last night I was up until 1 am writing an essay for a professor.
Don’t worry, it wasn’t a required essay. It was just for fun, stemming from a discussion in class. Yes, this is telling, I had plenty of homework, NaNoWriMo, chores…and I went of on a wild tangent. Educational as it was, it was not required. The only benefit was from me learning stuff. I thought I was cool & smart & stuff…
Anyway, I’m curious, how can I make it better?
The professor’s response is in the below. Sources in extended entry
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Why do humans have so little hair?
The other day in class our instructor brought up the idea that humans may have lost most of their body hair due to female choice. I asked, “Historically speaking, how much choice did females have?” From the class reaction, for a moment a felt a bit like Larry Summers, (who infamously suggested that it might be innate ability or innate preference that leads to more men than women in science).
Our professor quickly pointed out that in many bird species it is the female that chooses the showy male bird. I countered with elk, and the big bull gets the harem. We quickly agreed to limit the discussion of female choice to primates.
The professor said that it seems to be in primates, the more closely the males and females are in size the less likely it is for the male to have a harem. Judson agrees, pointing out that “In monogamous species, males and females tend to be roughly the same size…human males tend to be only slightly bigger than females, and there is considerable overlap, with some women bigger than some men” (Judson, pg. 162). Next our professor, and also Judson, pointed out the correlation between relative testicle size and monogamy, “
Next, consider physical differences between human males and other male apes. As you know, testicle size is usually associated with the risk of sperm competition. Males that are at low risk of sperm competition – either because they are good at defending their harem or because they are paired with a faithful female – generally have testicles that are small in relation to their body size. Males that are at high risk of sperm competition-either because they pursue a strategy of seducing the partners of other males or because most females mate promiscuously-generally have enormous testicles in relation to their body size… [gorillas having small testes, while chimpanzees having large testes]…human males have medium-sized testicles, suggesting a low to moderate risk of sperm competition. This fact, plus the relatively small size difference between men and women, is exactly what would be predicted for a mostly monogamous species.” (Judson pg. 163)
In an attempt to clarify my question, and the reasons for asking it, I present the following.
Through out human history there have been wars, and many times the women were treated as simply spoils of war. Using the Bible a historical social commentary, when the Isrealites attacked a city, if it did not surrender, when it fell “the women, the children, the livestock and everything else in the city, you may take these as plunder for yourselves” (Deut 20:10 – 14). This tradition was continued in medieval Europe, and “the women of a besieged town taken by storm might be raped” (Morrow, pg 378).
The Japanese soldiers raped thousands of Chinese women during the occupation of Nanking during World War Two (Morrow, pg 378)
This happened in the early 1990s in Europe, during the wars following the breakup of Yugoslavia. “Moslem and Croat women from many parts of Bosnia were herded into schools and warehouses and raped repeatedly….kept in these camps for several weeks….Those able to bear children were almost all impregnated” (Glenny, pg 209). It is currently happening in Dafur (the Economist, 13 Oct 2005, 9 Feb 06).
Anthropologist Napoleon Changnon, who was one of the first to study the Yąnomamö people of the Amazon noted that they “regard fights over women as the primary causes of their wars…Although few raids are initiated solely with the intention of capturing women, this is always a desired side benefit” (Changon pg 123).
The above examples show that through out history, especially during the case of a fight between two groups of men, the winners get to keep the females. Which shows why I used the analogy of the bull elk and his harem. Although, the above examples show that a group of men can capture a group of women, possibly for procreation. When captured during a fight between two groups of men, which happens more than we like to admit, we can assume that women do not have the option of choosing the less hairy rapist.
Is it humans that are the only species that fights for females? Doubtful, because for “males in many species, females are the limiting resource for reproductive success” (Wilson, pg 377). Bands of chimpanzees have been shown to attack other groups of chimpanzees and the “results indicate that males are largely successful in defending their females from outside males” (Wilson, pg 377).
But are there times, perhaps when there is peace and plenty and the female has a choice between suitors? Certainly, it is one of the hallmarks of civilization. But I am more concerned with our evolutionary history, and that will have to deal with time before civilization. Perhaps there were no wars, because there were not enough people to form tribes.
Once again to the Bible there is the story of Ruth, who actually chose who she wanted to marry. The Bible does not mention if he was hairy, only that he was a land owner.
It is true that men and women “discriminate on the desirability of potential mates, partly on the basis of physical qualities” (Gangestad, pg 531). But evolutionary psychologist Geoffrey Miller says “Looks are important, but only for the first five minutes’. …Miller’s studies suggest that a man’s sense of humor, and his musical or artistic ability – traits that typically do not bring material advantages – seem to be valued by women as indicators of high intelligence and creativity.” (Anderson, pg 33).
A better indicator for mate preference than looks might be smell. In the classic smelly t-shirt experiment, men and women wore t-shirt to bed, and the next day people were asked to pick the t-shirt that smelled the best (Anderson pg 32). Consistently people “prefer the smells of those whose genes at [the MHC] complex are different from their own” (Judson, pg 52). The major histo-compatibility complex (MHC) is “most variable region of the human genome and plays an important role in immune function” (Anderson, pg 32). This area seems to give each person a unique odor, and “spontaneous abortions are more likely when couples match at particular MHC genes” (Judson, pg 52).
So why is there a lack of hair on humans compared to other primates?
“A recently mooted hypothesis that human hairlessness evolved late in human evolution as a result of the adoption of clothing and the need to reduce the load of external parasites finds no support in light of the overwhelming evidence of the importance of hairlessness in thermal sweating and whole-body cooling in maintaining stable core temperature and homeostasis.” (Jablonski, pg 599).
(The Plague showed that external parasites could prove harmful to clothed modern humans.)
Of the primates, humans have the highest ratio of eccrine sweat glands to apocrine sweat glands (Hanna, pg 272). The eccrine sweat glands are used for thermoregulation, secreting mostly water (Martini, pg 168). The apocrine sweat glands produce an oily, potentially odorous, secretion (Martini, pg 167). Maintaining a homeostatic body temperature is important for creatures that depend so much upon their brains. Less body hair helps thermal regulation in a hot environment “because it increases thermal conductance and permits additional heat loss through sweating” (Jablonski, pg 598-599). Studies have shown that “humans …the highest capacity for heat loss through evaporation of perspiration exceeding that of monkeys [macaques and baboons] by a significant amount…. on the basis of the anatomical distribution of eccrine glands, these primates [great apes] also seem inferior to humans in sweat capacity” (Hanna, pg 260.)
I do openly admit that many times it is the female that chooses the male, especially in our current society. But when society is lacking, since on average “it is undisputed that men have greater physical strength than women” (Quinn pg186), there are many cases when females do not have the option of picking the less hairy man. The better explanation is that humans are less hair so they can sweat to beat the heat.
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But GBatT,
How come other apes and chimpanzees, which evolved in equally hot, humid environments have also not become somewhat hairless? Why haven’t ALL species in hot humid environments evolved hairlessness?????
Furthermore, you are not going back far enough in time to surmize a hypothesis. The examples you quote for human male bravado over female ‘weakness’ were from historical dates of maybe 2-3,000 years ago. Humans evolved from chimps and apes over 5 million years ago!!!! None of your references adequately address this discrepancy. Finally, I hate to be a stickler, but none of your references are experts in evolutionary biology…I am not swayed.
-Professor
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