Nostalgic Moment 04/30/2012

Remember when we only had to worry about which sugar cereal would best complement the Saturday morning cartoons? Remember when there was no such thing as organic cereal? Remember when cartoons were actually good?
I do.

Maybe Physical Appearance Does Matter...

[This particular essay is pretty long so I’m going to put the moral of the story at the beginning. Here I argue that we find it important to define attractiveness because it is—naturally—the greatest indicator of the ability to bear physically healthy children.]

 The dynamics of a nightclub are always entertaining to me. I normally try to stay away from true clubs (as in electronic music playing so loud that ones’ thoughts are lost in the 808s—not to mention what the alcohol does to peoples’ thoughts) but recently I was talked into going. As always, my friend and I were discussing if he would talk to a particular girl in attendance that night. As always, he was quick to dismiss anyone that I pointed out. This made me think; how do we define facial attractiveness? Half of the girls that I pointed out were decent—at least facially—in my opinion. Maybe I’m just not that picky. But to my friend, many were not even worth consideration. Aside from the question of  how we define attractiveness, why do we even find it important to define attractiveness?  

I was curious to find out some of the answers that would be proposed for the questions that I put forth so I asked my mother. She told me (while drooling over the phone) that she defines attractiveness as a 6’5”, dark man with a bald head and a muscular build. Not very helpful.  I then went on to ask a different female friend. She admitted that she did not actually know why she considered some people attractive and others not so much.

The theory of sexual selection may serve as the underlying theory as to why not just humans, but rather many species find it important to define beauty.  Ronald Fisher, who set out to explain natural selection is his book titled The Genetical Theory of Natural Selection stated that “ the existence of sexual preference is to be ascribed to sexual selection are 1) the existence of sexual preference at least in one sex and 2) bionomic conditions in which such preference shall confer a reproductive advantage” Simply put, there must be a reason for one sex to be choosy which will in turn allow for the greatest number of offspring which will in turn survive to breed even more offspring.  Thus, species find it important to define attractiveness, in its most elementary form, because doing so will allow them to mate with those which will give the offspring the opportunity to survive to reproducing age. In other words, attractive individuals appear to bear more fit genes.

Grammer and Thornhill (1994) conducted a study to infer the relationship between facial attractiveness and sexual selection in humans. They refer to sexual selection according to the parasite theory, which states that individuals are likely to choose mates based on characteristics that confer resistance to parasites: “The parasite theory proposes that beauty of bodily form is perceived as a cue to high parasite resistance by animals in choosing mates.” Thus, the offspring of the chosen individuals will have the greatest fitness.  Studies prior to the one conducted by Grammy and Thornhill concluded that secondary sexual traits are positively correlated with the quality of the immune system.  This is especially true in human males. As noted, “only healthy organisms can afford the high testosterone handicap on the immune system that is necessary for the production of elaborate sexual traits“ (as qtd. by Grammer & Thornhill).  High levels of testosterone at puberty influences secondary sex characteristics such as the facial features of enlarged jaws, chins and cheekbones. This caused Grammer and Thornhill to hypothesize that such features would be considered attractive by women.

On the other hand, heterozygosity (possessing one dominant and one recessive version on a specific gene) also confers immune function; this correlates positively with parasite resistance. Individuals heterozygous for MHC genes display greater ability to mount an immune response to a wider range of antigens. Contrary to secondary sex traits, which increase in intensity as sex hormones increase during puberty, heterozygosity results with average trait expression. In other words, heterozygosity correlates positively with average trait expression.  Therefore the scientists hypothesized that average facial traits in women would be considered attractive by males.

To test the hypothesis, the scientists allowed participants to rank both computer generated faces in order to create faces with average facial dimensions and structures and faces with extreme facial dimensions and structures. As hypothesized, women found the males to be attractive when the features were extreme and males found the women to be attractive when the features were average.  These findings imply that, though one may find it difficult to define what an attractive face looks like, they somehow have the ability to define an attractive face that simultaneously corresponds to a healthy face that will give rise to healthy children.

I chose to begin my discussion concerning sexual selection with a human example because it is naturally easier to relate to humans. I must concede, however, and admit that some problems arise when conducting studies such as these in humans. The first one that comes to my mind is the influence of modern media in humans’ evaluation of attractiveness of individuals. Also, there are other characteristics, which may influence humans’ discretion. There is nothing inherently healthy-seeming about my mom’s preference in dark, 6’5 black men with an athletic build (possibly it’s the fact that this type of man may be able to rescue her from a burning house? My point is that there are a million ad hoc explanations that one could generate for any physical characteristic). Nevertheless, due many external influences, my mom finds this class of males attractive. Fortunately, there are many other examples of sexual selection in nature. One such example is the African long-tailed widow bird (which I will refer to as simply widows), as discussed by Richard Dawkins in The Blind Watchmaker.

