There are biochemical differences in the brains of men and women determining their behaviour
Due to hormonal differences, the development of the human brain varies in males and females, determining their gender.
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Sexual differentiation of genitalia takes place within the first two months of a pregnancy. The sexual differentiation in the brain begins to only take place in the second trimester. Testosterone determines whether the brain develops as a male or female. These differences determine sexual orientation and gender identity.  Hypothalamic differences show the variation. For example, the preoptic area which regulates mating behaviour is 2.2 times larger in a male with twice as many cells. This depends on the number of androgens. These differences become apparent at the age of 4. After the age of 4, the number of cells in this nucleus decrease for females. These differences impact several functionalities and the sexual preferences of the individual. 
It is averred that the differences in the brain are negligible as there are no significant differences based on sex alone. This distinction between the male and female brain seems to suggest that all males think and operate on one level and all females think and operate on another. There are variations and differences in thinking, aptitudes and personalities, which need to be considered. The biological distinction between a male and female can actually be harmful as it suggests that one gender may not have the aptitude for something that the other has, when that is simply not the case.