For all appearances, this looks like the skull of any human child. But there are two very special things about it. The first is that its owner was clearly deformed; its asymmetrical skull is a sign of a medical condition called craniosynostosis
that’s associated with mental retardation. The second is that the skull is about half a million years old. It belonged to a child who lived in the Middle Pleistocene period.
The skull was uncovered in Atapuerca, Spain by Ana Gracia, who has named it Cranium 14. It’s a small specimen but it contains enough evidence to suggest that the deformity was present from birth and that the child was about 5-8 years old. The remains of 28 other humans have been recovered from the same site and none of them had any signs of deformity.
These facts strongly suggest that prehistoric humans cared for children with physical and mental deformities that would almost have certainly prevented them from caring for themselves. Without such assistance, it’s unlikely that the child would have survived that long.
Be it in sports or comedy, they say that timing is everything. In evolution, it’s no different. Many of the innovations that have separated us from other apes may have arisen not through creating new genetic material, but by subtly shifting how the existing lot is used.
Take our brains, for example. In the brains of humans, chimps and many other mammals, the genes that are switched on in the brain change dramatically in the first few years of life. But Mehmet Somel from the Max Planck Institute for Evolutionary Anthropology has found that a small but select squad of genes, involved in the development of nerve cells, are activated much later in our brains than in those of other primates.
This genetic delay mirrors other physical shifts in timing that separate humans from other apes. Chimpanzees, for example, become sexually mature by the age of 8 or 9; we take five more years to reach the same point of development.
These delays are signs of an evolutionary process called “neoteny“, where a species’ growth slows down to the point where adults retain many of the features previously seen juveniles. You can see neoteny at work in some domestic dog breeds, which are remarkably similar to baby wolves, or the axolotl salamander, which keeps the gills of a larva even as it becomes a sexually mature adult. And some scientists, like the late Stephen Jay Gould, have suggested that neoteny has played a major role in human evolution too.
As adults, we share many of the physical features of immature chimps. Our bone structures, including flat faces and small jaws, are similar to those of juvenile chimps, as is our patchy distribution of hair. A slower rate of development may even have shaped our vaunted intelligence, by stretching out the time when we are most receptive to new skills and knowledge. Somel’s research supports this idea by showing that since our evolutionary split from chimpanzees, the activation of some important brain genes has been delayed to the very start of adolescence.