Olduvai Gorge

I've had on my stack for quite a long time, a short paper by Nicholas van der Merwe and colleagues, assessing the stable carbon isotope ratios in several specimens from Tanzania. These include the Homo habilis specimens OH7, OH62 and OH65, and the A. boisei specimens OH5 and the Peninj mandible.

The ratio of stable carbon-13 and carbon-12 enable an assessment of the amount of C₄ versus C₃ plants in the diet. I discussed the basic ideas in a longer post from 2005.

The results on the Homo specimens are not too surprising. All three specimens overlap with South African A. africanus. OH7 and OH62 in particular have values around 20% C₄, which is right near the mean observed for South African Homo and A. robustus from Swartkrans. OH65 has a higher C₄ percentage than the other two, but within the range observed for Sterkfontein Member 4 A. africanus, which was significantly higher than Makapansgat or the other South African samples. So it would appear that the diet of Homo habilis did not differ from earlier hominins in terms of the ultimate origin of carbon in grasses versus non-grass plants.

What is more surprising is the extremely high amount of C₄-derived carbon in OH5 and Peninj. They score 77% and 81% C₄, respectively. These are the only two specimens of A. boisei for which these stable isotopes are known, and they are very far from the observed range in the South African A. robustus.

The authors suggest an interesting source for this high C₄ proportion -- papyrus. They described a tasting tour of the wild plants of the Okavango:

Bamford and van der Merwe investigated (and ate) the edible plants of the Okavango Delta in Botswana during the dry season (July 2003), assisted by Ezaya Karesaza, a tourist guide who grew up in this extensive wetland. Among the C₃ plants that are traditionally eaten raw in this region are a variety of fruits and seeds, as well as plants of which the leaves and rhizomes are eaten. The latter include Aeschynomene fluitans, a floating legumi- nous plant, of which the leaves taste like lettuce; Typha capensis, which grows in thick stands along the water’s edge, of which the rhizomes have a pleasant taste; and Schoenoplectus corymbosus, a big water sedge, of which the stem is succulent at the bottom end. Among C₄ plants, the rhizomes and culms of three other species of sedges are edible. These include Cyperus denudatus and C. dives, which grow in the grasslands of the floodplains. Unlike the grasses, they are green year-round, although not particularly prolific. The most common C₄ sedge, by far, is Cyperus papyrus, which grows in dense thickets along the water edge. This species has culms as high as 4 m, of which the lowermost 0.5 m is frequently chewed by local people. It has a soft, white rind about 0.5 cm thick; the interior, about 2 to 3 cm in diameter, is more fibrous. It is chewy and pleasant tasting. The thick rhizome of papyrus is more fibrous and starchy than the culm, somewhat astringent, and requires considerable chewing effort. It produces a bolus in the mouth that has to be spat out at intervals.

They then reported the results of a nutritional analysis of the papyrus culm and rhizome, which have roughly the nutritional and caloric value of domestic potatos, although would require a significant gut flora to deal with the cellulosic content.

All in all, it's very curious that A. boisei is so different in these isotopic values compared to other early hominins. The theme was picked up last year in a paper by Richard Wrangham and colleagues, who focused on the idea of "fallback foods" -- the kinds of foods that an animal does not prefer, but eats when other more highly preferred foods are not available. Considering the very high C₄ proportion indicated by the OH5 and Natron isotope values, it doesn't seem likely that this reflects a fallback strategy, but possibly an initial exploitation of such resources as fallbacks facilitated a later, more developed adaptation to them.

Related posts:

"Chemistry and early hominid diets"

"Robust australopithecine diet ablated"

"Average diet versus extreme diet in robust australopithecines"

References:

van der Merwe NJ, Masao FT, Bamford MK. 2008. Isotopic evidence for contrasting diets of early hominins Homo habilis and Australopithecus boisei of Tanzania. S Afr J Sci 104:153-155.

Wrangham R, Cheney D, Seyfarth R, Sarmiento E. 2009. Shallow-water habitats as sources of fallback foods for hominins. Am J Phys Anthropol 140:630-642. doi:10.1002/ajpa.21122

I want to share a paper that might not get a lot of attention but that I think makes an interesting contribution to understanding the ecology of early Homo after its initial dispersal from Africa. The paper is by José Joordens and colleagues, in the early bin at Journal of Human Evolution, titled, "Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia)".

