As much as I'd like to rearrange his testicles, he's probably right.
Male IQs have a flatter distribution, so more smart outliers - plus, they're more willing to singlemindedly follow an interest. (Ever try to get a remote control away from one? Now substitute "math problem" for "remote".) Females tend towards a more integrative mindset, which would rather write poetry, shower, etc. every so often. It's different. Not bad overall, just different.
Culture may have a role, but it ain't everything. When I did science contests abroad, I was always struck by the chicks from places like Saudi Arabia, running around in full hijab and not even allowed to shake our guys' hands. And they did fine. That's hardcore. Did Barbie really fry our circuits that badly?
I did a lot of high-level science competing back in the day. It's a small subculture; we mostly know each other, two degrees of separation max. And the only gender ratio approaching 50:50 was the ratio of X to Y chromosomes.
I was pretty good, and I worked hard - saying I must suck because I'm a girl is like saying Yao Ming must be short because he's asian. But some of those guys were
insane, much better than me. That's Harvard's future professor pool, and it isn't Harvard's fault that various ratios just aren't there.