How does variation in Homo sapiens compare to variation in other species?
The fact that any two humans are approximately 99.9 percent identical at the DNA sequence level indicates that we are genetically quite similar to one another. To put this into perspective, however, one needs to compare the average nucleotide diversity in humans (about 1/1300 base pairs) to the levels of nucleotide diversity in other species. Such comparisons have been done using blood group and protein polymorphisms, but these comparisons suffer from potential biases: the loci were identified originally on the basis of their extensive variation in one species (typically humans), so they often exhibit more variation in that species. A better approach is to identify a specific region of DNA and then sequence it in large, random samples from multiple species. This has been done, to some extent, with mitochondrial DNA, where comparisons suggest that humans are substantially less variable than other primates. (On the other hand, humans have more diversity than animals, such as cheetahs, th
