Why men are smarter than women

Lawrence Summers is considered one of the smartest economists of the world today. But his provocative but politically incorrect talk (In an age where political correctness borders on the ridiculous when it comes to gender, race etc.) at the NBER cost his Presidency at Harvard University and possibly a chance to become the current Treasury secretary. (I couldn't locate the original transcript of the talk anywhere. The NBER link is gone now)

Summers in his talk said innate differences in ability could explain why women are underrepresented in higher engineering and PhD programs. But what he was mentioning was not about the absolute differences in IQ, but their variances.

"If one is talking about physicists at a top twenty-five research university, one is not talking about people who are two standard deviations above the mean...But it's talking about people who are three and a half, four standard deviations above the mean in the one in 5,000, one in 10,000 class. Even small differences in the standard deviation will translate into very large differences in the available pool substantially out"

Studies have indicated that Men have higher variances in intelligence than women. This could mean at tail of the spectrum (dumb and the smart) men would outnumber women and at the extreme ends the difference would be stark.

What about average IQ? While some studies have said the average difference is miniscule, the recent ones does say that the difference could be significant. Santoshi Kanazawa, the evolutionary psychologist at LSE offers this explanation at his blog. Since taller people are smarter, and men are on average taller than women (this no one would deny), it could be the case that men are smarter than women, not because they are men, but because they are tall. He goes on to state that controlling for height, women are slightly but significantly more intelligent than men.

So why are tall people more intelligent? Heck, We could go on like this.