What is the unit to use in evolution?
Well, I'd guess it would be something like change per generation. How to define either characteristic is up in the air, though generation seems basically like the average age before reproduction occurs in a species. I wonder how to take into account the range of ages. A woman can reproduce from like ages 12/13 to like 50, while men can reproduce pretty much well into their 70's and 80's.
There is the Evolutionary Significant Unit which is a subpopulation that is considered distinct from the larger species.