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Is there an evolutionary or other reason that men get bald but women don't?

  1. Jul 19, 2009 #1
    I'm not looking for any causal explanations, i.e. "men stop making testosteron which causes baldness". I'm not saying this is the case - just so you know what i mean. But is there a reason evolutionary reason, or anything similar, that men lose their hair whereas women don't?
     
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  3. Jul 19, 2009 #2
    1. Men choose a mate that will likely bare young well and be around to raise them. So youth and health are the top priorities. Lots of hair indicates lack of disease and indicates youth, generally.

    2. Women choose their mate to protect and provide, which means a bit older is OK as long as he is somewhat smart and rich. In fact there might even be some minor affect in which baldness indicates age, and age is somewhat of a good thing because it indicates his ability to survive and remain healthy. Baldness also indicates the presence of at least some testosterone--which is also a good thing because he'll be more willing to fight, etc..
     
  4. Jul 19, 2009 #3

    tiny-tim

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    I don't think there can be an evolutionary reason …

    suppose a mutated gene caused a woman to go bald aged, say 50 …

    that wouldn't affect her suitability as a mate, and therefore her number of children, so there would be no reason for the gene to be selected against.
     
  5. Jul 19, 2009 #4
    True... in fact, back when evolution was happening in humans the way it does in the animal kingdom, i'm not sure if even half of the males lived long enough to see their head turn into a shiny pool ball.

    I guess it's just a curiousity, if not a coincidence? Some males do go bald in their 20's or 30's, though, i can imagine a female being bald by that age having some consequences for their reproductive abilities.... still, especially in primitive times, i suppose they mate before that.
     
  6. Jul 19, 2009 #5
    Yes, people have a tendency (especially evolutionary biologists which always surprised me) of assuming every trait a species has was a result of natural selection. However, if something is not directly selected AGAINST then any mutation can thrive regardless of its usefulness just through a fluke. Plus, even traits that would be selected against have a certain probability of surviving the test of time
     
  7. Jul 20, 2009 #6

    jim mcnamara

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    We-ell, first off - women can and do go bald. The frequency of female baldness in a population is simply far less than for men.

    Pattern baldness may be very evident in individuals by the time he/she reaches the early 20's, sometimes even late teens. Male or female.

    The age of onset of menses controls fecundity in a population. In the US in 1900 the average age of the onset of menses was 18, although it is now considerably lower. Primarily due to improved nutrition. So it seems somewhat unlikely that women of reproductive age - say 18+ - were completely unaware of baldness when selecting a potential mate of a similar age. There are many other much more important factors in mate selection, despite what you see on TV.

    I dunno if this is a word : culturo-centric. But I think your perceptions of baldness are guided by Western culture's vanity problem. If this was 20000 ya and a bald guy brought home more meat than another guy, I'm sure any woman would prefer eating + bald mate over semi-starvation + non-bald mate. As someone else mentioned above using income rather than hunting prowess.

    YMMV.
     
  8. Jul 23, 2009 #7

    Moonbear

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    Baldness in females is usually a symptom of excess androgen production, which is also associated with a decrease in fertility (whether it's a cause or effect depends on the specific reason for the androgen excess). So, evolutionary history could be involved here, since women who are bald (or doomed to become bald) would also have difficulty getting pregnant. Conversely, male-pattern baldness in men is associated with androgen production and may be associated with a longer period of time during which they remain maximally fertile and can continue to sire more offspring in their lifetime.
     
  9. Aug 4, 2009 #8
    Male pattern baldness makes a face look larger and more masculine which can present a more intimidating look and scare off potential competitors. The effect is the opposite of bangs which make your face look smaller, younger, and more feminine.

    Baldness, however, can cause a significant loss of body heat through the head which is not a big deal nowadays but probably used to be a big negative factor.

    Men and women also have age related hair loss where cells including hair follicle cells just become less efficient as the get older.
     

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  10. Aug 5, 2009 #9
    You don't think that bald woman would be sexually selected against? I don't know about 50,000 years ago, but men are some pretty superficial beings, and currently it would not be far fetched to say that bald women are less sought after than those who aren't.
     
  11. Aug 5, 2009 #10

    tiny-tim

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    I don't think that bald woman aged 50 would be sexually selected against. :smile:
     
  12. Aug 5, 2009 #11
    Would you marry a woman who's 50 yo mother was bald? Well, not you in particular, but my point is mate selection probbaly included judgments on relatives even in millenia past. Also a woman that goes prematurely bald, even after menopause, would probably lessen the chances of here offspring's survival because its less likely a man would be around.
     
  13. Aug 5, 2009 #12

    tiny-tim

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    Marry? What's "marry"?

    I'd drag her off to my cave, give her plenty of children, and maybe trade her in if I got fed up with her.

    Why would I bother about her mother? :confused:
     
  14. Aug 5, 2009 #13
    Baldness is autosomal recessive. Its one of those cool sex linked genes. For some reason women need both recessives to go bald, but men only need one. As a result men are 3x more likely to experience pattern baldness. My professor used this as her example for explaining sex linked genes. I know you didnt request a reason, but I thought a little explanation as to why men go bald more than women would help. As for evolution, I find a lot of people talk about evolution as though its a consciously planned thing. It hard to remember that it depends on random mutations. Its always possible that certain mutations are lethal, and so some things are unavoidable. Its also important to note the very long time frame of evolution.
    As a side note, some women are really attracted to bald men. My mother cant wait for my dad to go bald, its really strange, but Ive heard of other women who find it attractive as well.
     
  15. Aug 5, 2009 #14
    Ah, missed that :shy:
     
  16. Aug 16, 2009 #15
    I think the most logical explanation for this comes from theories of senescense. Male baldness, originally a fluke mutation in some regulatory gene, is genetically inherited and comes about as a consequence of aging. Now, because this trait usually doesn't appear in an individual until AFTER he has reproduced or (at least) selected a mate, as would have been very likely in ancestral human populations given a much shorter life expectancy, then natural selection can no longer act on this trait because the genes for it have already secured a place in the next generation. Basically, any trait that shows up after the organism has reproduced is invisible to natural selection. Note: this is an over simplification and there are many ways for parents (and their post-reproductive phenotypes) to influence selection on their offspring. However, I would argue that in humans these effects are mainly behavioural and focused on parental care. The offspring of a bald, supportive father will certainly do better than one that has run off with a full head of hair.

    Despite all of this, there probably never was a very strong selection pressure on this trait. To quote Jim:
     
  17. Aug 16, 2009 #16

    arildno

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    Bald heads are sun light attractors, and since men retain physical strength into their granddad years, this can readily be explained as the "gramps factor":

    By guarding/accompanying their grand-children, grand-fathers also attract most of the sunlight to their bald pate, so that the younglings do not evolve sunburns etc.

    Thus, we have a simple evolutionary cause for why middle-aged males become bald. :smile:
     
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