17
   

Why do girls have big boobs?

 
 
Reply Mon 19 Dec, 2011 11:15 am
My 10 year old son asked me this last night.

I started by explaining how female mammals nursed their young, reminding him of times we'd seen nursing infant mammals suckling and blahblahblah.

He pointed out that female cats and dogs don't have big boobs all the time -- only when they have babies and that if they don't have babies they never get big boobs.

That left me with explaining that maybe it was just a way to "advertise" their sexual maturity, but that really seems kind of a lame reason in the overall scheme of biology, especially since it is usually the male of a species that is more physically flamboyant.

So, biologically speaking, why do girls have big boobs?
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Type: Question • Score: 17 • Views: 6,711 • Replies: 61

 
DrewDad
 
  1  
Reply Mon 19 Dec, 2011 11:28 am
@boomerang,
http://en.wikipedia.org/wiki/Secondary_sex_characteristic
DrewDad
 
  1  
Reply Mon 19 Dec, 2011 11:29 am
@DrewDad,
I could not find a consensus on the exact evolutionary reason.
rosborne979
 
  1  
Reply Mon 19 Dec, 2011 11:30 am
@boomerang,
Boobs contain (are constructed) of a lot of fat. And relatively speaking, homo sapiens (especially US citizens) have higher body-fat than most other mammal species. Most other mammals have to run and hunt and fight (physically) to survive. If female dogs got to sit around (relatively speaking) and eat fatty food as much as most people do, they might have big boobs also. It makes you wonder what our ancestral females from 20k years ago looked like.

Then of course, there's the sexual selection factor in human evolution. Ancient statues seem to show a particular appreciation for "larger" women. This may have been because big boobs translated into fewer starving kids. As a result, 10yr old males are sufficiently aware of boobs to start asking questions about them. Smile

There may be multiple reasons why human females seem to have larger boobs than other mammals.
DrewDad
 
  1  
Reply Mon 19 Dec, 2011 11:32 am
@DrewDad,
Quote:
In females, breasts are a manifestation of higher levels of estrogen; estrogen also widens the pelvis and increases the amount of body fat in hips, thighs, buttocks, and breasts. Estrogen also induces growth of the uterus, proliferation of the endometrium, and menses.

I think this implies that breasts indicate higher fertility. Wider hips would be a survival characteristic prior to the advent of C-sections.
Mame
 
  2  
Reply Mon 19 Dec, 2011 11:38 am
@DrewDad,
From what I understand, wide hips have nothing to do with it. It's the size of the birth canal.
0 Replies
 
boomerang
 
  1  
Reply Mon 19 Dec, 2011 11:42 am
@DrewDad,
Yeah I get the whole hormonal thing -- that this is just what our bodies do but I'm really curious as to the why of it.

Secondary sex characteristics add a whole new layer to it. Why do so many men shave and so many women get boob implants? When you really think about it, doesn't it seem strange?

Wouldn't it make more sense if women just got big boobs when they needed them to feed their offspring?
0 Replies
 
boomerang
 
  1  
Reply Mon 19 Dec, 2011 11:48 am
@rosborne979,
I know a lot of skinny girls who have big boobs, though.

And I inherited a massive, fat cat that doesn't have noticeable boobs.

The sexual selection thing is what I was getting at when I tried to explain about how it advertises a female's sexual maturity. I totally get that most men like boobs and that maybe we've just evolved to have big boobs so we'll be selected as a mate. Maybe that's all there is to it.
Setanta
 
  1  
Reply Mon 19 Dec, 2011 11:55 am
Why do girls have big boobs?

Not all wimmins has big boobs . . . just the dumb ones . . . it's god's way of giving them a career opportunity . . . so there . . .
boomerang
 
  3  
Reply Mon 19 Dec, 2011 11:57 am
@Setanta,
Oh.... thanks!

Ya want I should make you a sammich now?
Setanta
 
  1  
Reply Mon 19 Dec, 2011 11:59 am
@boomerang,
If ya please . . . ya got cold meatload? Meatloaf are my favorite sammich . . .
0 Replies
 
DrewDad
 
  3  
Reply Mon 19 Dec, 2011 12:04 pm
@boomerang,
The problem is that a lot of our appearance is just completely random.

Chins have no function whatsoever. They're a physical characteristic that resulted from genetic drift.

