Os zygomaticum bipartitum: frequency distribution in major human populations.

The frequency of the Os zygomaticum bipartitum was examined in major human populations around the world. Eastern Asians have a higher frequency of the bipartite zygomatic bone than any other geographical groups. The arctic peoples, Amerindians and the Oceanians, who all may have derived from eastern Asian population stocks, have a considerably low frequency of this trait. The frequency distribution from East/Southeast Asia to Africa and Europe through South/Central/West Asia suggests some clinality for the bipartite zygomatic bone. The second peak in the frequency is seen in Subsaharan Africa. The clinal variation with no identifiable regulation by subsistence patterns and environmental factors suggested a genetic background for the occurrence of the Os zygomaticum bipartitum.