Researchers led by University at Buffalo anthropologist Noreen von Cramon-Taubadel published a study in PLOS One arguing that the human chin evolved largely as a byproduct, not as a direct adaptation. The chin is unique to Homo sapiens and is absent in chimpanzees, Neanderthals, Denisovans and other extinct human species.
The team tested the null hypothesis of neutrality by comparing cranial traits of apes and humans. They report some evidence of direct selection on parts of the human skull, but traits specific to the chin region fit a spandrel model better.
The authors conclude that changes since the last common ancestor with chimpanzee likely reflect selection on other jaw and skull parts, and they say the results challenge an adaptationist tendency in anthropology while stressing the need to study trait integration.
Difficult words
- anthropologist — scientist who studies human origins and cultures
- byproduct — result that happens unintentionally during a process
- adaptation — trait that helps an organism survive or reproduce
- spandrel — feature that arises as a side effect, not purpose
- neutrality — state with no strong evolutionary change or selection
- cranial — relating to the skull or head bones
- selection — process where certain traits become more common
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Discussion questions
- Do you find the idea that the chin is a byproduct convincing? Why or why not?
- How might this study change the way people think about human evolution and physical traits?
- Can you think of another human trait that might be a byproduct rather than an adaptation? Explain briefly.
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