The human race as we know it today, doesn't have dozens of generations. We'll be a radically different species in just 200 to 300 years, through self-controlled evolution that has already begun.

Before the end of this century we'll be directly editing the genome of every child born in the first world. Human evolution is no longer in nature's hands, and it will never be again unless technological progress rolls backwards drastically (at the rate it's accelerating, that is possible but unlikely; it's more likely we're about to achieve lift-off in regards to rapid evolution; if you think CRISPR is interesting, just wait until you see what we have in just 30 years).