I find it funny that so much scientific research attempts to prove the existence of a biological contrast that's blatantly obvious, but which has been completely deconstructed and obscured by modern literary theory/philosophy.
The real problem is that our society tends to equate sameness with acceptability as its preferred mode of "tolerance". This has the paradoxical effect of re-inforcing the negative ways we view our differences (e.g. discrimination). That is, the desire to claim that we are all exactly the same is an implicit statement that it would be somehow problematic if we were not.
So, the fact that we are obviously different means that we are attempting to sell oursleves a lie that we never buy, while allowing our negative feelings about our very real differences go unchecked.