The authors plowed through the old collections of fossil fauna from Trinil, originally from Dubois' excavation, looking to characterize the paleoenvironment in terms of hominin habitat preferences. The fauna are Early Pleistocene in age, possibly as old as 1.5 million years ago, but some uncertainty surrounds that date assessment, which is possibly under a million. What they found was some strong hints that the Trinil humans may have been eating shellfish and using other resources from the swampy lowlands in which the site was formed.

If aquatic resources such as molluscs and fish were available for hominins on Java, what is the probability that they indeed consumed these resources? In coastal areas, terrestrial predators often consume aquatic foods and have a considerable impact on the local aquatic ecosystem (Polis and Hurd, 1996; Roth, 2003). Systematic, often seasonal, predation by non-human terrestrial mammals on freshwater and marine fauna occurs widely. Carlton and Hodder (2003) reviewed occurrence of terrestrial mammals as predators in marine intertidal communities and documented 121 records of intertidal predation among 38 species of terrestrial mammals. For instance, mice, rats, pigs, chacma baboons, brown bears, black bears, striped and spotted hyenas, coyotes, domestic dogs, grey and red wolves, jackals, and foxes in coastal habitats catch and consume crabs, molluscs, fish, and other aquatic fauna (Carlton and Hodder, 2003; Smith and Partridge, 2004).

Terrestrial predators and omnivores eat fish, crabs, crayfish, turtles and shellfish when they get the chance. But the long list here muddies the water, so to speak. We often find hominins in lacustrine and riverine contexts, both because they inhabited those places and because of preservation biases. Those environments often yield evidence of consumption of aquatic organisms, especially shellfish but also fish, crocodiles and aquatic mammals. Somebody ate those animals, and the list above gives a bunch of suspects that aren't hominins.

So maybe we should redirect our null hypothesis -- instead of demanding proof of every instance of Early Pleistocene exploitation of aquatic foods, we should assume they ate the foods available to them. But with 30 or more species noshing on clams, crabs or fish at the shoreline, it's going to be tough to diagnose cases where humans may have been involved.

Well, anyway, what would this reorientation mean for our understanding of the behavioral breadth of early Homo?

The literature cited above shows that systematic aquatic exploitation (either year-round or seasonal) by terrestrial mammals is normal and predictable mammalian behavior when the mammal is 1) omnivorous, 2) living in a coastal marine or freshwater habitat, 3) where nutritious and catchable aquatic prey is available. Considered in the perspective of aquatic exploitation by terrestrial mammals in coastal habitats, the systematic and seasonal aquatic exploitation by Homo sapiens (Marean et al., 2007) and H. neanderthalensis (Stringer et al., 2008) does not differ from that of other mammals. Also, transport of aquatic prey to a base (such as a cave, in the case of H. sapiens and H. neanderthalensis) is not ‘‘modern’’ behavior. For example, Navarrete and Castilla (1993) reported that Norway rat burrows in coastal Chile contain remains of w40 intertidal prey species such as limpets, bivalve molluscs, crabs, and fish. Erlandson and Moss (2001) provide many more examples of terrestrial omnivorous animals transporting aquatic food (remains) to dens, nests, burrows, and caves on land. A label of ‘‘modernity,’’ if applicable at all to aquatic exploitation, should perhaps be reserved for aquatic exploitation with evidence of advanced technology such as fish hooks and boats. The assumption, that early hominins living in a coastal habitat with catchable nutritious aquatic fauna were restricted to eating terrestrial resources, does not agree with published accounts of common mammalian behavior. Therefore, instead of having to provide evidence of aquatic exploitation before it is considered as a realistic option, we propose that the default assumption in hominin evolutionary research should be that omnivorous hominins who lived in coastal habitats with catchable aquatic fauna could have consumed aquatic resources (Joordens et al. 2009).

I like this point a lot: It is a bad sign when archaeologists use a definition of behavioral modernity includes rats but not Neandertals.

Joordens and colleagues suggest that the Trinil faunal collections may already contain evidence of waste heaps (they say, "midden-like" accumulations) of shells:

[T]he presence of a relatively large number of only adult, large-size Pseudodon shells, excavated from a very limited area (Hauptknochenschicht in Trinil), in both the Dubois and Bandung collections, is a discrepancy in the aquatic assemblage that merits further attention for these shells.

