Does evolution require a reduction in genetic diversity? Yes. (Well, technically it's not required... but realistically-practically... it's going to happen).
Does evolution require an increase in genetic diversity? Yes. (Again, technically no... but without it, all things would die rather quickly).
The only question is: Which is greater? What is the
net result?
Does evolution require a
net reduction in genetic diversity? No.
Does it happen? Yes.
When it happens continuously, creatures die off. This has happened, does happen and will continue to happen many, many times.
Does evolution require a
net increase in genetic diversity? No.
Does it happen? Yes.
When it happens continuously, creatures flourish. This has happened, does happen and will continue to happen many, many times.
The facts are that both these situations happen at different paces to different groupings of creatures all over the planet.
Some are lucky and flourish, others... not so much.
It should also be noted that any particular, specific increase or decrease in genetic diversity really says nothing about any overall
net increase or decrease on the populations in question.
Edited by Admin, : Add emphasis around "net".