An occipital bun, also called occipital spurs, occipital knob, chignon hooks or inion hooks, is a prominent bulge or projection of the occipital bone at the back of the skull. It is important in scientific descriptions of classic Neanderthal crania. While not as prevalent among many of humankind's ancestors, primarily robust relatives rather than gracile, the protrusion is relatively common in modern Homo sapiens.
It is suspected that occipital buns might correlate with the biomechanics of running. Another as yet unsubstantiated theory attributes them to enlargement of the cerebellum, a region of the brain which mediates the timing of motor actions and spatial reasoning.
There are still some human populations which often exhibit occipital buns. A greater proportion of early modern Europeans had them, but extremely prominent occipital buns in modern populations are now fairly infrequent.
A study conducted by Lieberman, Pearson and Mowbray 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.
- PBS.org - 'Neanderthals on Trial' (January 22, 2002)