The big news this season is in the bones
By Tom Baxter
Often the biggest news stays buried longest. This fall we’ve witnessed another government shutdown, the chaotic roll out of the health care networks and the reemergence of polio, long forgotten, in war-torn Syria. But there’s a good chance that in the future, the announcement of what’s been unearthed in that other Georgia on the other side of the globe will be looked on as this season’s biggest development.
For a long time, the people who study these kinds of things thought of human evolution as a family tree. Over the past few decades, as a wide variety of human-like, or hominin, specimens were discovered, that concept was replaced by the idea of a family bush. Many related species evolved over time, researchers concluded. Each new discovery generated a new species name — homo habilis, homo ergaster, and so forth — making the bush progressively thicker. Only one of these species survived — but which? — and evolved into homo sapiens, which is us.
These assumptions have been challenged in a dramatic way by a study published this month in Science magazine. Anthropologists who’ve been working at a site in Dmanisi, in southern Georgia, offer evidence that the older concept of a tree may be closer to the truth.
By 1.8 million years ago, a hominin species had left Africa and found its way to a watering hole which would one day become the Dmanisi site. Scientists have pieced together five skulls of individuals who were killed and dragged into dens to be eaten by the big cats which lived around the same watering hole, over the course of a few hundred years. Nothing like this has been found anywhere else, nothing that puts so many examples of the same species together in such a narrow space of time.
Skull 5, the last of these to be unearthed, is the only fully complete skull ever found from the period when hominins were evolving into what we call humans. Scientists talk about the “beautiful skull,” as it has been called, with an open wonder that is rare in these circles.
Skull 5 is not only a beautiful specimen, it’s a total surprise. Its long face seems much more fully evolved than its brain pan, which is very small. It’s so different from the other skulls, researchers noted, that if they had been found at different locations, they would have been classed as different species.
That caused the anthropologists to reconsider the discoveries of the past few decades, and to take a second look also at the amount of diversity within other ape species. Their conclusion, based on the diversity demonstrated at Dmanisi, is that what were thought to be several species are only variations of the same one. They didn’t separate by region into different species, a la Darwin, but developed a common gene pool over a very wide area, with often dramatic variations within groups. The genetic strands which bind us all together were more loosely bound in the beginning, and nature tinkered with a lot of alternatives before settling on our model. This also means the common ancestor of all homo sapiens was a lot older than had been thought.
So far you are thinking, what does this have to do with anything that’s going on now? Only time will tell. Big ideas in science, like evolution or electrical conduction, have a way of creeping into the wider discourse and affecting the way we think about a lot of things.
Over time, the idea that we spring from a wide, central trunk and not some random shoot may change the way we look at ourselves, just as the realization that the earth circled the sun gave us a different view of our position in the universe. The realization that our keyhole view of a huge past caused us to think that one species was really several could also cause us to look at other things and seek simpler explanations than the ones we have.
Anyone who has followed the many twists since the 1991 discovery of Otzi, the 5,300-year-old mummified ice man, or homo floresiensis, the tiny human relative discovered in Indonesia in 2003, knows that the study which advances this new view of human evolution is probably only the first salvo in what promises to be a very long exchange. The conclusions which have upset the previous consensus may be overturned themselves by future study.
Some skeptics take this willingness to adjust to fresh information as evidence that the whole theory is shaky, that ideas like evolution are, in the memorable words of U.S. Rep. Paul Broun, “lies straight from the pit of Hell.”
In fact, the ability to recognize a mistake and change your mind is one of the great strengths of the scientific method. It’s when we won’t change our minds, regardless of what we learn, that we wander farthest from the truth.