Occipital bun

Occipital bun is a morphological term used to describe a prominent bulge, or projection, of the occipital bone at the back of the skull. The term is most often used in connection with scientific descriptions of classic Neanderthal crania. While common among many of mankind's ancestors, primarily robust relatives rather than gracile, the protrusion is relatively rare in modern Homo sapiens.

Some scientists suspect occipital buns might correlate with the biomechanics of running. Another theory attributes them to enlargement of the cerebellum, a region of the brain which mediates spatial reasoning, motor function, and many aspects of brain wave patterns, including gamma waves.

There are still many human populations which often exhibit occipital buns. A greater proportion of early modern Europeans had them, but prominent occipital buns even among Europeans are now relatively infrequent. They are still found fairly often among Basque, Lapp and Finn individuals. Bushmen from South Africa and Australian aborigines often have occipital buns also. A rare occurrence is found in the north of England where the occipital bun is widespread in south Lancashire.

A study conducted by Lieberman, Pearson and Mowbray (Journal of Human Evolution (2000) 38, 291-315) provides evidence that individuals with narrow heads (dolicocephalic) or narrow cranial bases and relatively large brains are more likely to have occipital buns as a means of resolving a spatial packing problem.