A single gene controls much of the development of the human face. The same gene is also involved in the domestication of dogs – suggesting that we have domesticated ourselves as a species.
The finding is one of the first pieces of hard evidence for the idea that humans are self-domesticated.
Over generations, humans have evolved less aggressive behaviours and appearances, says Giuseppe Testa at the European Institute of Oncology in Milan, Italy. This paved the way for large-scale societies in which thousands or millions of people cooperate.
Domestic animals are recognisably different from their wild cousins. For example, dogs’ faces are relatively short compared with wolves, and they often have small teeth and floppy ears. Domestic animals also tend to be more sociable towards humans.
Human faces look similarly “domesticated” compared with other hominin species, such as Neanderthals. Our faces are flatter and don’t have prominent brow ridges – and we are unusually social and cooperative. As a result, some scientists suspect that before we domesticated dogs and cattle, we first domesticated ourselves.
Genes for friendliness
All the parts of the body that are affected by domestication are derived from a single cluster of cells in the developing embryo called the neural crest. This implies that changes to the neural crest might underlie domestication. By studying the genes that control the neural crest, some biologists hope to show that the same kinds of genetic changes are behind the domestication of dogs and humans.
Testa’s team studied a gene called BAZ1B, which is known to be involved in controlling the neural crest. BAZ1B is crucial for the development of the face. It belongs to a cluster of genes on chromosome 7, mutations in which cause Williams syndrome, a genetic disorder that causes distinctive facial characteristics and hyper-sociability. The dog version of the gene has been linked to domestication.
The researchers knocked out the gene in stem cells, which can develop into any body tissue, in developing embryos. As a result, the neural crest was slow to form and didn’t develop properly.
The team found that the activity of 448 genes was affected, suggesting BAZ1B controls all of them. “BAZ1B sits on top of a hierarchy of many other genes,” says Testa. “This gene is a master architect of the cranial neural crest.”
Many of the genes regulated by BAZ1B had already been identified as significant in recent human evolution, because we have different versions of them to those carried by Neanderthals. That the genes only evolved recently and are involved in controlling face shape adds evidence to the idea that humans are self-domesticated, although the picture remains incomplete.
It isn’t clear how much BAZ1B also contributed to humans becoming more sociable and friendly. “There is evidence that BAZ1B is involved in the development of the brain,” says Testa, which is suggestive that it was involved. However, he says changes to our faces and brains may have occurred at different stages of our evolution.
This study provides a greatly improved test of the hypothesis that sapiens differs from Neandertals and Denisovans by having been self-domesticated, says Richard Wrangham at Harvard University. As genetic tests improve we will be able to probe the idea further, he says.
Journal reference: Science Advances, DOI: 10.1126/sciadv.aaw7908
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