Why do Women have breasts?

Paps Anu, Ireland (If you look closely, someone put nipples on top.)

Well, there’s a clickbaity title if ever I wrote one.

Nevertheless, human breasts are strange. Sure, all females of the class mammalia are equipped with mammary glands for producing milk, but humans alone posses permanent, non-functional breasts.

Yes, non-functional: the breast tissue that develops during puberty and that you see on women all around you is primarily fat. Fat does not produce milk. Milk ducts produce milk. They are totally different things.

Like all other mammals, the milk-producing parts of the breasts only activate–make milk–immediately after a baby is born. At any other time, milk production is a useless waste of calories. And when mothers begin to lactate, breasts noticeably increase in size due to the sudden production of milk.

A woman’s normal breast size actually tells you nothing at all about her ability to make milk–if anything, the correlation is the opposite, with obese women (with correspondingly large breasts) having a more difficult time nursing and producing milk:

A number of factors associated with low milk supply have been identified, such as nipple pain, ineffective nursing, hormonal disorders, breast surgery, certain medications, and maternal obesity. …  Research into breast size and milk production shows that milk supply is not dependent on breast size, but rather on the amount of epithelial tissue contained in a breast that is capable of making milk …

However, in addition to baby attachment issues, accumulating evidence shows that a major factor preventing overweight and obese mothers to breastfeed is the inability of their breast epithelial cells to start producing copious amounts of milk after birth. This is often referred to as unsuccessful initiation of lactation. …

a recent study took advantage of breast epithelial cells non-invasively isolated from human milk. In these cells, certain genes are turned on, which enable the cells to gradually make milk as the breast matures during pregnancy, and then deliver it to the baby during breastfeeding.

The study reported a negative association between maternal BMI (body mass index), and the function of a gene that represents the milk-producing cells. This suggested that the breast epithelial tissue is not as mature and ready to make copious amounts of milk in mothers with higher BMI. Most likely, the large breasts of overweight or obese mothers contain more fat cells than milk-making cells, which can explain the low milk supply of many of these mothers.

Therefore, breast size does not necessarily translate to more milk-producing cells or higher ability to make milk.

More fat=less room for milk production.

original source (colors have been changed.)

Interestingly, average cup size varies by country.  Of course the data may not be 100% accurate, and the lumping of everyone together at the national level obscures many smaller groups, like Siberians, but it otherwise still indicates some general trends that we can probably trust.

If breasts don’t actually make milk, then why on Earth do we have them? Why are women cursed with lumpy fat blobs hanging off their chests that have to be carefully smushed into specialized clothing just so we can run without them flopping around painfully?

And for that matter, why do we think they look nice?

One reasonable theory holds that breasts are really just front-butts. Our apish ancestors, like modern chimpanzees, most likely not copulate ad libitum like we do, but only when females were fertile. Female fertility among our chimpish relatives is signaled via a significant swelling and reddening of their rear ends, a clear signal in a species that wears no clothes and often walks on four limbs.

Le Chapeau, Peter Paul Rubens’s portrait of Susanna Fourmer

When humans began walking consistently on two legs, wearing clothes, and looking at each other’s faces, this obvious signal of female fertility was lost, but not our desire to look at rear-ends. So we simply transferred this desire to women’s fronts and selectively had more children with the women who piqued our interests by having more butt-shaped cleavage.

In support of this theory, many women go to fair lengths to increase the resemblance between their ample bosoms and an impressive behind; against this theory is the fact that no other bottom-obsessed species has accidentally evolved a front-butt.

I realized yesterday that there is an even simpler potential explanation: humans are just smart enough to be stupid.

Most of us know that breasts produce milk. Few of us really understand the mechanism of how they produce milk. I had to explain that fat lumps don’t produce milk at the beginning of this post because so few people actually understand this. Far more people think “Big breasts=lots of milk” than think “big breasts=lactation problems.” Humans have probably just been accidentally selecting for big breasts for millennia while trying to select for milk production.

Our breast obsession is cargo-cult lactation.


14 thoughts on “Why do Women have breasts?