But there aren't literally heaps of shells in the records; they have the shells and can only infer their original locations within the excavation at a relatively course grain. So the persuasive parts of the assemblage require us to see through the differnet biases that might have affected the collection. After dismissing a number of possible objections, they continue:

The fact that many of the Pseudodon valves are still paired and well-preserved would suggest that the molluscs were not dead and transported by water before fossilization but were buried in live position. However, the complete absence of small, juvenile shells as well as the mixed occurrence of two different (but equally large-sized) shell forms argues against interpretation of burial of a live population (Van Benthem Jutting, 1937). Instead, the discrepancies suggest that the Pseudodon shells could have been brought together, prior to fossilization, by a size-selective collecting agent who may have used them for consumption of molluscan flesh (Joordens et al. 2009: 13).

They found a similar pattern for another species:

The Elongaria assemblage from Trinil, just like Pseudodon, appears to indicate collection by a selective agent for the purpose of mollusc consumption. The Pseudodon and Elongaria assemblages from Trinil have the characteristics of shell middens (e.g., Waselkov, 1987; Rosendahl et al., 2007): large adult shells only, many complete shells, no signs of damage due to water rolling, signs of damage due to being deliberately opened, presence of human (hominin) bones in the same layer. We conclude that they represent a subtle clue of possible aquatic predation by non-hominins or by hominins (ibid.).

This hypothesis may not be testable further, unless signs of deliberate modification are found on one or more shells. Joordens and colleagues write that such a study is "currently underway". The only other thing to do is apply a higher standard of rigor to possible shellfish features in other Early Pleistocene contexts. Early Pleistocene surface collections dug by vertebrate paleontologists (as opposed to archaeologists) sometimes discard or leave fish bones unidentified, and it is not always clear whether a loose association of shells would be recognized as a possible hominin-accumulated feature.

The paper cites the work of Stewart (1994), who argued for fish consumption at Olduvai Gorge. From that abstract:

Fish remains are associated with many early hominid sites, and five sites at Olduvai Gorge are examined here in detail. The patterns of fish exploitation seen in Late Pleistocene archaeological sites are manifested in three of the Olduvai Gorge sites, making a strong, although not absolute, case for early hominid fish procurement. The implications for early hominid behaviour of fish procurement are several, and include timing of the early hominid seasonal round to exploit spawning or stranded fish, and group size larger than the nuclear family unit, with greater social interaction.

These examples bring to mind the challenge of identifying chimpanzee nutcracking archaeologically. The chimpanzee pattern of behavior is barely systematic enough to pick out from the background. Yet archaeologists have devised some ways to find that slim signal, at least in contexts where they expect chimpanzees to have been active. Late in prehistory, some shell middens were vast and highly-recognizable. Those populations put together the elements of recurrent (or constant) occupation of a site and recurrent transport of shellfish to that site for processing. When we look further into the past, even Neandertals rarely put together those elements in a recognizable way. At the Italian sites where Mary Stiner showed Mousterian shellfish consumption, the presence of shellfish is just at a level where the signal can be picked out due to the lack of other credible transport agents for shellfish remains.

A hitch: Suppose we accept that early humans commonly exploited aquatic resources, even in the absence of specialized archaeological traces of such dietary sources. That does seem to create a problem for the interpretation of stable isotope ratios in fossil humans. I wrote about this issue regarding Neandertal diet ("Neandertals: gone fishin' or not?", see also "Shellfish use by Neandertals" and "Neandertal diet was not dolphin-safe"). It doesn't take much fish to increase the nitrogen-15 composition of bone, making it hard to test hypotheses about the proportion of different terrestrial prey species, and even behavioral interpretations such as weaning age may be thrown off. The problem is too many independent dietary parameters to test with only one estimate. Ignoring the possibility of aquatic resource use helps simplify the interpretation, but that doesn't necessarily make it better.

References:

Joordens JCA, Wesselingh FP, de Vos J, Vonhof HB, Kroon D. 2009. Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia). J Hum Evol (in press) doi:10.1016/j.jhevol.2009.06.003

Stewart KM. 1994. Early hominid utilisation of fish resources and implications for seasonality and behaviour. J Hum Evol 27:229–245.

