A news story reporting that the NYPD re-mentioned to their officers that women could legally go topless in public has gone viral.
Everyone has an opinion!
There are many countries around the world where both men and women will be out in public topless, but since the US has traditionally only accepted males to go topless, this has caused quite a stir.
This post is less of a debate on topless laws, and more of an examination of this specific area of male and female anatomy.
So, what is the difference between a female and male mammary gland?
Not that much.
During the onset of puberty, male or female hormones either inhibit or signal branching differentiation of the ductal tree. ( -source)
Also during puberty, estrogen signals fatty tissue to form around the breast area in females. In addition to Cooper’s ligaments, this is what gives female breasts their shape.
Why do men have mammary glands and nipples?
There are a couple of theories to answer this question. The most widely accepted is that men have mammary glands and nipples simply because females do. The trait would have to evolve and “uncouple” in order for men to not have them:
“The only way such differences can evolve is if the same trait (color, for example) in males and females has become “uncoupled” at the genetic level. This happens if a trait is influenced by different genes in males and females, if it is under control of genes located on sex chromosomes, or if gene expression has evolved to be dependent on context (whether genes find themselves within a male or a female genome). The idea of the shared genetic basis of two traits (in this case in males and females) is known as a genetic correlation, and it is a quantity routinely measured by evolutionary geneticists. The evolutionary default is for males and females to share characters through genetic correlations.” – Andrew M. Simons, professor of biology at Carleton University
Basically, there isn’t enough reason for deselection of this trait in males for nipples or mammary glands to go away. The trait persists not only because of lack of selection against it, but there is strong advantage to males keeping their mammary glands – they have the ability to lactate. Although rare, male to female transexual parents are now using this once thought of vestigial part of their anatomy to breastfeed their children.
Why do human females have perennially enlarged breasts?
Check out any of the other Great Apes (or any other mammal) and you’ll find enlarged breasts in pregnant and lactating females only.
Unfortunately, no one knows exactly why this is, but there are, of course, very probable theories as to why this might be.
Evolution and natural selection works to our advantage, as it makes almost every part of our body have a function. When our species began walking upright, we had an entire area (the chest area) that served no helpful purpose in attracting a mate.
The theory that human females have permanently enlarged breasts suggests that this area of the body now could help attract a male, as this area was now focal when scanning a group of females, in addition to the buttocks.
Fat is Fetching:
In addition to the fact that this bare chest area of bipedal humans could be useful in attracting a mate, the reason behind enlarged breasts rather than brightly colored or other eye-catching features that could have adapted onto this area is because fat signals a high reproductive value for males.
Breast, buttocks, and hips are typical areas where human females store fat. There is a theory that these areas (which are unique to human females only for fat storing) were selected traits humans adapted due to male preference. (–”Breast asymmetry, sexual selection, and human reproductive success” by Moller, AP, Soler, M and Thornhill R)
It is hypothesized that male humans would prefer the fat stored in these areas because it appeared to give women a wider pelvis (less complications in childbirth) and larger breasts would signal larger mammary glands (which at one time did signal better lactation ability).
Breasts could just be another area of the body that symmetry can be displayed to attract a mate. Humans find symmetrical features more attractive, and asymmetrical breasts have been shown to be less attractive to males.
Breasts Allowed for Female Freedom.
Human females have concealed ovulation. Other primates like bonobos, baboons, and common chimpanzees have external signs of estrus to alert a mate of reproductive worth.
However, enlarged breasts typically are not seen as attractive to other primate species as it shows the female is either pregnant or lactating, which makes of very little reproductive value to the male.
So, as a benefit of concealed ovulation, the breast area adapted to have fat around it as a confusion signal to males, allowing them to be less closely guarded and available to multiple sexual partners for social, material, or genetic benefits. (-source)
The Nubility Hypothesis
This hypothesis suggests that permanently enlarged breasts in hominid females evolved as an honest signal of age, and thus, reproductive value.
This idea goes into detail about how pre-pubescent and post-menopausal women are infertile, and size and shape of breasts indicate to a male whether or not the female he is observing is of high reproductive value because her breasts give some signal of her age.
The reason the fat would specifically be in the mammary gland area was that it already coincided with menstrual cycle and aided in the signal of puberty.
No protrusion of breasts would indicate pre-pubescent (anovulatory) and not a reproductive match for a mating male.
Protruding firm breasts would indicate a mature (ovulatory) and reproductive match.
Sagging and thin-skin on breasts would suggest post-menopausal (anovulatory) and again, not a good reproductive match.
It seems, in this hypothesis, there is a trade-off of gaining maximum reproductive value during peak fertility, with less desired mates toward the end of her reproductive years.
Frank Marlow of the nubility hypothesis also offers information when given the argument of male cross-cultural breast size preference (it varies), but female breasts are an erotic stimulus for many cultures.
“Even though men’s interest in breasts may increase where women are clothed, the interpretation that men in nude cultures do not find breasts erotic is erroneous. Based on numerous interviews I conducted with the Hadza [ethnic group located in north-central Tanzania around the central Rift Valley], men find breasts erotic, even though women usually do not cover their breasts. They fondle breasts during intercourse [...]Such fondling is reported in numerous other nude cultures (Ford and Beach 1951). The contention that eroticism only occurs where breasts are covered would imply that men do not find vaginas erotic in completely nude cultures, and that there are no sexual signals among other species.” – Frank Marlow