Natures default gender setting is female. Though the male sperm supply the Y chromosome that determines the eventual gender of the fetus, a fertilized egg still starts off the first few weeks of life as female.

A large testosterone surge during the 8th week of pregnancy in the brain turns on the switch for a male infant.  If this increase in testosterone does not happen, then the fertilized egg continues to develop as a female.

What does an increase in testosterone do to the brain development of the female infant?

Testosterone basically kills of some of the cells in the communication centers and grow more cells in the sex and aggression centers for the male fetus.  This fork in our brain development establish our future.  It is not just the reproductive organs that make women and men so different.

Men pick up subtle signs of sadness about 40% of the time, while women pick up the signs 90% of the time.  With smaller communication centers in their brains, males are just clueless at picking up subtle emotional signs.

Differences in the adult brains of women vs. men

The male brains are larger than female brains by approximately 9 percent (after correcting for the larger male body size).  However, men and women have the same number of brain cells.  This means that women’s brains are more dense than male brains (think muscle vs. fat).  If you have more muscle mass, you will look smaller than a person with more fat, even if you are both the same weight.

The brain chemistry in menstruating women change by as much as 25% every month.  Though things get rocky at times, for most of us it is manageable.  Each hormonal phase (childhood, the teens, the dating years, motherhood, and menopause) causes fluctuation in our brain chemistry and how we view reality.

Men’s brain chemistry is like the mountain that is worn away with time by the weather and the movement of the earth (small stable changes).  Women’s brain chemistry, due to all the hormonal changes in our lifetime, is the weather that beats against the mountain.