Once reconstructed, it was clear that Karabo had arms suitable for climbing and a brain not much larger than a chimpanzee’s. But his teeth and hips were much like our own, his hands capable of toolmaking. He also had a unique, hyperpronating way of walking unlike anything seen before. Karabo’s anatomy was so peculiar that, had the skeleton not been found all at once, paleoanthropologists might have thought its various parts came from different species altogether.
“The foot had more primitive features than other hominids we think are primitive to this. The heel is chimpanzeelike,” says Berger. “That’s a problem. Because if you look at afarensis, Lucy’s species, that’s got a heel that’s like a modern human’s.”
“You have to start driving uncomfortable questions,” Berger says, “like maybe it’s coming from something we haven’t seen. Maybe there are other lineages out there.” Like Clarke, Berger believes the labels on the tree of human evolution could be wrong because we haven’t found all the species, or branches, that make up the tree. We may have attached evolutionary branches in the wrong places, building false relationships between species that didn’t give rise to one another.
Even more tantalizing were the results of a recent metaanalysis using 13 datasets, composed of 20 previously described hominin species and their fossils, and covering all 7 million years of human evolution. The study found Karabo most likely to be ancestral to the genus Homo — but not a descendent of A. africanus. The research, focusing on cranial and dental features, was the first of its kind to compare competing hypotheses on the relationships between various hominin species using a complex method known as Bayesian analysis. Despite the results, however, the issue of timing complicates our understanding: While Karabo was estimated to be living shortly before fossils of Homo show up in South Africa, there are Homo fossils in East Africa that precede it by hundreds of thousands of years.