A species definition for the modern synthesis.

One hundred and thirty-six years since On the Origin of Species 3., biologists might be expected to have an accepted theory of speciation. Instead, there is, if anything, more disagreement about speciation than ever before. Even more surprisingly, 60 years after the biological species concept, in which species were considered to be reproductive communities isolated from other such communities, we still do not all accept a common definition of what a species is. And yet, if speciation is to be any different from ordinary evolution, we must have a clear definition of species. The emerging solution to the species problem is an updated, genetic version of Darwin's own definition. This definition is useful and is already being used in taxonomy, in biodiversity studies and in evolution.