What amount of genetic variance between two groups of humans would account for / trigger a classification of a different species?

That is, is there a quantifiable amount of variance between say, a fruit fly and a different kind of fly, beyond which it is apparent they are two different species? Something like "2% of genetic variance, therefore a new species"?

Any sort of search on Google only turns up racist sites - apparently "genetic distance" is a codeword for rather unfriendly attitudes towards blacks - obviously I don't know the right technical terms to look for.