A minor point but maybe an important one: I wasn't actually wondering, because it doesn't matter, I think. There's enough reason to believe that this phenomenon exists, in aggregate, between most men and most women. There's been no explanation for it offered that holds that the effects are
just (e.g., something that claims that men's work output is correspondingly greater, or their need for income is). So whether it is nature or nurture, unless we think Google can fix the root cause, the right thing for Google to do is accept that the phenomenon exists and work around it. They don't need to track the phenomenon down.
It's like how Google focuses heavily on technical interviews over college GPA or even college degree. They've found that having a degree and a good GPA is not well-correlated with what they're hiring people to do. They could put a bunch of work into fixing the college system, but instead they design their hiring process to take it into account as little as possible.