For anthropology professor Jeremy DeSilva, the evolutionary lineage of human beings hold a special allure. DeSilva specializes in human evolution and the anatomy of proto-human species, particularly the origin and evolution of bipedalism. DeSilva recently coauthored a special issue of the journal “PaleoAnthropology,” focusing on Australopithecus sediba, a two million-year-old potential human ancestor found in 2008 in South Africa.
What fascinates you about paleoanthropology and the study of ancient bones?
JD: What really fascinates me is that each of these bones — whether they are tiny little bits of a backbone or whatever it is we find — those were the remains of our ancestors. I think what really compels me is that each one of these bones tells a story about our past and helps reveal how we are the way we are today. I can’t imagine a more compelling question to ask. Why are we here? Why are we the way we are? And one of the ways we get at that is by investigating these incredibly rare, fragile remains that are so packed with information.
Who was Australopithecus sediba?
JD: Sediba is a species in a group called Australopithecus, and Australopithecus was a kind of early human that lived between two and four million years ago. What we know about Australopithecus is that they walked on two legs. They left us footprints — their knees, hips and their feet would all suggest they walked on two legs, but they still had a small brain.
What are some things that the species’ discovery reveals about human evolution?
JD: What we’re learning is that Sediba has a brain about the same size of a gorilla’s brain, but it’s not shaped like a gorilla’s brain. It’s actually shaped a little more like yours or mine. This is confirming, or at least supporting, some early ideas in our field that brain reorganization preceded brain enlargement, so that’s kind of an important realization about brain evolution. Brain reorganization and enlargement didn’t happen in lockstep.
What are some of the challenges of interpreting the bones of extinct species?
JD: There are enormous challenges. The way you move and walk is not just a function of your skeleton. It’s also muscles, tendons, ligaments and all the soft tissue in your body, and none of that fossilizes. So we have to make inferences. One of the other big challenges is that when we find fossils like this, you can’t ever put Sediba on a treadmill, right? They’re extinct and we will never know for certain how they walked — because we don’t have time machines — so what we have to do is rely on our understanding of how form can be used to infer or predict the functions of an organism.
What are the tools of your trade?
JD: The kind of work that I do honestly doesn’t require much. I need calipers and plane tickets. My calipers are my most trusted tool to take measurements of things, and these measurements matter. If you can quantify a size or a shape and compare that to humans and chimpanzees, it’s telling you something. So those are my most important tools — my calipers and the ability to travel to get to the fossil site.
What would be one of your “holy grail” finds — a breakthrough that you want to make?
JD: We have almost no idea what an ancestral chimpanzee looks like. We don’t have fossilized chimps. Part of the reason is that they lived in the forest and it’s harder for fossils to form or even be discovered in a forest. Also, we think fossilized chimps are probably located in some really unstable areas in Africa, so very few people are looking in these regions. But having a fossilized chimp would give us a sense of how much change they underwent in their evolutionary history. Because we have no fossilized chimps, we use modern chimps as a model and that’s very likely wrong.
This interview has been edited and condensed for clarity and length.