In the current AJPA, Randall Susman reviews the stratigraphic and morphological evidence concerning Olduvai Hominids 7, 8 and 35. Some history:

Fossil evidence of Homo habilis was recovered from Olduvai in 1960–1961 (Leakey, 1960, 1961a,b). When first reported, a hand, foot, and clavicle, from site FLK NN Level 3, and a leg from FLK ‘‘Zinj’’ (Level 22) represented the first early hominid postcrania recovered in East Africa. Together with a mandible and fragmentary skull the fossils from FLK NN Level 3 were reported to be those of a single juvenile whose age at death was [ca.] 12 years (Leakey, 1961b).1 After the initial reports, Day and Napier (1964) concluded that while the jaw, skull, and and were those of a ‘‘child,’’ the foot represented an adult and thus signaled the presence at FLK NN 3 of a second individual. Day and Napier ’s conclusion was based on the presence of what they considered to be ‘‘age-related’’ arthritis in the midfoot and metatarsus (M.H. Day, personal communication). The mandible, skull bones, and hand, were designated OH 7. These fossils became the holotype of the new species, Homo habilis (Leakey et al., 1964). The foot was catalogued as OH 8, and placed in the paratype along with other craniodental and postcranial fossils by Leakey et al. (1964). In their diagnosis and description, Leakey, Tobias and Napier maintained that the holotype, OH 7, was a subadult while other postcranial remains, including OH 8, OH 35 (a leg), and OH 48 (a clavicle), were the bones of adults (Susman 2008:356).

In the paper, Susman argues that OH 7 and OH 8 probably represent a single adolescent individual. His case depends on two points: (1) OH 8 is a subadult of equivalent age to OH 7, contrary to the earlier conclusion which suggested that OH 8 is an adult; and (2) it is "much more likely that OH 7 and OH 8 represent the same subadult individual than they do twin adolescents who died at the same time at FLK NN Level 3 and left complementary body parts (360)."

This review depends extensively on Susman and Stern's (1982) article, "Functional morphology of Homo habilis", but adds some new detail to the age assessment. The case that OH 8 is subadult is reasonable, and on that basis it is also reasonable to attribute the OH 7 remains to the same individual. Thus, the OH 8 foot would be part of the holotype (defining individual) of Homo habilis. The conclusion remains debatable, as all issues of attribution are, but it is reasonable.

Additionally, Susman suggests that the OH 8 foot may belong to the same individual as OH 35, an associated tibia and fibula. This is a harder case to make, because OH 8 and OH 35 come from distinct geological strata: OH 8 from FLK NN 3, and OH 35 from FLK "Zinj" (Level 22). Additionally, at least two different analyses of the OH 35 tibia and the OH 8 talus conclude that the two don't match each other at the ankle joint. So, it's an uphill climb.

Susman writes, based on a lithological resemblance of FLK NN and FLK "Zinj", that we might reconsider whether the two necessarily sample different times. Still in the end he concedes that the association is geologically unlikely, and defers to current stratigraphic opinion. This takes the force out of his argument.

Even so, he makes a morphological case why OH 35 and OH 8 would make sense as a single individual. He points out deficiencies in earlier analyses that suggested they are inconsistent at the ankle joint, and claims that both exhibit similar signs of traumatic injury and similar taphonomic signs of carnivore and/or crocodile predation.

I think there's some irony here. If we accept that the resemblances between OH 35 and OH 8 must be accidental -- as the stratigraphy indicates --- then we must conclude that morphological compatibility is at best a weak argument for identity. But Susman's argument for OH 7 and OH 8 essentially boils down to a claim that morphological compatibility demonstrates identity. Whatever we might claim about what "parsimony dictates" (357), the comparison to the OH 35-OH 8 question undercuts the case for an OH 7-OH 8 identity. Even accepting that OH 8 is a subadult, the demonstration that they are of "consistent" relative ages means only that we cannot disprove the null hypothesis that they are the same.

Still, in this case, perhaps that's enough. In particular, the OH 7=OH 8 hypothesis needs to be considered more carefully when we discuss H. habilis limb proportions. This discussion is otherwise dominated by OH 62, which has weaknesses of its own. In the absence of a convincing association of OH 7 with OH 8, others have observed similarities of OH 8 with robust australopithecine tali (notably Kromdraai TM 1517, c.f., Gebo and Schwartz 2006). If OH 8 is associated with OH 7, it argues for a wider view of diversity of talar morphology in early Homo. Since early Homo appears to be morphologically diverse in most other respects, it hardly makes sense to define a fossil talus as Homo or Australopithecus on the basis of similarities to later large-bodied humans.

References:

Susman RL. 2008. Evidence bearing on the status of Homo habilis at Olduvai Gorge. Am J Phys Anthropol 137:356-361. doi:10.1002/ajpa.20896

Susman RL, Stern JT. 1982. Functional morphology of Homo habilis. Science 217:931-934.

Gebo DL, Schwartz GT. 2006. Foot bones from Omo: Implications for hominid evolution. Am J Phys Anthropol 129:499-511.doi:10.1002/ajpa.20320

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.