Subject: How can the mutation of a single individual give birth to a new species?

The random mutation of an individual might result in an advantadge that helps 
it survive better than it's congenres, so, out of natural selection, the 
species evolves a little bit. THe problem is, it sounds rather incredible that 
all, say, horses, come from a single ancestor that just happened to grow a 
tail. I would expect more genetic diversity to be necessary. Is that so? Thanks!

Re: How can the mutation of a single individual give birth to a new species?