Species evolve by nature selection; that’s what makes species adapt and change to their environment, the individuals with the best characteristics to their surroundings survive and breed, the others just die, eliminating in the process unwanted and weakness in the specie itself.
Humans don’t do that, everyone breeds, people with permanent sickness, short sighted people, people who have a higher potential of cancer, etc. etc.
The only reason that they still breed is our humanity, and our love to help others.
Imagine that we aren’t human, a lot of genetic diseases would be phased out.
Let me take the example of myopia, I used to have myopia before my surgery (I still have traces), like 100,000 years ago I wouldn’t survive in the wild, I would be eaten by some saber tooth simply because I cannot see it coming :P.
For some reason myopia is still here, probably because some 100,000 years ago they found some useful work for people with myopia instead of letting starve to death…
which is good on a humane level, and probably people with myopia instead of hunting were left thinking in some corner and invented some nice stuff, but on the genetic level…what a disaster…
I think we discovered the fire too soon :P.