Sexual Selection

     Many people have never heard of Charles Darwin's theory of Sexual Selection, even though it has played an equally important role in survival of many species, including humans, as his more well known theory of Natural Selection. Like Natural Selection, Sexual Selection is less of a theory then it is a common truth that it is widely accepted among all verities of biologists today. In this article I am going to look into what Sexual Selection means and how it works. I am going to give some examples of it in the natural world, some examples in humans, and look into how it influences a specie's  evolutionary development.
     So at this point you may be asking, what is Sexual Selection?  "Sexual selection is a special case of natural selection. Sexual selection acts on an organism's ability to obtain (often by any means necessary!) or successfully copulate with a mate." (-evolution.berkeley.edu) Charles Darwin defined Sexual Selection as: "sexual selection depends on the success of certain individuals over others of the same sex, in relation to the propagation of the species. It is a struggle between individuals of one sex, generally the males, for the possession of the other sex."

     Sexual Selection comes in many forms. Often times there are adaptations that species have acquired that at first glace give no advantage to that specie's survival. In fact in many cases, these evolved traits appear to do the opposite, in that they seem to put the species at more risk of not surviving. Take for example the male Peacock's large multicolored tail feathers. These large brightly colored feathers give absolutely no advantage to the Peacock's survival. The feathers actually make them much more visible to predators and thus less able to hide then their female counter parts. And the energy that goes into growing those extravagant tale feathers could have instead gone into making the bird stronger or faster, which in-turn would have allowed it to have an advantage over other birds. The only purpose to the Peacock's big bright feathers is to help it advertise to females that he is a good mate. This allowed the Peacock with the largest, most pronounced feathers to be the most successful at passing on his genes. This is a classic example of Sexual Selection in it's purest form, and similar examples can be found all through the natural world. Females and males form preferences for extravagant physical ornaments. Over time these preferences create directional selection for the species. The chosen males or females will out-reproduce the un-chosen male/female.
     More examples of this theory can be seen in animals such as Deer, Mountain Goats, Bulls, and Walruses, where the males of the species have large tusks or horns. These mammals use their tusks/horns to fight each other as a form of competition for mating rights with the females of a group. A male with large strong tusks has the potential to win the fight with another male, which enables him to mate and pass on his genes. (genes which among other things, contain the potential of having large tusks.) Over time this results in a directional selection for males with large tusks.

     It is theorized that Sexual Selection's purpose is to continue the 'best' genealogy. ( 'Best' meaning: most adaptable to change, most adapted to the environment) Mates look for signs that indicate that their potential mate will be able to either/or, provide good support in raising the young, produce healthy strong off-spring, will be fertile. This in-turn helps the species to continue to survive and evolve into the future. "The advantages of discriminating mate choice by females were examined by Maynard Smith's (1956) experiments with drosophila mating behavior. He was able to demonstrate that (1) females choose certain genotypes over others, and that (2) the choice tended to be adaptive for those females." (-missouri.edu -Sexual Selection lectures)

     Just as it has to many other species, Sexual Selection has played a significant role in the evolution and history of propagation of the human race. For example: "Unlike other apes, human females’ breasts develop before first pregnancy and are permanently enlarged." (-Human Evolution Journal, May, 1987)It is suggested that the large human breasts act as a way to attract males, or that they help to hide females' reproductive condition.
     Another example of sexual selection in the human species is that people are relatively hairlessness compared to the other great apes. This is part of the physiological resemblance between adult humans and adolescent chimpanzees. This makes adult humans look generally younger. The human youthful appearance has evolved because males prefer young looking mates because a young female has a much higher chance of surviving a pregnancy.
     You may have noticed that you have certain likes and dislikes about physical characteristics when you choose a sexual partner. There are certain features that you find attractive but for some reason your best friend is attracted to very different physical features then you. It is quite possible that Sexual Selection has a lot to do with this. Every person carries a slightly different set of genes. And within those genes are evolutionary traits that you have inherited from your ancestors. Since Sexual Selection has played a critical role in choosing those genes you carry, it is very possible that they are also playing a major role in the types of characteristics you are attracted to. Think about it... If you are attracted to thin people this may be because a thin person has much less calorie requirements thus meaning that they would be able to spend less time providing for themselves and more time providing for their young. Or lets say you are attracted to heavier people. This could be because a larger heavier person may be able to provide more protection for his/her young and a heavy person must already be successful at gathering resources to be heavy in the first place. Then there are things like different color hair and eyes. These may simply be ornaments that were meant to attract mates, much like the male peacock's bright tale feathers. So far there hasn't been any solid Natural Selection based theories as to why humans have different color hair, eyes, or even skin. Research shows that differences in physical coloration have no survival advantage. This is also true for variants in shapes of physical traits such as, eyes, nose, ears, faces, breasts, vaginas, and penises.(-To read more about this: The Third Chimpanzee)

     Sex has played an important role in the development of our many cultures and has ultimately done the same for the development of our civilization. We first need to have an understanding of Sexual Selection in order to understand ourselves. It has played a significant role in our development as a successful species. Sexual Selection is not something that can be over-looked.

Sources:

www.stanford.edu -Sexual Selection Essay

evolution.berkeley.edu

"The Third Chimpanzee" -Jared Diamond

web.missouri.edu -Sexual Selection lectures

"The Descent of Man, and Selection in Relation to Sex" -Charles Darwin

"Evolution and the Theory of Games" -John Maynard Smith

"Human Evolution Journal"