Why do some babies develop penises and others don’t?
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Men and women have basically the same vital organs, blood vessels, flesh, and bones…but somehow, our genders are different. Why do men develop penises, and women don’t?
Lets start at the beginning—of life.
According to a report in IFL Science, the penis evolved as part of the process of procreation on land. Reptiles, for instance, often develop penises in twos, originating in the tissue that also becomes legs (a pair of legs = a pair of penises, apparently). Mammals, on the other hand, only get one, since our penises evolve from tail-bud tissue (one tail = one penis).
That’s evolution—now what about how those mammalian penises actually develop?
A baby’s genitals start to form during the 9th week after conception. Up until now, the baby has been neither male nor female. The baby only has what are called “indifferent gonads,” which have the potential to become either ovaries or testicles. At the same time, other internal features of both sexes develop–the Mullerian (female) ducts and the Wolffian (male) ducts.
The developing baby begins to form testicles if there is a y chromosome. The testicles release chemicals that turn the developing fetus into a boy. Testosterone, which is made by the testicles, makes the labia fuse together to make the scrotum and the penis. The clitoris becomes the glans (head of the penis), and the urethra lengthens. Mulerian inhibiting factor (MIF), also made by the testicles, makes the developing female ducts disappear—the vagina, uterus, and fallopian tubes go away. (Without testosterone and MIF we would all have female genitals.)
Although chromosomes provide the basic genital blueprints, the environment of the developing baby can also influence the end result. In addition, environment can have a significant impact on the “brain” sex of the person, or how the person identifies themselves in the spectrum from masculine to feminine. These “influencers” include the mother’s natural hormone levels, her exposure to medications and toxins, and even stress.
There is also evidence that the male brain is different in some ways than the female brain. For example, some scientists say that there is an area of a boy’s brain that makes him more interested in toys that propel, while a girl’s brain is wired more toward nurturing toys. There are also theories about differences in learning styles and strengths—men being hardwired to be better at spacial reasoning, for instance. Of course, there are societal pressures at work here as well, so the specifics of gendered brains are still uncertain, and the research continues.
For boys, the key element that shapes the brain is testosterone. It strengthens some brain connections and pares down others. But even if some structures of the brain are typical of males or females, every brain has both “male” and “female” elements.
There are some known conditions that affect gender, including “androgen insensitivity syndrome.” In this condition, the developing baby is genetically male with a y chromosome, but his tissues are not sensitive to testosterone. This means he doesn’t develop male genitals—but he doesn’t develop female internal organs such as ovaries, either. Instead, these individuals have female external genitals (labia and clitoris) but the vagina is short, and there is no ovaries, uterus, or fallopian tubes. They have testicles that are not descended since there’s no scrotum to descend into. They also experience female-like breast development due to testosterone being converted to estrogen.
Another condition, known as “Guevedoce,” or “penis at twelve,” is a genetic condition most commonly seen in the Dominican Republic. One out of every 90 boys is known by this term, which means they don’t develop a penis until age twelve. Until then, they appear (and are raised as) female.
These boys are deficient in an enzyme called 5-a-reductase, which usually converts testosterone into dihydro-testosterone, which is even more powerful than testosterone when it comes to stimulating the formation of the penis and scrotum from the labia and clitoris. As a result, the babies are born with female appearing genitals. When puberty comes around, the child gets a much bigger hit of testosterone from his testicles, resulting in the completion of the formation of the penis. .
Beyond this nontraditional start to life, the Guevedoce don’t experience any sort of negative physical side effects. They go on to live normal lives as men, though their facial hair is a bit sparse, and their prostates are a bit smaller.
There are other instances of unusual gender presentation, too. Congenital adrenal hyperplasia, a disorder of the adrenal glands, can cause a female baby to have a high amount of the male sex hormone testosterone in their bodies. For female children, this might manifest in female genitals that look more like a penis at birth. All of this can lead into the controversial topic of gender reassignment surgery in newborns. Should babies with atypical genitals undergo surgery to look more “male” or “female”? It’s an issue that’s under a lot of scrutiny these days.
The process of development may be a bit different from individual to individual, but in the end, gender comes from a variety of places both on the inside and the outside of the body. Complex interactions between hormones and chromosomes create, for some, the penis. Keep it healthy and happy, and you’ll have a lifelong companion.