  1. > Well, there’s a clickbaity title

    LOL. In the same way that “Hajnal Line” is clickbait for HBD Chick — I wanted to see what exolutionistx thinks about this topic.


    Liked by 1 person

  2. I think the standard sexual selection model makes more sense here. As soon as the phenomenon starts, sexual selection (“we have them because we think they look nice”) can develop it to indefinite heights. No different than funny hair colors. And like funny hair colors, bigger breasts can start out as a method of attracting attention by being unusual, and attention is valuable on the fundamentals.

    Liked by 2 people

  3. (For example, the “front butts” theory would predict that the aureole and the nipple are ugly; I don’t think the data bears this out. And I also don’t think that anyone was particularly trying to select for milk production — as far as I’m aware, that goal isn’t really attested at all. Compare “childbearing hips”.)


  4. Many trends in women’s fashion involve encumbering women in oversized or undersized garments so that they must exert special effort to walk and perform daily tasks. Konrad Lorenz included clumsy movement in his kindchenschema as a trait which evokes cuteness and nurturing behavior due to the association with how infants struggle to walk. My alternative explanation is that large breasts are perceived as cute because they are an encumbrance. Men fetishize physical “flaws” and character “flaws” that make women seem needy. Even if that means summoning “flaws” into existence or imposing “flaws” through cultural pressure.

    Liked by 1 person

  5. Is it possible that undersized breasts also correspond to insufficient milk production?

    Don’t think that obesity is attractive or healthy, but it could be a slight overcompensation for skinniness. Not that I have any data to back that up.


    • The data I have managed to gather on the subject says no, at least within the normal range of weights found in modern societies. Breast fat just isn’t milk ducts. Now, back when people faced famines more often, or sick/anorexic people today, extreme thinness probably did interfere with nursing–but at that point, it’s also interfering with menstruation and it’s going to be a lot harder to successfully conceive and carry a baby to term.

      Liked by 1 person

  6. >Why are women cursed with lumpy fat blobs hanging off their chests that have to be carefully smushed into specialized clothing just so we can run without them flopping around painfully?

    She doesn’t seem to mind: https://i.imgur.com/LJrHiXz.jpg and https://i.imgur.com/jl23xz9.jpg and there was some scandal about it at the Athens olympics, prudes objecting to the sight of breasts while the runner herself didn’t seem to mind the flopping.

    One possibility is a racial difference in the floppiness of breasts. Another possibility is that in a society that leaves breasts free and does not put them into halters at 15, some tissue develops differently.

    At any rate if Eritrean runner women don’t seem to have this problem, likely your ancestors didn’t either.

    Liked by 3 people

  7. Apart from breasts and wide hips the main difference between men and women is having less testosterone women are smaller more gracile and childlike than men. So men’s instincts are to be sexually attracted to these things. But there is a problem here those are also the traits of youths and children. So a caveman who is attracted to something only adult fertile women have wastes less of his time mating with children. This probably requires a scenario where women become fertile again while they are still breastfeeding and/or they pair bond long enough to make use of the next fertile period. Then once there are enough men around who like breasts the sexual selection cascade kicks in where women with decorative breasts attract more men and then men attracted to breasts do better as there are more breasted women around. With breasts and wide hips women look like 12 year old boys, so they need something to advertise that they are fertile women and any man attracted to something only fertile women have wastes less of his time with attraction to youths.

    Another idea that might for when people started pair bonding. A women gets pregnant she starts developing breasts so a boyfriend who likes breasts would then stay with his girlfriend longer helping her during her pregnancy, So if attraction breast growth lengthens a pre-existing relationship it improves the survival of that mans progeny.

    Liked by 2 people

    • At some point humans shifted from pheromones being important to visual cues being more important. Unlike chimps we no longer sniff vaginas to see if they are fertile. And most modern people dont seem to be that attracted to pubic hair and the associated adult body odor.


      • Ehh pubic hair was very common just 30 years go ago. Clean shaven pussy is new phenomenon. Daily showers(hell even weekly) is only slightly older


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