Another factor might be fat accumulation. As mentioned by others, the breasts contain a large amounts of fat. My general observation again has been that fat distribution can vary - some layer it on lower more on the butt, some higher, some around the middle, some mainly on the stomach, some all over… especially for women. Generally, men accumulate fat either mainly on the stomach, or all over. So there may not exactly be a breast-size gene as a “where shall I store accumulated fat” gene that gives a certain amount of preference to the breasts.
I’m not sure of this, so please, someone, help me out… But wouldn’t it be polygenetic? (As opposed to blue eyes, which are brought out by a single gene.) Like skin color: there isn’t just one gene for “dark skin,” but several genes, so you can get gradations of color.
Another argument for it being polygenetic is that mothers and daughters can differ very widely in breast size. There is some heritable correlation – larger mothers tend to have larger daughters – but there are so many exceptions that it can’t be a really simple genetic heritage.
Or maybe I’m wrong…
(ETA: also, diet, including some food additives/contaminants that are so influential, they gave even boys breasts.)
A bigger question is why do breasts make men act so dumb?
It’s been a while since I read it, but in socio-anthropologist Desmond Morris’ book *The Naked Ape *he posits the idea that large, permanently swollen human female breasts evolved after walking upright, as a way of mimicking the curvy round shape of a woman’s ass. IOW it makes her look sexy (while standing on two legs) from both front and behind.
I don’t know if there’s any official statistics, but I would guess that average size breasts are, well, the average. That overall they don’t really vary *that *much in size, that extra-large or small ones are statistical anomalies. But they all get noticed roughly equally because, well, guys are hardwired to notice them no matter what.
It’s basically a 3-way tie between Russia, Ukraine, and Poland for the highest per-capita concentration of beautiful women.
The short answer is because evolution never weeded out either small or large (or in between) breast sizes. As to why some women have huge ones is probably the bigger question since our ape ancestors have essentially none. Random mutation that does not increase the likely hood of an early death is a mutation that is likely to spread. If if confers an actually benefit to survival then it is very likely to spread.
or I have no idea either.
Genes come to a woman from her father as well as from her mother, remember.
If a daughter’s shape is unlike her own mother, look at her paternal female relatives. My sister and I are both about average to below average in breast size. My niece and my older daughter are both very well endowed. So were my mother-in-law and my sister’s mother-in law.
I remember shortly after my niece achieved puberty she walked past my sister and me as she was going outside to sunbathe. We both looked at her, and at each other, and commented, “Where did all THAT come from?”
Fair enough; but, again, how strong is the correlation? Is my notion of a polygenetic cause still viable?
(Also, the mother is the most significant relevant contributor, with aunts and uncles being only a quarter as relevant, with further halving at ever further distance along the family tree.)
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(Also, the mother is the most significant relevant contributor, with aunts and uncles being only a quarter as relevant, with further halving at ever further distance along the family tree.)
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No, because the father’s genes are just as significant. Just because they aren’t expressed in him doesn’t mean they aren’t there.
Looking at paternal relatives is just about trying to guess at what genes the father passed on. An aunt passed absolutely no genes to her niece.
Because they can. You’re misunderstanding genetics. Natural variation through random mutation will generally cause individuals to have quite significantly varying features, particularly for such simple characteristics as size. What natural selection generally does is rein in these variations, when they compromise some aspect of function that impacts survivability and breeding success. Hence, features of our genome that are absolutely mission-critical, e.g. certain basic enzymes for respiration, are exceedingly well conserved. No one has the slightest variation in them. Similarly, the size, shape and structure of the heart or airway or spinal cord is very consistent, since nearly any experiment along different lines is promptly fatal. In short, what needs evolutionary explanation in terms of functionality is uniformity of features, not variation. Variation is natural. Uniformity is not.
Breasts can vary in size wildly with essentially no impact on survivability. Furthermore, the existence of wide variation also implies that variation has almost no impact on breeding success, either (otherwise there would be selection for some optimal size). Which implies, as one might guess, that a woman’s breeding success is not significantly impacted by her breast size, within a wide range. In short, there’s a good supply of men who like them in almost any ordinary size.
