Tyler Cowen cites a very good sentence from Matt Yglesias:
Liberals tend to believe that sexual orientation is determined by genetics but that gender-difference in behavior is not, whereas conservatives tend to believe the reverse.
Randall Parker (FuturePundit) followed up that liberals only pretend to believe in natural selection:
Also, liberals do not favor policies that will stop natural selection. Rather, they favor policies that will stop some suffering in the short run but which will cause dysgenesis. We are DEVO. D-E-V-O.