More than a century after Darwin, there are still serious
debates among biologists (and even more so among philosophers of
biology) about how to define species. Shouldn't
scientists define their terms? Yes, of course, but only up to a
point. It turns out that there are different species concepts with
different uses in biology -- what works for paleontologists is not
much use to ecologists, for instance -- and no clean way of
uniting them or putting them in an order of importance that would
crown one of them (the most important one) as the concept
of species. So I am inclined to interpret the persisting debates
as more a matter of vestigial Aristotelian tidiness than a useful
disciplinary trait.
Darwin's
Dangerous Idea, 1995
[on the search for 'necessary and sufficient
conditions']