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Thursday, April 07, 2005

Lean on Dmanisi

Originally written for noodly.org, but archived here on account of flux and wanting to refer to it.

First, I should reveal that y'all are likely better off reading Pat Shipman's excellent article Doubting Dmanisi than this. That's not going to stop me from blathering on for a good long while, mind you, but I love, therefore I disclose.

The third article in yesterday's Nature that got the scientific blood a-pumping was a nicely written, unassuming piece. The straightforward reporting and elegance of the conclusions are also typical of the two previous publications in Science regarding the same site, and of the original 1993 Nature paper. This scientific cool is all the more impressive given the massive potential of the finds for shaking things up as well as the fact that the team has been waiting for 12 years for real acceptance of their work. All in all, this is a most refreshing contrast to the kind of shennanigans evident in the Sahelanthropus saga (and, let's face it, most of paleoanthropology). The newest paper is the icing on a painstakingly constructed cake. This is a cake that required a substantial labor force in the strawberry mines. As ever, a bit of background is needed.

Part of the problem with paleoanthropology is that discoveries have proceeded ass backwards. The earliest hominid finds were Neanderthal and Cro-Magnon individuals in Europe, followed hot on the heels by things in the Far East that we then called by catchy titles like Homo pekingensis and Homo modjokertensis (no, really, I only wish I'd made that up) and that we now call by the wholly misleading Homo erectus. It means "Upright Walking Man," which, ok, true enough. He is upright walking, it's just that his daddy, grandaddy, and probably great-grandaddy are too. it's just kind of like calling "A New Hope" Star Wars. Oh . . . ahem. Moving on.

The earliest finds reinforced the already fairly robust tendency to emphasize Europe and Asia in all things. So, despite the hunch by Darwin that Africa would figure prominently in hominid evolution, no one felt too much like ferreting out relatives on the Dark Continent. As an aside, that attitude survives as evidenced by the coverage of the find of Pierolapithecus catalunicus, a 13 myo ape, in Spain earlier this year. The popular press was most relieved to reassure us that Europe had been restored to its status as the Cradle of Humanity (no mention of it also being the cradle of chimpanzee-ity, bonobo-ity, gorilla-ity, and orangutan-ity, as well).

Once Africa was established quite definitely as the place we ought to be looking if we wanted the good parts version of the human story (a good 25 years after a certain child's skull miraculously escaped getting blowed up real good and found its way to one Raymond Dart), there was trouble connecting the dots. Who, when, how, and why the first hominids left Africa and populated the rest of the world became the $64,000 question.

Delving into these matters was complicated by worsening political relationships with the Far East. Oh yeah, and we lost the Peking Man fossils. And by "we," I mean the US Marines. What little information we could elicit regarding relative dates and so on led paleoanthropologists to put hominids in Southeast Asia by about 1 mya. Material from Africa fit in well with this timing as specimens assigned to Homo erectus began to emerge from the African record in strata dating to about 1.8 mya.

Paleoanthropologists have the mentality of yuppie parents. Our kidlets need to be doing everything NOW or at least before those trailer trash brats from the next tuft over do. Well you're standing up, aren't you? Why don't you have a flipping huge brain? You see those giant rock outcroppings? They're chock full o' tool-making goodness. If you'd just exert yourself a bit, you could be the mightiest predator on the savanna! To a mindset like this, there's no excuse for lying about in Africa for 800,000 years when Asia beckons.

There must have been a technological whizzbang that allowed them to get outta Dodge, and the gadget commonly favored was the Acheulean hand axe. Homo erectus is associated with two tool industries: The Developed Oldowan Industry (a variation on the "Hey, I love to bash things. If I bash THIS rock with THIS rock, I have a SHARP rock and I can Bash and Slash!" original stone technology), and the Acheulean industry, which involves more specialized tool forms and more extensive modification to make them do their jobs better. Once humanity figured out how to turn over the piece of rock and work on the other side, so the story goes, they were hell-bent for leather.

On the flipside, the aging-hippie-parent paleoanthropologist argues, Indonesia's a hell of a jaunt. No rush. It's not like the Dead are playing or something. In this corner, paleoanthropologists eyed up the hand axe and said, "It's a rock. I can't wait to tell my friends. None of them has a cutting edge so efficient for the same amount of stone by weight." The idea of hominids scraping their way out of Africa was not, to say the least, a compelling tale. This camp favored a multifactorial ecological model, whereby hominids accumulated behavioral changes gradually that eased them Northward and thence East.

In addition to the temporal issue, there's an irritating lack of geographical continuity in fossil finds during this period, making the timeline and pace of the first migration out even more difficult to construct. And then in 1993, Dmanisi first reared what would prove to be a breathtakingly tiny, sagitally-keeled, yet undeniably hominid head.

The site is in the Republic of Georgia "at the gates of Europe" as many have become more recently fond of pointing out. "Humanity was in Europe---or at least the gates of it---nearly two million years ago," they'd say, working hard not add "Boo ya! In your FACE Africa!"

The first hominid-relevant fossil from Dmanisi was a mandible (lower jaw, with teeth) the authors believed to be near 1.8 myo. Despite the minimal nature of this find, the jaw's relative completeness and minimal damage allowed for extensive comparisons with other hominids. Gabunia and Vekua believed it was Homo erectus. They believed that the evidence so clearly spoke for itself that they brought the original fossils to the conference at which they unveiled it, casually granting unlimited access to colleagues (although this is not unheard of, it's rare; it's also risky as the heart-breaking story of the Homo floresiensis fossils makes clear). Pat Shipman and Alan Walker, perhaps the two most qualified to assess the jaw, were convinced. Milford Wolpoff started a knock-down, drag-out fight about whether Homo erectus existed at all, and almost everyone forgot about Dmanisi.