Waterfowl have a bunch of vertebrae. You'd expect marine mammals to have the same thing, but mammals that are born with extra vertebrae end up with other birth defects because the genes are linked.
boomerang
 
  1  
Reply Mon 19 Dec, 2011 12:14 pm
@DrewDad,
Huh. Interesting.

I wonder what our bodies would look like if they'd evolved only in necessary ways.....
Setanta
 
  1  
Reply Mon 19 Dec, 2011 12:15 pm
Sheep have big boobs . . .

http://www.stocarstvo.com/saradnja/awassi_mediterranean_farm_repro_centre_files/Awassi_sheep_machine_udder_shape_Gan.JPG

Goats have big boobs . . .

http://img194.imageshack.us/img194/5826/alisabutt.jpg

Of course, cows have big boobs . . .

http://image.shutterstock.com/display_pic_with_logo/102209/102209,1217014406,15/stock-photo-cow-udders-full-of-milk-15345544.jpg

These are all animals which we have milked for thousands of years. It strongly suggests to me that big boobs are evidence of a selection bias. I suspect that wimmins with big boobs are the product of many generations of selection bias.
DrewDad
 
  3  
Reply Mon 19 Dec, 2011 12:17 pm
@boomerang,
boomerang wrote:
I wonder what our bodies would look like if they'd evolved only in necessary ways.....

Blue-green algae.
0 Replies
 
boomerang
 
  1  
Reply Mon 19 Dec, 2011 12:31 pm
@Setanta,
I'm not sure about that. We might need to round up Patiodog or Cow Doc to get a better answer but my quick Google search led me to this:

Quote:

Are baby cows born with udders?
In: Cattle Reproduction [Edit categories]


No. The udder develops during the time the heifer, after being bred at 15 months of age (breeding age), is pregnant with calf. The udder doesn't start developing until the third trimester, when it starts filling up with milk, and is ready until the calf is born and gets up and starts suckling.


Cows, sheep, goats, etc. might fall into the category of not getting big boobs until they need them.


Butrflynet
 
  4  
Reply Mon 19 Dec, 2011 12:35 pm
This is a cached version of this site. The original doesn't seem to be accessible. It is a very long article that lays out the current assumptions and theories and then counters them. Here are the assumptions and theories. I'll let you read the rest of the article to see how they are argued against.

“Are Women Evolutionary Sex Objects?: Why Women Have Breasts”

Excerpts:
Quote:
Since all mammals have breasts to nurse their young, it might seem odd to search the unique evolutionary past of humans for an explanation of their existence. Yet, there is a reason to do so. There is something different about human female breasts, leading scientists to develop theories about them: after the age of puberty, the breasts of a human female become “permanently enlarged,” although this is not the case in other primates, our closest evolutionary relatives.

If you were to look at a chimpanzee or a gorilla, or any other ape or monkey for that matter, the breasts of a non-pregnant, non-nursing female would not be enlarged. Although the breast tissue of a female ape or monkey swells when she is pregnant and nurses her young, once she is done lactating, it typically recedes back to a flattened form. Most of the time, you would not be able to distinguish a male from a female by the size and shape of breasts alone; breasts in non-human primates are not what scientists call “a sexually dimorphic trait,” one that exists in two different forms in the males and females of the same species.

Examples of sexually dimorphic traits in non-human primates include the large canine teeth of male, but not female, baboons, and the large size of male gorillas in comparison to females.

Darwin proposed that natural selection might not be the only evolutionary force at work. Instead, he claimed sexually dimorphic traits arose because the individuals who possessed them had an increased reproductive advantage stemming from another source: the advantage it conferred on them in terms of increased access to mates. Darwin argued that many sexually dimorphic traits were not advantageous to an individual in the struggle for survival but in the struggle over mating opportunities. Darwin called this differential access to mates “sexual selection,” and outlined how it worked in animals, including humans, in his book The Descent of Man (1871).

Darwin focused on two types of traits that increased access to mates: the weapons and other characteristics used and displayed by males when fighting among themselves over access to females, such as the large canines of baboons, and those traits that make males more attractive to females, such as peacock plumage. Interestingly, Darwin posited that females choose males, not that males choose females, suggesting sexual selection operated on males alone. This may be because he recognized that from a species standpoint, it makes good sense for all females to mate, while this may not be equally true of males: theoretically, it takes only one “good” male to impregnate a large number of females. Whatever the reasons for Darwin’s view that sexual selection did not directly modify females, it is clear he did not think that male choice among more or less desirable females was an important evolutionary force.

Yet, this is exactly what contemporary scientists argue in their attempts to explain the difference between the breast of humans and other primates. They claim that human female breasts became sexual signals to attract males. Females with this trait would have increased mating opportunities, thereby passing the genes for permanently enlarged breasts on to subsequent generations. A prime example of this way of thinking is the following statement by anthropologist, Bernard Campbell:

Since in the primates, and particularly among men, the choice of partners lies with the male, it follows that only the physical characteristics of the female are subject to sexual selection of this kind… breasts have always been attractive to men and have no doubt been subject to sexual selection (1970:304).

But why should this particular body trait have become the object of sexual desire?

