Dental Work

I probably shouldn’t tell you this, but every time I read or type the abbreviation, “B.C.” I flash on The Flintstones. Also John Hart’s comic strip, although that one may be generational.

This month we embrace the old, the Seriously Old, and the Ridiculously Old as told in Our Human Story by Louise Humphrey and Chris Stringer. There are several things to be aware of with this volume. Despite its dreadfully inclusive title, it is an actual work of science, one that considers the evolution and emergence of humans…yes, we are reading anthropology, don’t tell anybody. The volume spans the period from about seven million years ago to the general distribution of Homo sapiens (that would be us) across the world in the modern era. This book is also pitched to a popular audience, meaning it is written more nearly at the high school level than college or beyond. Perfect for our purposes…the Curmudgeon confesses a limited interest in fossil teeth, and more importantly, we are reading this month with a Hidden Agenda. More on that in a bit.

Ironically, while anthropology considers the oldest of human experience, it is one of the newest scientific disciplines. Many of the most relevant fossil discoveries did not take place until the early twentieth century and are continuing today. Moreover, it’s worth remembering that we needed both Darwin (On the Origin of Species, 1859) and Mendel (Experiments on Plant Hybridization, 1866) to make sense of the fossil record. That nineteenth century basic science, coupled with key excavations in the early twentieth century, set our understanding of human evolution. The research has been furthered by DNA analysis in recent decades…and yes, you can get DNA out of an old, fossilized skeleton.

Let us begin by ticking off some of our more famous ancestors.

Modern day humans got our first big break when the predecessors of humans (the “hominins”) separated from the chimpanzees. The hominin side of that divide brings us to Sahelanthropus tchadensis (“Saharan hominin from Chad”), your ancestor and mine, who lived just about seven million years ago, at the time of the split. In him we see the divergence from chimps: notably, reduced canine teeth and corresponding lack of a gap in the dentation; and the hole where the spinal cord enters the cranium, the foramen magnum, has moved forward, indicating upright walking. S. tchadensis represents the oldest genus of three that comprise the Early Hominins (the others were Orrorin and Ardipithecus), who exhibit one or more characteristics of modern humans. The fossils that exist are incomplete, meaning we don’t have a full skeleton of any individual and we have different skeletal fragments for each of the three genera, so their relationship is imperfectly understood.

As you might expect, the party picks up considerably with the arrival of the Australopiths.

The genus Australopithecus appeared about 4.2 million years ago. The Australopiths are well represented in the fossil record, with a half-dozen or so known species, and they lasted until about 2 million years ago. They walked upright, but retained some adaptations to climbing; and significantly, their hands had evolved for fine motor control of objects, including tools. They also overlapped with other hominins…the Australopiths coexisted with Ardipithecus in their early days, and with a later genus, Paranthropus (which means “alongside humans”), starting about 2.6 million years ago.

Finally, just under two million years ago the Homos arrive. Fashionably late, of course.

The genus Homo — that would be you and me, Homo sapiens in our case — arrives in the person of Homo habilis, “Handy Man,” who appeared about 1.9 million years ago. He is distinguished from the Australopiths by his smaller, more human-like teeth (again with the teeth) and his relatively larger skull size, brain volume, and thinness of the skull. Perhaps the most successful of our early Homo ancestors was Homo erectus. He appears shortly after H. habilis, somewhere between 1.5 and 2 million years ago; and he was the longest-lived Homo species, surviving for about 1.5 million years…meaning quite close to our own time.

H. erectus also seems to have been the species that first spread beyond its origins in Africa, throughout the world. The current belief is that shortly after he emerged in Africa, H. erectus spread to western Asia (fossils are found in the country of Georgia, and we have run across them in our consideration of early India), then to eastern Asia (there are finds in China), and into southeast Asia as far as Java. The evolution of H. erectus did not stop when he left Africa, of course, and skeletons show significant variation in things like length of legbones; some thought is given to the idea that these variations evolved to aid in hunting in different environments.

While H. erectus was off conquering Eurasia, our own species, H. sapiens, was busy evolving back in Africa. The earliest H. sapiens fossils date from at least 260,000 years ago (South Africa) to possibly 320,000 years ago (Morocco). By about 160,000-195,000 years ago we find remains in which the skeletons fully express modern human anatomy. Today we are the only Homos left, but for much of time we co-existed with other members of our genus. As we’ve seen, H. erectus overlapped us. The Neanderthals — scientifically speaking, Homo neanderthalensis — not only co-existed with us (they became extinct only 39,000 years ago), they are close enough to us genetically that we search for the last ancestor we have in common with them. A topic of some debate, that ancestor is provisionally called H. antecessor and the split may have occurred at either 500,000 or 850,000 years ago, depending on which side of the debate you believe. There is genetic evidence of some low level of interbreeding between modern humans and Neanderthals after the split, which may help explain some of the bosses we’ve all had over the years. While cross-species sex represents only background genetic noise, it was real and contributed to our own evolution.

Put another way: mate-swapping is as old as humanity. Or older, depending on who else the Neanderthals were zooming.

Earlier we teased a Hidden Agenda in reading Our Human Story, and here it is. Like me and the Flintstones, we’re all sloppy in using terms for things that are old: “That’s prehistoric!” really only takes you back to about 3000 B.C. or so, to the origin of the written record. “Before civilization itself!” is a notch better, but only gets us back to 7500 B.C. and the first cities…before that we were tribal and often nomadic. At every stop, we find human behavior looks amazingly familiar, with all its greed and generosity, sex and compassion intact. So our question, our Hidden Agenda: just when did human nature enter the picture? Unfortunately, it is not a topic of interest to our authors, but they do give us a few clues. They themselves discuss the difficulty of inferring cognition from anatomy. However, as a marker they point to the cave paintings at Lascaux. Dating to about 35,000 years ago, these artworks demonstrate the ability not just to document human experience (in this case, a hunting expedition), but to interpret and abstract it. Clearly by this point, most if not all the features of the human mind had evolved. It isn’t a solid proof, but we can take as a good hunch that all the delightfully bad social behavior that historians read and write about had begun by at least 35,000 years ago.

The real question is why of all these Homo species, we are the only ones left surviving. And the real answer is that we don’t know why. Traditionally we flatter ourselves that H. sapiens was just such a great competitor that we drove everybody else out of business. Our authors temper that a bit and point out that some of the other species may have been small populations, already at risk of extinction. It remains a serious question, and one that scientists continue to research.

However, from a conceptual/literary/science fiction standpoint it’s golden: modern humans evolved, we took over the world, and we completely exterminated our predecessors. Then we destroyed all knowledge of how we did it.

And you thought The Matrix had a sinister plot line.