I do wonder whether counting artificial categories is the right measure. Let's take the mammoth - it's basically a hairy elephant and the genetic material that

I do wonder whether counting artificial categories is the right measure. Let's take the mammoth - it's basically a hairy elephant and the genetic material that could make one is 99+% present in Asian elephants ( possibly 100%, just not all in the same individual ) today. A bit of selective breeding and you could probably produce one quite quickly [1] ie the true measure of diversity is the pool of genetic diversity out there - rather than some arbitrary classifications. [1] Look at the variety in shape and form of domestic dogs - they all came from the same stock a mere 20-40K years ago.