By the way, an interesting side note on this is that breast size varies much more interwoman than intrawoman. That is, a woman may have big or small knockers, but her right is likely very close in size to her left. That actually needs explaining. Why the symmetry? It could be there is a significant hit on survivability (unlikely) or breeding success (seems more reasonable) with significant asymmetry. There is a general argument that humans are unusually sensitive to asymmetry and consider it ugly. I don’t think anyone has a good argument for why that would be, though.
But it’s also possible this occurs accidentally, e.g. that the same kinds of mechanisms control breast symmetry as control, for example, leg symmetry, which is clearly required for survivability. Hence the breasts are symmetric as an accidental side-effect of more essential symmetry, e.g. in limb size. But on the other hand, the human body has nontrivial asymmetry, e.g. in its internal organs, so why would symmetry of the breasts be a natural consequence of essential symmetry, when for example the lungs aren’t bound by it? If development mechanisms allow the lungs and neural circuitry to be asymmetrical, why do they not allow for significant asymmetry in boobs? It may indeed come back to the possible preference we have for breeding partners that look very symmetrical on the outside (we can see whether her nipples are on a perfect horizontal, but we can’t tell her liver is tremendously lopsided, so the liver is free to vary and seek some more optimal shape and location, while the nipples cannot).
Not sure how this relates, but I spent a couple of decades breeding goats, and naturally one chooses mothers who are the best milkers with the best “breasts”, udders. What I found, my experience has shown me, is that the daughters hardly ever will have the same udders as the mother. It’s a crapshoot. YMMV
At the risk of starting a whole new level of jokes, another organ which varies a lot in size (especially if we consider volume instead of just length) is the penis.
Which suggests to me the hypothesis that features that may have been subject to sexual selection in humans have gone through a lot of change in a relatively short time and therefore show a large distribution.
Then again, there are other, non-sexual organs showing a large distribution as others have pointed out (e.g. noses), so maybe there really is no anomaly to solve here?
I suspect that it’s closely related to the fact that our breasts are so much larger than those of our closest relatives (and correspondingly, than our fairly recent ancestors). We usually have big breasts because reasons, but we sometimes have breasts that are closer to chimp breasts (though very few women have breasts that are actually as small as a chimp’s).
The same reasoning could be applied to the penis.
And generally have less trouble with their new borns not suckling.
Europeans evolved in the land with lots of mammal domesticated animals and harsh winters.
WAG So the mother needed to store fat in obese amounts, to survive winter, and could feed the baby on animals milk if the fat destroyed her own mammary glands abilities. With the animal milk available, the babies that didnt suckle would survive and pass along the trait for lack of instinct to suckle the nipples of of an obese mother, and to be obese, to their descendants.!
Meanwhile in asia, no pressure to become obese, and a nonsuckling baby died.
Studies have shown people that are more symmetrical are rated as more attractive, possibly because more symmetrical people tend to have greater masculine or feminine characteristics. (And they make better dancers)
It’s virtually certain to be some sort of sexual selection. A more interesting question is why, in some societies, men fetishize large breasts, while others appear not to. Thus in some countries, women on average have rather large breasts and in others they tend to have small ones.
It is possible for sexual selection to get out of hand and even lead to extinction. Read about the Irish elk.
Sorry; you’re right. I was reducing the importance of more and more distant relatives, by the appropriate powers of 1/2. Yes, the father contributes one of the X chromosomes, which, presumably, governs female breast development.
Well, not quite. A very slight survival difference is enough to drive evolution. For example a 1/10,000 decrease in survivability will result in the trait being reduced to about a third of its initial incidence in 10,000 generations or perhaps 200k years in humans. And obviously, larger than necessary breasts are bad for posture, running and consume resources. Thus there must be some advantages for them, such as sexual selection via the handicap principle, and if they can also store fat in addition to be attractive to males, so much the better.
In a nutshell, women have large breasts not because they are easy, but because they are hard, and for the same reasons.
Agreeing here. Breasts are uniquely human, that is the large amount of fat covering mammary glands is unique. That means this characteristic hasn’t undergone the long term evolution of other human characteristics that are incrementally changed from our ancestors until reaching an equilibrium with function and survival.
I would dispute these suggestions. Breasts have a much greater range of sizes than the other body parts mentioned, even in women of the same overall size. You could have two women who are the same height and general build but one of them has breasts that are four times the size of the other’s. You’re not going to find two people like that where one of them has hands or ears that are four times the size of the other’s.