Why stop at two genders?

All humans start as the same raw brain in the first few weeks in the womb and express gender characteristics (chromosomal, gonadal, endocrine, morphological, genital and brain gender identity) based on a known blueprint of hormone baths over the next weeks and years.

This suggests that other kinds of humans could possibly be created, including other genders or specializations of genders, by administering other hormones, other doses of hormones or stimulating other brain areas. As testosterone shrinks the communications center and expands the fear and aggression center in the male brain, so could some other hormone influence other areas of the brain, stimulating olfactory centers, for example, to improve the perceptual survival capacities of space colony dwellers.

Many forms of hormone management are already in use and it is likely that the area will become much more understood, manipulable, acceptable and normal including such techniques as continuous menstrual suppression in females, testosterone suppression in males and in-body auto-regulators for a variety of medical purposes. Designer hormones would follow in lockstep with designer genes.