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Major points on faces where symmetry/asymmetry can be noticed

Major points on faces where symmetry/asymmetry can be noticed

Selecting a mate is one of the most critical moments in the life of any creature, whether human or animal.  In order to successfully produce offspring that will continue to pass on useful genetic traits, one must choose wisely.  There are multiple factors that contribute to the selection of a mate, but symmetry plays a key role.  The manifestation of secondary sexual characteristics that affect appearance influences competition over mates more so than any other features.  Symmetry, or a lack thereof, impacts the way creatures approach the process of mate selection.  For example, in cases involving dominance standings among fallow deer, human attractiveness, and mating success in certain types of song birds (Cooley 2004), the importance of symmetry is evident Across various studies, facial and body symmetry seem to show up as signs that highlight an organism’s developmental stability and other positive characteristics that would make a person or creature a more desirable mate choice.

Let us first examine the reasoning behind the attractiveness of a symmetrical appearance that occurs especially in humans.  Primarily, a symmetrical facial area and body suggest solid genetic composition; the risk of mutations and susceptibility to various diseases is minimal.  This in turn increases attractiveness (Little 2008).  Going back to our biological roots, organisms seek mates that will allow them the best chances of successful reproduction.  This desire for symmetrical physical traits is said to be an evolutionary habit developed to pick up on those individuals with the best the highest quality genetics (Simmons 2004).  A lack of genetic flaws and a presence of healthy characteristics makes an individual more appealing as they seem to provide better odds of procreation.  In humans, bilateral symmetry is a very important factor when it comes to attempting to determine the quality of genes.  Fluctuating asymmetry (FA), or the asymmetrical characteristics found in traits that, across a population, are typically the same, demonstrate individuals of a lesser quality (Penton-Voak 2001).  The presence of FAs demonstrates an organism’s inability to cope with environmental or genetic challenges (Thornhill et al 2003).

The same face, edited, can come across more appealing as symmetry hides obvious signs of potential genetic problems

The same face, edited, can come across more appealing as symmetry hides obvious signs of potential genetic problems

According to a study by Anthony Little and Benedict Jones (2006), perception also plays a major role in the processing of symmetry during mate selection.  The body’s ability to more easily read and comprehend visual stimuli supports the tendency of people to appreciate symmetry in a partner.  This backs up the fact that although people are quick to judge an individual’s level of attractiveness, it is difficult to precisely define which physical traits make that person appealing, or even which traits in general can be considered attractive from one person to another.  An experiment by Marianne Peters, Gillian Rhodes, and Leigh Simmons sought to test not only attractiveness of facial symmetry or the appeal of bilateral symmetry of the body, but both together at the same time (2006).  In this study, the team discovered that in the case of women viewing males, facial symmetry had a positive correlation with attractiveness.  Both body and facial symmetry had a positive correlation when men judged the attractiveness of females.

Bar Chart

A series of experiments performed by Dahlia Zaidel and her team (2004) provides evidence that symmetry or asymmetry does not necessarily help or hinder chances of mate selection.  Between the categories of symmetry and health, there was no significant difference.  However, when it came to the categories of symmetry and attractiveness, the difference was indeed significant.  A significant difference also existed for the relationship between attractiveness and health.  These data essentially stayed the same, no matter the gender of the subject.  A mate, even if asymmetrical in certain aspects, may still be selected because sometimes novel traits add to the appeal of an individual and thus make them attractive.  Symmetry does not immediately or certainly indicate the health of a potential mate.  Rather, symmetry impacts the perception of attractiveness.  It seems that in some cases, the pure level of attractiveness plays the defining role in mate choice, and perhaps deciding the health and genetic strength of a mate under inspection for selection.

face vs body attractiveness

In any case, the importance of symmetry on various levels can be seen in humans and animals alike.  Both have the pattern in which females tend to demonstrate preferences and males try to garner attention.  Those males, especially, that find themselves lacking symmetry work harder to gain the attention of the females.  Hopefully they possess a brighter orange coloring that will draw the attention of females, but if not, they must seek other means.  In order to be able to compete for the consideration of different females, less symmetrical males must put forth their good sides for consideration.  Sometimes they try to “cheat” their ways into favor, as they are not as physically capable as other males, but still attempt to work their way to the top and get noticed.  For example, female guppies are attracted to bright orange pigmentation in potential mates, as well as symmetrical placement of spots along the bodies of the males.  While showing himself off to a particular female, a male guppy will frequently and quickly swim while alternating the side exhibited to said female.  This process makes it difficult for a female guppy to fully observe the location of the spots and prohibits a greater sense of spot symmetry or asymmetry (Gross 2007), and thus, those male guppies that may not be found as attractive have a better chance of being selected as a mate and successfully reproducing.

