In the beginning, mannishness starts with a pairing of the robust X chromosome with the considerably smaller and more simplistic Y chromosome. Because the evolutionary history of the Y chromosome is one of decay and loss of genetic material, it has been argued that the Y chromosome may eventually disappear. Men, it would appear, are not just genetically mutated women, but they may also be endangered.
Yet, here we stand. If you are a man and have survived the chromosome gauntlet, then it looks like smooth sailing from this point on, right?
Sadly, no. Now you must survive the most terrifying trial of them all — testosterone.
During approximately the first six to eight weeks of life, male and female embryos are similar in feature and development. Then, as the embryo moves toward the fetal stage, the male fetus produces an increase in testosterone. Female fetuses do not. Because this hormonal change occurs early and during an important stage of development, it has been suggested that testosterone not only prompts changes in the physical characteristics of the male fetus but may also have a long-term effect on male brain development and subsequent behavior.
Depending on your perspective, this process either represents a normal prenatal stage in male development or is akin to a hormonal hostage taking of the fetal brain. For example, in The Female Brain (2006), Louann Brizendine states:
- Until eight weeks old, every fetal brain looks female—female is nature’s default gender setting. If you were to watch a female and a male brain developing via time-lapse photography, you would see their circuit diagrams being laid down according to the blueprint drafted by both genes and sex hormones. A huge testosterone surge beginning in the eighth week will turn this unisex brain male by killing off some cells in the communication centers and growing more cells in the sex and aggression centers. If the testosterone surge doesn’t happen, the female brain continues to grow unperturbed. (p. 14)
Others have been even more extreme. Greg Laden, in his science blog writes:
- The problem with men, as a group, as a type of organism, as a subset of humans, is that at various points along the way on their journey from the female template on which all humans are built biologically, they have been altered in ways that make them dangerous assholes. Even when we try to reduce the male-female difference as a society, men who do not willingly participate in that often end up being fairly nasty, dangerous beasts; they may be rapists, they may be batterers, they may be some other thing. They break our efforts to have an egalitarian peaceful world. In a way, they are broken. They are damaged, if you will. Some of that damage is facilitated by what you may know of as testosterone (a word that stands in for androgens).
It certainly makes great copy to anthropomorphize testosterone and imagine it as a barbarian horde trampling and pillaging across the unprotected female neuronal forest. So does envisioning testosterone as the wellspring of all that is violent, primitive, and thuggish in male behavior.
In reality, however, testosterone is no more aggressive or violent than estrogen is cuddly and nurturing. Testosterone is just one of the many chemical messengers used by your body to maintain its overall health and functioning.
Testosterone does play an important role in fetal sex differentiation. But its role in brain differentiation and the degree to which that differentiation reliably predicts future behavior remains far from crystal clear.
- Greg Laden: Men = Testosterone Damaged Women!
- Excerpt from Brizendine, L. (2006). The female brain. New York: Broadway Books.