Perhaps it’s time to prune the family tree. A 1.8 million-year-old skull suggests several of the half-dozen species of human ancestors and cousins alive then were likely all members of just one species: Homo erectus.
The skull was the fifth unearthed at a fossil-rich prehistoric watering hole in Dmanisi, Georgia; together, the specimens provide a vivid picture of the population of human ancestors at that location and place in time — and the variation within it.
The remarkably complete “Skull 5” features a big jaw, big teeth and overhanging eyebrows — but the brain was just one-third the size of a modern human’s. “Had Skull 5 been found as an isolated braincase and an isolated face, these parts may have been attributed to distinct species,” says Christoph Zollikofer, a University of Zürich anthropologist and author on the paper published in October.
The traits exhibited by Skull 5, and the less-complete skulls 1 through 4, are typically identified as belonging to three separate species within the Homo genus: erectus, rudolfensis and habilis. But the skulls show that characteristics often used to classify species actually occur within a single population.
The researchers are certain that Skull 5 reduces three classifications to one and suspect more Homo branches also might need to be clipped.
A second family-tree shake-up comes courtesy of a slightly older skeleton: the 2 million-year-old Australopithecus sediba dug up in Malapa, South Africa. In April, researchers completed analysis on the bones of the new species.
They found that some traits align with those of human ancestors: the shape of its jawbone and its affinity for walking on the ground. But other features — tiny chimp-like heels and shrugged shoulders — suggest it was too primitive to be part of the human family tree. Paleoanthropologists disagree on whether A. sediba is part of our direct lineage.
[This article originally appeared in print as "Skull Suggests One Homo Lineage."]
