Palaeontologists who have analysed the world’s largest collection of hominid fossils, including 17 430,000-year-old skulls excavated from a cave in northern Spain, conclude that these proto-Neanderthals developed their characteristically massive jaws, teeth and brows relatively early in their evolution – while they retained a brain case characteristic of more primitive species.
This view of Neanderthal history emerges in a paper published in the journal Science by the Spanish team working at Sima de los Huesos (Pit of the Bones), which has produced more ancient hominid bones than any other palaeontological site. The study confirms a “mosaic” evolutionary pattern. Rather than changes occurring steadily across the skull over time, some parts evolved very fast while others remained almost constant.
The Sima de los Huesos people seem to have been on the cusp of evolution from an earlier species, Homo heidelbergensis, which lived in Africa and Eurasia 500,000 years ago, to Homo neanderthalensis. Their bones show facial features and teeth markedly different from previous hominids, while the back of the skull is little changed.
Many of the Neanderthal-type features revealed in the study were related to mastication or chewing. “It seems these modifications had to do with an intensive use of the frontal teeth,” says Juan-Luis Arsuaga of Madrid’s Universidad Complutense, lead author. “The incisors show great wear as if they had been used as a ‘third hand’, typical of Neanderthals.” In particular, they were likely to have gripped large hunks of meat between their front teeth, which they cut up with stone tools.
An interesting feature of the Sima skulls is their homogeneity. Although there are differences in size, the shape is remarkably constant – in contrast to another famous hominid site, Dmanisi in Georgia, where researchers last year reported great variety among five 1.8m-year-old Homo erectus skulls.
It took 300,000 more years for classic Neanderthals with larger brains to evolve. They dominated human life in Eurasia until Homo sapiens, our ancestors, swept in from Africa less than 80,000 years ago. The last Neanderthals died out 20,000 to 30,000 years ago in the Iberian peninsula, their last refuge.
Commenting on the Science study, Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig points out the high speed of human evolution over the past half-million years compared with other mammals. There are a few other examples of such rapid divergence – polar and brown bears are one – but chimpanzee and bonobo skulls are very similar in shape although the two species have been separate for two million years.