The human chin: an evolutionary byproduct ^{CEFR B2}

A study led by Noreen von Cramon-Taubadel at the University at Buffalo and published in PLOS One argues that the human chin is best understood as an evolutionary byproduct rather than a direct adaptation. The chin is a bony projection of the lower jaw and is unique to Homo sapiens; chimpanzees, Neanderthals, Denisovans and other extinct human species lack a true chin, so it helps identify our species in the fossil record.

The researchers tested the null hypothesis of neutrality by comparing cranial traits of apes and humans to see whether changes in the chin region follow a random model or show signs of direct selection. They report some evidence for selection on parts of the human skull, but chin-specific traits fit the spandrel idea better. The team uses the term spandrel, following Stephen Jay Gould, to describe a structural side effect similar to the triangular spaces that arches produce in San Marco Cathedral.

The authors conclude that changes since the last common ancestor with chimpanzee likely reflect selection on other parts of the jaw and skull, not on the chin itself. They say the results challenge an adaptationist tendency in anthropology and underline the importance of assessing trait integration when studying physical evolution. Source: University at Buffalo.