In 2000 and again in 2002 Dmanisi didn't so much burst on to the scene as it quietly left a really kick-ass cake on the front porch with a polite note. They had skulls with clear morpohological affinity to the African variant of Homo erectus (often called Homo ergaster in an attempt not to squander our precious multisyllabic Latin resources), with a few important twists. The 2002 skull, in particular, was tiny, holding a brain that was estimated to be 600 cc. Assuming that you all don't spend your Friday nights lining up the skulls in your house in order of cranial capacity (which we at the Painful Acres totally don't), let me give you an idea of what that means.

The Australopithecines have brains that are about 400 cc by volume, more or less in the range of modern chimpanzees. When Louis Leakey claimed that the earliest members of genus Homo (a species he called H. habilis, the first toolmaker) had brains that were about 650 cc, there was tremendous resistance. After all, Sir Arthur Keith had closed his countryclub to any creature whose brain wasn't on the right side of the Cerebral Rubicon (750 cc), and this Bill Frist of his time went to his grave believing in Piltdown Man. We should totally take his word for it.

Paleoanthropologists have remained somewhat uncomfortable with the subtlety of the brain expansion from the Australopithcines to Homo habilis. In fact, there's still a substantial movement in the field to do away with the designation altogether, lumping most of Leakey's specimens into genus Australopithecus (don't ask them about the very modern-looking hands and feet; they get cranky). With the brain of Homo erectus ranging all the way up to 1100 cc, though, everyone breathed a sigh of relief. Now, we're talkin' encephalization! The Dmanisi hominids ever-so-gently warned the scientific community, once again, against placing too much emphasis on brain volume as the one and only proxy for intelligence and behavioral advancement.

In addition to the skulls, Dmanisi yielded thousands of stone tools and high concentrations of animal bones bearing cutmarks from them. This was potentially balm for the yuppie parents' souls. We've always been in a big rush to get to the meat-eating part of the story. So these little-brained things have some superfancy tools, and then the start beating the crap out of things and running around with blood dripping from their maws, right? RIGHT? Well, not so much with the fancy dancy tools. The lithics from Dmanisi are quite stubbornly Oldowan I. This news is brown slacks from Sears for Christmas. It is a little brother in lieu of a Snoopy Snow Cone machine. It is Lee Carvallo's Putting Challenge instead of Bonestorm.

The Dmanisi message, as it unfolded, was stunning. Hominids left Africa much earlier than previously expected, and they did so with minimally expanded brains and incredibly rudimentary tools. The 2002 article suggested that we would even have to consider the possibility that Homo erectus (sensu lato) was not the first to make it out of the natal household, but rather something at least more basal if not flat out belonging to Homo habilis.

And still the question remained, "How did they do it?" What finally enabled and or compelled them to move into environments for which their tropical body type was ill-suited? What adaptations made the difference in allowing them to thrive in temperate, seasonal climates with that body type?

Leaving aside the question of how they got animal protein for a moment (those simple tools are still sticking in our collective craw), there's good evidence that exploitation of animal protein was a key adaptive strategy. All previous hominids are primarily vegetarian and only got the hint about exploiting animal resources about 2.5 mya. In a seasonal environment, animals represent calories stored on the hoof/paw/thumpy widdle bunny leg, etc. The sheer number of animal bones bearing tool marks at Dmanisi make it clear that hominids are hunting for the first time.

But if we've learned anything over the last century and change of paleoanthropology (and many of us have not), it's to give unifactorial explanations the hairy eyeball. But the additional factor currently stepping up to the plate is one that's fairly unexpected.

There's a brand new skull from Dmanisi this week. Morphologically there's not a lot new. Its brow ridge is in line with what we expect. The cresting on the back of the head where the neck muscles attach is not particularly exciting. Endocranial capacity is middling. And, oh yeah, it hasn't got a single tooth left in its head. This individual had lost all his teeth years and years ago and the tooth sockets had been completely resorbed, the mandible shrinking to less than 1/3 its original height.

Unlike the current state of affairs, the teeth of Homo erectus would most definitely have been considered to be part of the body. We often casually note that our teeth become pretty much irrelevant as tool technology develops. I suppose that's true if your head has a hinge and you can pop all your food directly down your gullet. This individual does not have a hinge in his head. He survived for years, either unable to chew his own food at all or having to lobby extensively for the squishy bits.

There's a strong chance that this individual survived with the help of his social group. Adult individuals cooperating economically is a rare thing in the animal world to begin with. Biologically, we define altruism as sacrificing a portion of one's own reproductive fitness to benefit someone else. Arguably, humans have a highly elaborated form of altruism that ensures the survival of those who are "less fit" due to age, infirmity, or simple ineptitude when it comes to not starving, not getting eaten, not falling off a cliff, etc. For this last, yours truly is sincerely grateful.

The earliest altruistic behavior in hominids has traditionally been attributed to Neanderthals, a form of hominid very much like anatomically modern Homo sapiens, if not outright belonging to our very species. The capacity to envision value in caring for individuals who can't contribute economically in the usual ways marks a substantial cognitive shift. It's often used to argue for Neanderthal capacity for symbolism and, therefore, for language. The idea that the small-brained, technologically simple hominids at Dmanisi could have had the first inklings of this capacity nearly 1.7 my earlier than anyone had imagined is staggering.

So what do our level-headed authors have to say about this? Surely at this point, they're allowing themselves a well-earned, slightly smug SQUEEEEE! Not so much. The paper includes one extremely sly nod to the entire issue of altruism:

"The subsequent mid-Pleistocene Bau de l'Aub├ęsier and La Chapelle-aux-Saints specimens had a more intact dentition at the time of death."

That's Chow Yun Fat levels of cool right there.

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