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First of all, hormones are the most significant determinant for sexes. Nature's first intention is to create a female (Adams 4). Furthermore, some addition is needed to create a male is created. So, the first distinction is observed while the baby is created. This is the first step for differentiation between the sexes. Moreover, males and females are different in terms of chromosomes. Women cells only contain X sex-determine chromosome while men carries X and Y. As it seen, nature is creating a difference between the sexes. After that point, male fetus create his own hormones and female fetus create her own hormones. In the second step for discrimination, for male fetus, hormones masculinize the brain and organize the fatal nerve centres in characteristic ways. On the other side female fetus also feminized the brain (Adams 5). The characteristic changes are also reason for menstruation or lactation in women and also growing beard for men (Hall 2). For this reason, it can be understood from this example that hormones create some differences between the sexes in terms of physical appearance and characteristic property. For instance, men mostly have bristle and women feel emotional when they menstruate. In addition to this, hormones change the size of the cortex as well (Weintraub 20). Thus, it causes some parts to work more functionally than the others in brain functions which will discuss in the next paragraph. To conclude all, hormones create the first differentiation and more significantly it affects the head of nervous system, most important organ for humans, brain. .
Second step for discrimination between sexes are created by brain activities. Masculinization or after feminization, both of genders' brain starts working in different ways. Neurobiologist Donald Pfaff from Rockefeller University, proves that hypothalamus which is a primitive structure at the base of the brain stem, is effected by hormones and this let sex hormones control aggression and even fear (Weintraub 17).