Desmond Morris, a curator of mammals at the London Zoo, was among the first to offer an explanation. In his widely read book, The Naked Ape (1967), he suggested that permanently enlarged breasts in human females resulted from hominid bipedalism. It is widely believed among scientists that our earliest ancestors survived by becoming bipedal, that is, by walking on two feet in an erect position. Although there are a number of specific explanations for why this trait might have conferred an adaptive advantage on some ancient hominid population, scientists agree that bipedalism is the defining characteristic of the human species. Indeed, when a fossil primate is unearthed, the only sure way to determine whether it is a hominid is to figure out whether the individual in question walked upright.

The link between bipedalism and permanent breast enlargement, according to Morris, has to do with the erotic nature of breasts. He argues that as early humans (hominids) began walking upright, face-to-face encounters between the sexes became the norm, affecting the position used in sexual intercourse: males would no longer mount females from behind as they do among non-human primates. In the non-human primate position, presentation of the female buttocks to the male is an erotic display that stimulates male interest and excitement. With the advent of bipedalism, Morris argues, if females were to be successful in shifting male interest around to the front, evolution would have to do something to make the female frontal region more stimulating to males. This was accomplished, Morris says, through self-mimicry in which female breasts came to look like rounded buttocks: female breasts became mimics of “the ancient genital display of [the] hemispherical buttocks” (1967:75). Szalay and Costello (1991) have continued this line of thinking, but argue that permanently enlarged breasts sexually arouse males not because they look like buttocks, but because they mimic the appearance of female genitalia.

...

For sociobiologists and evolutionary psychologists, enlarged breasts are just another weapon in a female’s arsenal for attracting a man and keeping him around. For example, J. Cant (1981) suggests that breasts became signals alerting a male to which female would be more likely to raise his offspring successfully. Cant argues that females better able to build up fat and maintain it would have more reserves to convert to parental investment during pregnancy and lactation. Since breasts are primarily composed of fat, Cant argues that they became an indicator of the nutritional status of the female.

Roger Short (1976) also argues that females with shapely breasts were more likely to attract a male and keep him around, ensuring that he would take care of her and their offspring. Owen Lovejoy (1981) has come to a similar conclusion: he argues that females who could use the permanent features of her body to attract a male would have a distinct advantage over those women who relied on behavioral strategies alone.

These theorists stress how keeping a man around saved the human species from extinction. Short, for instance, argues that females became dependent on males for food in the far reaches of the human evolutionary past because females became restricted in their movements due to the increased dependency of infants on her care. Unable to support herself and her children alone, a woman would need male parental investment in children became increasingly necessary for survival. According to him, breasts became objects of attraction that ensured the pair bonding between a male and a female, and thus the survival of children.

Lovejoy not only focuses on the role male provisioning of dependent females played in the development of permanent breast enlargement, he also puts it at the very center of his explanation of bipedalism and the evolution of humans. Cant thinks bipedalism arose to solve what he calls “the demographic dilemma of apes.” This dilemma resulted from the reproductive strategy used by apes, one referred to as K-selec­tion. As paleoanthropologist, Donald Johanson and science writer, Maitland Edey explain:

There are two fundamentally different ways in which an animal can function sexually: It can produce a great many eggs with an invest­ment of very little energy in any one egg, or it can produce very few eggs with a large investment in each. These are known as the “r” strategy and the “K” strategy respectively . . . “K” is obviously far more efficient than “r,” but it too has its limits. Accidents, predation, seasonal food failure, illness-all take their toll on animals. Losing an infant to one of these hazards after an investment of five or six years is hideously costly compared with the loss of an egg by [an r strategy animal]. (1981:46)
sozobe
 
  3  
Reply Mon 19 Dec, 2011 12:37 pm
@boomerang,
It's an interesting question.

A few thoughts... first, the "hourglass figure" (boobs, but then in at the waist, then out at the hips) has a high correlation with fertility. Hormones, adequate fat stores, health (tummy fat is associated with lower health than a flat tummy but fat elsewhere), lots of different things.

So because of that correlation, the hourglass figure and its components (the bigger boobs, the bigger butt, the smaller waist) become sexualized -- 'cause men "want" (at an evolutionary level) their sperm to result in as many healthy babies as possible.

Not all women do have big boobs, and they're the ones who you can see the most change (like the doggies) when they're lactating. So that does happen with women.

All women's boobs get bigGER when they're lactating -- if they were small to start with it's more noticeable than if they were big to start with, but there's always some change.

Meanwhile DrewDad makes an excellent point about not everything having a purpose per se. Male nipples (on all mammals, not just humans) are another example there.
Setanta
 
  1  
Reply Mon 19 Dec, 2011 12:37 pm
@boomerang,
Yeah, but they keep them whether they nurse or not, and they keep them after nursing. Human wimmins don't get boobs until they reach reproductive age, you know.
0 Replies
 
Setanta
 
  1  
Reply Mon 19 Dec, 2011 12:40 pm
There is something seriously weird going on here. I suddenly got some strange music going on, and looked all over the computer to try to identify the source--but i couldn't find the source. However, when i closed the window for A2K here, it stopped. Maybe something from one of the links in this thread?
 

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