooth has been excavated from Member 4 in situ, with the remaining bones taken from fill that may derive from Member 5. They argue that the one tooth is insufficient evidence of the presence of the genus, considering the possibility of erosion from later deposits.

Making Sterkfontein earlier

Partridge and colleagues (2003) dated the Sterkfontein Member 2 deposits by using the radioactive decay of cosmogenic isotopes. These are created when cosmic rays from outer space interact with the elements in quartz grains near the earth's surface. In particular, aluminum-26 and beryllium-10 accumulate in quartz grains at a predictable ratio. These two isotopes have different half-lifes (²⁶Al = 1.02 million years, ¹⁰Be = 1.93 million years), which means that once the quartz grain is buried and no longer exposed to cosmic rays, the ratio of the two isotopes changes.

Sediments near the StW 573 specimen gave a date estimate of 4.17 million years, while the orange breccia in the Jacovec Cavern gave an estimate of around 4.02 million years. These date estimates are substantially earlier than were previously estimated for these localities at the site.

It was not possible to date Member 4 in this way, because it is shallow enough that cosmic rays can still affect the quartz grains used for dating.

Partridge et al. (2003) do not present a response to Berger et al. (2002), except to note that their earlier dating "is unsustainable on stratigraphic and faunal as well as on paleomagnetic grounds" (612, note 12). In any event, there seems to be no strong biostratigraphic reason to place Member 2 at either an earlier or later date; the preserved fauna is not specific as to age.

Member 5 stratigraphy

Kuman and Clarke (2000) review the stratigraphy of Member 5. The most important hominid specimen that has been attributed to Member 5 is StW 53, a nearly complete skull that has been variably attributed to A. africanus or Homo habilis. Kuman and Clarke (2000) show that the skull derives from an area that likely is intermediate in age between Members 4 and 5 proper. They call this area the "StW 53 Infill." No artifacts derive from this area. The authors argue that the infill is likely more recent than Member 4 because of the presence in the deposit of Theropithecus oswaldi, a species found in the later Swartkrans Members 1--3, and associated with drier open grassland habitats. On this basis, they place the StW 53 Infill between 2 million years ago and 2.4 million years, which marks the earliest appearance of T. oswaldi in East Africa.

According to Kuman and Clarke (2000), Member 5 can be divided by the presence of two distinct tool industries. The Oldowan Infill dates to between around 2 million and 1.7 million years ago, and preserves 3245 excavated artifacts (Field 1999). The paleoenvironment seems to indicate a grassland. The later phase is referred to the Acheulean because of the presence of bifaces, and is placed between 1.7 and 1.4 million years ago. Like the earlier Oldowan infill, the Acheulean infill represents a predominantly grassland fauna, similar to Swartkrans.

Kuman and Clarke (2000) provide a list of hominid fossils with their probable associations in the stratigraphy. They also discuss the taxonomy of the fossils and their resemblances with elements of the earlier Member 4 and Swartkrans remains.

More on Sterkfontein

More on Makapansgat

References:

Berger LR, Lacruz R, de Ruiter DJ. 2002. Brief communication: Revised age estimates of Australopithecus-bearing deposits at Sterkfontein, South Africa. Am J Phys Anthropol 119:192-197.

Clarke RJ, Tobias PV. 1995. Sterkfontein Member 2 foot bones of the oldest South African hominid. Science 269:521-524.

Clarke RJ, Tobias PV. 1996. Faunal evidence and Sterkfontein Member 2 foot bones of early hominid. Science 271:1301-1302.

Field AS. 1999. An analytic and comparative study of the Earlier Stone Age archaeology of the Sterkfontein Valley. MasterÕs thesis, University of the Witswatersrand.

Kuman K, Clarke RJ. 2000. Stratigraphy, artefact industries and hominid associations for Sterkfontein Member 5. J Hum Evol 38:827-847.

McKee JK. 1996. Faunal evidence and Sterkfontein Member 2 foot bones of early hominid. Science 271:1301.

Partridge TC, Granger DE, Caffee MW, Clarke RJ. 2003. Lower Pliocene hominid remains from Sterkfontein. Science 300:607-612.