Over a decade and a half ago Lawrence H. Summers, President, Harvard University, published his remarks about the shortage of women in science and engineering. He suggested that the innate aptitude of women was a factor behind their low numbers (The Math Myth, Time, March 28, 2005). Dr. Summers observed that women can't add two plus two as competently as men. His contention that men can process data faster than women because of their faster Nerve Conduction Velocity (NCV) is perhaps at best a highly intellectualised and debatable conclusion. NCV is not the only parameter that determines "intelligence". 

War of the sexes for dominance over the other has been on since ages, and Larry Summers view is a good exercise in igniting the battle. In this connection Yu Xie, a sociology professor, University of Michigan rightly states that any simplistic theory in this matter is doomed to fail.

Many biological factors play a role, and the final result is the interaction of biology with social conditions. Generally speaking, the brain of a female is more interlinked, and may be better suited for 'diplomacy'. Whereas, men are slightly more likely to say things without realising how their actions will affect others. 

Studies have shown that the corpus callosum, the bundle of nerve fibres that connects the two hemispheres of the brain was considered to be the key to intellectual development. It develops at different rates in boys and girls. The prefrontal cortex is the area of sober second thought, and women use it more often than men in conjunction with the amygdala which processes all 'emotions'. 

Men and women handle emotions differently. Studies have shown that men's brains are 10% bigger than women's brain, even when adjusted for the fact that on an average men are 8% taller than women. But the size does not predict intellectual performance.

By definition, intelligence is the capacity to acquire and apply knowledge, and an intelligence test establishes a rating by measuring a subject's ability to form concepts, acquire information, and perform other intellectual tasks. But all these data are arbitrary, and 'normals' are subject to a 'biological variation'. Moreover, in all these parameters a common denominator is "aptitude", which is the inherent learning ability, dependent on factors like 'heredity' and 'environment'.
 
Dr. Eric Berne, a psychologist, has presented an explanation at the cellular level. 

Initially the human embryo forms a three-layered tube. The inner layer grows into the stomach, lungs and other viscera; the middle layer into bones, joints and blood vessels; and the outer layer into skin and the nervous system. Usually these three grow almost at the same pace, and the average human being is a fair mixture of brains, muscles and viscera. Due to biological variations in some embryos, one layer develops more that the other, and the activities are mostly concerned with the overdeveloped layer.

Thus some people are mainly "digestion minded", some "muscle minded', and some "brain minded". Correspondingly we have 'viscerotonic endomorphs', the 'somatotropic mesomorphs' and 'cerebrotropic ectomorphs'. In addition, moving among us are 'normal' people. Thus unequivocal conclusions about relationship of sex with "braininess" is impossible. Rather it depends on training, heredity, nurture, and environment.