In widows, females have the luxury of choosing which males they will mate with. Males that are able to attract mates are usually very successful to the point where one male may attract multiple mates. As explained by Dawkins: “This means that here is a surplus of males in one population who do not reproduce. This, in turn, means that females have no difficulty in finding mates, and are in a position to be choosy.” What gives the male birds the ability females? The answer lies in their exaggerated tail feathers. Male widows with longer tails more often then not win the hearts of female widows (the length of the tail has a functional limit due to the fact that it is burdensome to carry and makes the males prone to predation; I elect not discuss the relationship of sexual selection and natural selection in this essay).

This leads us to an important question, why are long tails preferred? Dawkins explains that the answer lies within the widow genome: “Female preference is a quantitative variable, and we can assume that it is under the control of polygenes in just the same kind of way as male tail length itself.” It is important to note that the genes for male preference, as well as the genes for tail length, are not sexist. That is to say that they do not discriminate based on sex— although extraordinary tail length may only be expressed in males, the genes remain in women as well. Likewise, preference is not undertaken in males but still exists. This is an essential to our understanding of sexual selection because we now are able to establish the fact that tail length, as well as preference for tail length, is something that is passed on from generation to generation together. Dawkins explains that the preference for long tails specifically could have arisen by chance: “the moment a majority, however slight, started to accrue among females for one type of preference rather than the other, that majority would be reinforced in subsequent generations.” In this way, since preference and tail length are inherited together, there will be a population wide preference for long tails that will only intensify over time (once again, I must note that there exists a functional limit).

As we have seen, sexual selection may allow one specific sex to infer which mates are most suitable for rearing fit offspring. In considering the benefits that species may receive in carefully choosing a mate based off of physical characteristics, I was lead to investigate why this type of behavior is not employed by more species. I came across M. Bastocks’ and a study in 1956 conducted on Drosophila melanogaster or fruit flies. In order to study sexual selection, Bastock mutated genes that determine the color of the body of the flies. He then observed the mutated flies behavior and ability to attract a mate. In an earlier study conducted by C. Petit in 1954, flies were randomly mutated via x-ray treatment and also observed the flies’ sexual activity. Together, they observed that the flies with mutated body color tried much harder to attract a mate and were often unsuccessful in their attempts. On the other hand, flies lacking genes vital to their physiology did not have trouble attracting a mate. However, overtime these flies were selected against due to pleiotropic effects caused by the mutations—phenotypes that arose via indirect interaction of the gene in question were unfavorably looked upon.

Upon further reflection, these results actually make a lot of sense. Hypothetically speaking, let’s say I spotted a woman with a blue face at my favorite bar. Call me crazy, but my first reaction wouldn’t be, “Wow, she would be the perfect mother for my children!” Rather, my response would most likely be along the lines of, “RUN!!!” Or, at the very least, she would have a lot of explaining to do before I consider even giving her my number, not to mention the possibility of a relationship. On the other hand, let’s say I spotted a woman that looked like Halle Berry’s sister at a bar. Unfortunately, she has sickle cell anemia. My first reaction wouldn’t be, “I feel like she has a very serious physiological ailment.” My first reaction would probably be, “get her phone number!”  But, after generations of offspring with sickle cell anemia, traits that may be associated with sickle cell anemia will soon be looked at with caution; my friends’ children would know to not touch a woman that looks like Halle Berry for fear of sickle cell anemia.

I admit that my example is an exaggeration. In principle, however, the same phenomenon is occurring in the studied flies. Although they may not be selecting mates based on a particular physical trait, they have an ability to select against traits that are abnormal, which have a higher probability of birthing unfit offspring—sexual selection!

But why is sexual selection so profound in some species and not others? Consider fruit flies for a moment; it is possible that a couple of the body color mutants (by chance) attract a mate and (by chance) give rise to offspring with increased fitness. In other words, these random combinations happen to bear super fruit flies! Not only would the majority of flies within the population tend to shift in color due to their increased fitness, but women preference would also shift away from the standard color of gray to the new color, as discussed earlier. As Bastock put it, “Although [the mutation’s] effect is deleterious to mating success nevertheless it could be incidentally incorporated in an isolated population if the mutant concerned were useful in any other sense” (as qtd. By Claudine Petit and Lee Ehrman) Thus, although many species may not have elaborate advertisements in their quest to attract a mate, one could argue that sexual selection is a theory that can be applied to all species that have two separate and distinct sexes.

As I have shown, the effects of sexual selection can play a large role in the evolution of many species where there are two distinct species and at least one has the luxury of choosing a mate. Even more, the sexual selection that occurs my have important consequences on the success of future generations. In species where there is no need for one sex to be choosy, specific behaviors and characteristics may not need to evolve, thus a specific display of sexual selection may not be observed. According to Grammer and Thornhill, humans are an example of a species that employs sexual selection.

The next time your friend tells you that you worry too much about the physical appearance of your significant other, blame evolution.

Welcome

Hello World,

Please follow a young man on his journey to find out where he belongs in the larger scheme of this thing we call life. On this journey, I will be writing short essays and anything else aimed at describing the world around us. Simultaneously, I will take time out to reflect on the simpler joys in life that we all-too-often fail to acknowledge due to our excessive self-absorption. Thanks for stopping by and as always... enjoy!

--Mr. Green