Why Do Men Have Breasts And Nipples?
They're always right there, taunting us: why do you have me, they ask? Why do we men have breasts and nipples? The question has perplexed me for a long time (even great thinkers, from Aristotle to Darwin, have pondered over this question). So I set out in the journey to the deep wires of the Internet and here's what I found.
By Sadho Ram — 14 Sep 2014, 12:22 PM — Updated about 10 years ago
While there seems to be a pretty logical explanation behind why women have breasts and nipples (to feed babies), why do our bodies retain what appears to be redundant body parts?
The Darwinian natural selection process would seem to dictate that male nipples really should not be there. So what's the deal?
infinityhousemagazine.comBut before we begin, here's a fun fact:
Male mice exit the womb with their furry bellies smooth and nipple-free. Alongside stallions and male platypuses, mice are among a small cluster of mammalian species that don't go ahead and sprout nipples as though in symbolic solidarity with their female kin.
According to a Wikipedia entry about nipple in male mammals, from conception until sexual differentiation, all mammalian fetuses within the same species look the same, regardless of sex
In humans, this lasts for around 6 weeks, after which genetically-male fetuses begin producing male hormones such as testosterone. Usually, males' nipples do not change much past this point; however, some males develop a condition known as gynecomastia, in which the fatty tissue around and under the nipple develops into something similar to a female breast. This may happen whenever the testosterone level drops.
So here's the thing, as much as men might hate to hear this, the human fetal blueprint is initially female. We all begin as a ball of cells that quickly differentiates into various body parts.
At five weeks of gestation, the fetus sports a neural tube that eventually becomes the spine, but other than that, we all look like a wad of chewing gum. Then at six weeks' gestation, the outlines of eyes, arms, legs and a face (and let's not mention the tail that also shows up for a while) appear. It's not until about week six that the fetus also begins to take on the biological accoutrements of gender.
livescience.com
If the fetus has a Y chromosome, testosterone will turn the buds for sexual organs into testes. Once in operation, those testes will pump out even more testosterone and, voila, a penis appears. Female fetuses aren’t swayed by testosterone and so they stick with the fallback blueprint that calls for ovaries and a vagina.
But the developmental secret here is that breasts and nipples are already in place before testosterone shows its hand and starts shaping cells into male organs. In other words, men have breasts and nipples because they already had them before they became male.
livescience.com
Therefore, the simplest explanation for men having nipples is that all human embryos start out with them, and evolution didn't get around to selecting against their existence on the male bust. But why didn't evolution opt to remove them?
But because the "female template" is the default for humans, the question should not by why evolution has not selected against male nipples, but why it would be advantageous to select against male nipples? And it begins with:
The uncoupling of male and female traits occurs if there is selection for it: if the trait is important to the reproductive success of both males and females but the best or "optimal" trait is different for a male and a female. We would not expect such an uncoupling if the attribute is important in both sexes and the "optimal" value is similar in both sexes, nor would we expect uncoupling to evolve if the attribute is important to one sex but unimportant in the other. The latter is the case for nipples.
Their advantage in females, in terms of reproductive success, is clear. But because the genetic "default" is for males and females to share characters, the presence of nipples in males is probably best explained as a genetic correlation that persists through lack of selection against them, rather than selection for them. Interestingly, though, it could be argued that the occurrence of problems associated with the male nipple, such as carcinoma, constitutes contemporary selection against them.
As LiveScience notes, men's breasts, in fact, are a good lesson in the higgledy-piggledy way that evolution works
Natural selection chooses for and against body parts, but there is no master plan that aims for the perfect creature. Men have boobs, women get facial hair, and we all stand in front of the mirror asking, "Why?" Each person is, in fact, a Rube Goldberg sort of organism pieced together by biology and made up of good parts, bad parts and parts that are inconsequential.
livescience.com