Other: it's a huge mish-mash of interactions between different things in biology (hard-wired impulses that are different between sexes, AND the fact that male have only one X chromosome leaving to more recessive stuff), cultural stereotypes, game theory, patterns of social interaction - even if I had a clear model of the network of the causal relationships between all those factors, I still would find it hard to say whether under that model "variance in intelligence is caused by biology" would count as true or not.