basically like. why do women just have breasts all the time when to my knowledge the only purpose of them is to feed children. why don’t they go away like other mammals’ when you haven’t had a child.
In: Biology
Probably sexual selection.
Plenty of mammals – and non-mammals for that matter – have secondary sexual characteristics that serve no known purpose except to attract the opposite sex.
It makes perfect sense that our switch to walking upright could’ve coincided with the development of such secondary characteristics closer to our new eye-level than whatever was there before.
The theory is due to our relatively higher ovulation cycle compared to other primates, the constant presence of breasts may have developed as an evolutionary advantage to signal fertility to potential mates. The fact that humans ovulate year-round when other primates tend to only ovulate once a year during optimal seasons such as spring or summer, can be seen as an evolutionary advantage we have over our other primate cousins.
This is also probably why women’s butts are constantly big, which is another trait that usually only happens when a female primate is ovulating. For baboons and chimpanzees I think, the female’s butt will swell and turn a bright red, which instinctively draws a male’s attention.
We walk upright, so we present ourselves differently, and different parts of our bodies are more visible to each other than with animals that walk on all fours.
This has led to us noticing and finding attractive parts that wouldn’t otherwise be on display, like chests and abs.
Suppose you’re looking for a woman to be the mother of your children. You know what children eat and where it comes from. You’ll probably figure that a woman with more going on there looks more capable of sustaining your eventual children. So that trait becomes an advantage in finding a mate and will be passed on to your female descendants.
Attraction and limited resources.
Breasts are a fertility indicator. Males recognize that, so females with noticeable breasts have a reproductive advantage.
Pregnancy is extremely taxing on the body. On top of the gradual development of a baby, the female body is already undergoing significant changes with the abdomen, hips, pelvis, and breasts. It’s a huge amount of change without adding in full breast development. It’s common to need to take vitamins and supplements just to not end up deficient in a swathe of nutrients already. It might just be too taxing on the body to form breasts exclusively during pregnancy (or at least too taxing to be favourable).
Edit: Several have already pointed it out, but fertility indicator as in a broad sign of both health and sexual maturity. Particularly given the context of food insecurity experienced for much of our pre-history, having the means to acquire enough calories to support the development of larger breasts points to much greater chance of surviving offspring.
Almost everyone in this thread is leaning hard into ‘breasts evolved because I like breasts’ – evolution doesn’t work like that. It doesn’t always make rational ‘decisions’ – but if pregnancy is a time of enormous resource strain put on a woman’s body (which it is), it certainly would seem an odd time to make non-essential body changes when those could happen another time. In addition, breast growth is controlled by some of the same hormones that kick off other aspects of puberty, so delaying that would arguably need a more complex hormonal system. Easier to just get it all done at once. “While we’re building the extension let’s redecorate and put a new floor in too”
I can’t even begin to imagine how many newborns would enter the world every day if women only had boobs when they are pregnant lol.
Your error is to believe that sex is for reproduction only.
There are two reasons for sex: bonding socially with one or more partners and reproduction. Most mammals focus on the latter, but many big mammals have both, which is called recreational sex. When sexual selection begins to act is to select features that increase your chances of reproduction, but recreational sex also increases your chances of reproduction, so species evolve more diverse forms of making animals interested in sex in general in the same way that they evolve stronger and longer bonds with their offspring.
That’s why we are attracted to big round boobs, long hair, thick thighs or round hips and women are attracted to beards, chest, arms, abs or hips for sex, despite none of those body parts having reproductive roles.
There’s a theory that prominent breasts, lower sexual dimorphism, smaller canines, upright posture and handedness co-evolved. Breasts signal that females are infertile, so less guarded by alpha males. Susceptible to approaches by smaller lower ranking males with gifts (sex for beatles). Bipedalism and handedness makes carrying gifts easier, being smaller is less of a threat and being less aggressive is attractive to females. In short, the nerds found ways to attract the females, who found ways to evade alpha male attention and preferred the nerds.
The short answer is because men like them. Other apes don’t have breasts like humans do, and the reason why is because they attract mates in a different way. Female chimps signal sexual receptivity with a genital swelling, which is very easy to see. Chimps are knuckle walkers and don’t need the large gluteal muscles that humans have for upright walking. As humans evolved to walk upright, the sexual signals our ancestors used became less effective, so they were lost and new ones evolved in their place. Permanently swollen breasts are a sign that a woman is sexually mature and serve as an advertisement to men
Large breasts and wide hips generally indicate that a woman’s body is healthy for child bearing. Therefore, evolution can favour that men are more attracted to those features (or conversely, in populations where men favoured small hips and small breasts, infants might have slightly higher infant mortality and therefore have evolution pressure against these). Therefore humans evolved to prominently display these features.
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