Stupid Question ™
June 27, 2002
By John Ruch
Q: Why are black rhinos and white rhinos considered different species and not, like humans, different races of the same species?
—Darwin and Greg
A: If you’re making an analogy between black/white rhinos and black/white humans, it’s a false one. Black and white rhinos are in fact the same color: gray (sometimes shading to yellowish brown for white rhinos).
The term “white rhino” is apparently a corruption of Afrikaans weit, meaning “wide,” referring to the animal’s broad snout. The black rhino was apparently named simply in contrast to “white” (though also possibly because it often wallows in dark mud).
The names tell us more about Western culture’s phony black-white dichotomies than it does about the animals’ relationships.
Ironically, while “species” is the basic unit of modern evolutionary biology, it’s been notoriously difficult to define.
The standard working definition comes from evolutionary biologist Ernst Mayr: a population of beings that share a common gene pool (common characteristics throughout the group, though not all are necessarily present in each individual); can “actually or potentially” interbreed; don’t breed with anything else; and inhabit a common ecological niche. All this also assumes descent from a common ancestor.
I won’t go into the problems with this definition, nor with the purely genetic alternatives. Suffice it to say that the ability (and desire) to successfully interbreed is still the litmus test for deciding whether a group is a distinct species.
As far as I can tell, white and black rhinos do not attempt to crossbreed in nature, nor has anyone attempted it in captivity. Barring experiments or DNA testing, it’s a good bet they would not successfully interbreed. (Such guesswork is typically considered good enough for species designation.)
Also, they have significant morphological and ecological differences. The black rhino is smaller, less muscular and has a prehensile upper lip, while the white rhino is massive and has a wide, non-prehensile mouth.
The black rhino is a browser on wooded hills; the white rhino a grazer on open plains. They likewise show significant differences from the Indian, Javan, Sumatran and Borneo rhinos.
African rhino species have “subspecies” (the technical term for “race”), used to identify localized groups with trivial physical or territorial differencers. “Race” and “subspecies” are both truly subjective terms of convenience.
Human “races” are just as subjective and are nothing like species. Clearly, we can all interbreed and do so all the time. No natural human group inhabits an ecological niche distinct from the rest of us. There are no significant morphological differences between “races.”
DNA analysis shows that differences in skin color, hair type and eyelid formation are genetic trivia that are never uniform enough to assign a strict “racial” classification. (As the evolutionary historian Stephen Jay Gould noted, there is no race gene.) It also shows that such distinctions have a fairly recent genetic history and occurred well after the formation of our overall species of Homo sapiens.