Rufous-crowned Sparrow

So marked is variation in some bird species, such as North America's white-crowned sparrow and Eurasia's yellow wagtail, that experienced birdwatchers can identify an individual bird's approximate birthplace by its plumage pattern. Variation in apes encompasses many of the same characteristics that vary geographically in humans. For example, among the three recognized races of gorillas, western lowland gorillas have the smallest bodies and rather grey or brown hair, while mountain gorillas have the longest hair, and eastern lowland gorillas share black hair with mountain gorillas. Races of white-handed gibbons similarly vary in hair colour (variously black, brown, reddish, or grey), hair length, tooth size, protrusion of the jaws, and protrusion of the bony ridges over the eyes. All these traits that I have just mentioned as varying among gorilla or gibbon populations also differ among human populations. How does one decide whether recognizably distinct animal populations from different localities constitute different ...»