The androgen testosterone is a male hormone. It's responsible for the development of many physical and psychological male features. While individual men secrete different levels of testosterone, it's quite rare that a man secretes none at all. Still, if a man has no testosterone in his body or he's unable to respond to the testosterone produced, he will fail to develop in many important ways.
Development of Fetal Female Physical Traits
Male fetuses begin to secrete testosterone around the sixth or seventh week of gestation. If, for whatever reason, they do not produce the hormone, they don't develop into males. More frequently, male fetuses may produce normal levels of testosterone, but their body cells won't be receptive to the hormone, which produces effects identical to those created by the absence of the hormone entirely.
According to Dr. Lauralee Sherwood in her book, "Human Physiology," male fetuses without the ability to respond to testosterone are born looking like female babies. Female reproductive organs develop both internally and externally, and until puberty makes it clear that the "female" child isn't entering normal female puberty, the child appears to be completely normal.
Development of Female Mental Traits
Physiologically, explains Dr. Sherwood, babies "default" toward female development. This means that in the absence of testosterone, not only will a baby's body develop into that of a female, but its brain will as well.
In their book "You: Having A Baby," Drs. Michael Roizen and Mehmet Oz explain that testosterone causes the fetal male brain to lose neurons in the communication center and develop more brain cells in the aggression center. In the absence of testosterone, these changes don't occur. Babies' brains develop with more communication neurons and fewer aggression neurons. Further, testosterone secreted in puberty exacerbates these changes. In its absence, the aggression center of the brain remains relatively small.
Female Maturation at Puberty
Testosterone changes the body of a boy into that of a man at puberty, explains Dr. Gary Thibodeau in his book "Anatomy and Physiology." In the absence of testosterone, characteristic adult male features like thicker musculature and body hair don't develop. A boy's voice stays high like that of a child, and his testes and penis don't grow. He is not capable of producing sperm or fertilizing an egg since it takes testosterone to stimulate the testicular cells to make sperm and semen.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "You: Having A Baby"; Michael Roizen, M.D. and Mehmet Oz, M.D.; 2009
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
