Earlier quoted context omitted.
I don't think I've ever met a leftist denying evolution.
Me neither. Lots of them deny that certain differences between humanity exist however, and that's just biology. Eg. Fe-/male and racial differences. They exist, yet they cannot be admitted to and any reference to them will have the political left call you a nazi, racist, sexist and pedo to boot, because the other terms are already less impactful from overuse
Perhaps because, to many people, it seems wrong to set policy based on marginal differences in the aggregate when the policy will affect individuals, and also because people doubt the motives of those who are highly invested in proving a scientific basis for negative stereotypes.