As 2012 nears its end, one thing stands out as the major theme in human evolution research this year: Our hominid ancestors were more diverse than scientists had ever imagined. Over the past 12 months, researchers have found clues indicating that throughout most of hominids’ seven-million-year history, numerous species with a range of adaptations lived at any given time. Here are my top picks for the most important discoveries this year.
1. Fossil foot reveals Lucy wasn’t alone: Lucy’s species, Australopithecus afarensis, lived roughly 3.0 million to 3.9 million years ago. So when researchers unearthed eight 3.4-million-year-old hominid foot bones in Ethiopia, they expected the fossils to belong to Lucy’s kind. The bones do indicate the creature walked upright on two legs, but the foot had an opposable big toe useful for grasping and climbing. That’s not something you see in A. afarensis feet. The researchers who analyzed the foot say it does resemble that of the 4.4-million-year-old Ardipithecus ramidus, suggesting that some type of Ardipithecus species may have been Lucy’s neighbor. But based on such few bones, it’s too soon to know what to call this species.
2. Multiple species of early Homo lived in Africa: Since the 1970s, anthropologists have debated how many species of Homo lived about two million years ago after the genus appeared in Africa. Some researchers think there were two species: Homo habilis and Homo rudolfensis; others say there was just H. habilis, a species with a lot of physical variation. It’s been a hard question to address because there’s only one well-preserved fossil, a partial skull, of the proposed species H. rudolfensis. In August, researchers working in Kenya announced they had found a lower jaw that fits with the previously found partial skull of H. rudolfensis. The new jaw doesn’t match the jaws of H. habilis, so the team concluded there must have been at least two species of Homo present.
The London Olympics are a great excuse to talk about England’s hominid history. Current evidence suggests that hominids reached Great Britain by at least 800,000 years ago, when the island was connected to mainland Europe. Since then, as many as four different hominid species have lived there. Coming and going in response to climate change, hominids probably fled England during extreme cold times when glacial ice covered the area. Sometime between 450,000 and 200,000 years ago, catastrophic flooding of a glacial lake eroded the land bridge connecting Great Britain and Europe and changed the drainage patterns of the region’s rivers. As a consequence, during warm periods when polar ice sheets melted and sea levels rose, the land bridge was transformed into a channel. This barrier probably explains why hominids are absent from the fossil record 180,000 to 60,000 years ago. It wasn’t until 12,000 years ago that the ancestors of modern Brits finally arrived on the island and stayed for good.
With that mini-review in mind, here are five of England’s most important human evolution discoveries.