Breed is more accurate than species here. Best definition I can come up with for breed is a set of geographically concentrated traits, often distinguishable by visual qualities. Think dogs: coloration, face shape, hair color, stature.
The major scientific requirement for speciation is sexual isolation: distinct species cannot reproduce between their populations. Highly similar populations can often reproduce but yield sterile hybrids. Considering the viability of mixed-race offspring among humans, it's inappropriate to consider other races as different species.
[–] ditch-digger 0 points 2 points 2 points (+2|-0) ago (edited ago)
Incorrect.
http://rafonda.com/interbreeding_between_species.html
[–] jxfaith ago (edited ago)
How is
Contradicted by
I am aware of wolves, coyotes, etc, crossbreeding. I would consider that broadly the biological exception to the rule. My statement, while perhaps not as logically formal as the textbook definition you provided, works sufficiently in almost every case. When last this topic came up (as it seems to be a rather popular pet argument for some people on this site), I wasn't able to dig up any other examples of extant species interbreeding. At least none as well-documented as coyotes/wolves/dogs. And even so, such hybridization is an exception rather than a norm. A modest percentage of individuals per generation, to my understanding. Certainly on a different level than interracial marriage among humans.