Guppy chart

a) Female preference = males who are more orange

Cicadas also go through a process of attempting to disguise asymmetrical qualities and hope that females focus on the positives.  After John Cooley’s study of these insects (2004), it was discovered that those male cicadas with various asymmetries were not hindered by them in the area of being selected as a mate.  Granted, there were some features, such as those cicadas with asymmetrical venation, that inhibited the majority of the members possessing that trait from being successfully chosen as a mate.  Overall, though, in the case of these cicadas, the females did not solely reject possible mates due to a lack of symmetry.  They actually seemed to make their mate choice based upon the cicada as an entire unit, rather than one asymmetrical or extraordinarily symmetrical aspect of it.  However, the scientists noticed that there was one factor that did seem to positively impact mating success.  There were some male cicadas that exhibited asymmetrical forelegs.  This did not seem to hamper them, but rather, the males with asymmetrical forelegs actually had more success in being selected by the females to be a chosen mate.  A hypothesis of this occurrence is that longer forelegs give some of the cicadas the ability to move faster and come in contact with a signaling potential female mate faster than another male.

Lizards, too, undergo an evaluation of their symmetrical or asymmetrical characteristics by the females of the species.  The Iberian rock lizards are inspected by the females based upon chemoreception.  Males use chemoreception to attempt to win the females over.  The females can tell much about a potential partner from the scent that is within the mixture the males excrete.  The chemical cues used by the female lizards help to indicate the symmetry of a potential mate (Martin 2006).  Red junglefowl, or Gallus gallus, also exhibit a tendency to manipulate symmetry and use their asymmetry to their advantages.  The males of this species have multiple ornaments, but the individuals who ran the experiment realized that the females did not seem to immediately have one direct line of attention for the ornaments that the junglefowl boast, but that they would later go on to use plumage as a determining factor (Ligon 1998).  Preference for symmetrical features was even found to be prevalent in females of swordtail fish (Merry & Morris 2001).  Scientists thought that females, if following the equation they had laid out, would seek the males with more bars.  This, however, was not the case at all.  The females were drawn to, and spent more time with, the males with symmetrical bars.

When it comes to selecting a mate, humans are not the only beings that seek symmetry in a partner.  Other creatures, whether they be insects, reptiles, fish, or birds, also seek symmetry when going through the process of mate selection as it has a tendency of indicating health and dependable genes.  Although organisms will often attempt to down play their asymmetries, they still can negatively impact the chances of a being to reproduce.  Occasionally, asymmetries aid a creature in its quest to impress and gain a mate, however more frequently than not, those individuals displaying characteristics that are not symmetrical will probably be overlooked in favor of a mate that demonstrates robust genes and an ability to survive changes within its genes or those changes brought about by the environment.  Humans especially seek symmetry in both faces and bodies (mainly due to the fact that it is easier to identify health issues signaled by a lack of symmetry).  If research on such subjects continues, perhaps we can come to fully understand the reasons behind what attracts individuals to choose the mates they do.  The role that mate selection plays on a day to day basis in society is a large one, both on conscious and unconscious levels.  Over all, symmetry is the key factor in deciding mate choice as it influences attractiveness and also acts as a type of signal for safe procreation.  Without this tip, mate selection would have to follow an entirely new and different course.

Works Cited

Cooley, John R.  “Asymmetry and Mating Success in a Periodical Cicada, Magicicada

septendecim (Hemiptera: Cicadidae).”  Ethology.  (2004):  745-759.

Gross, Mart R. et al.  “Courtship and Genetic Quality:  Asymmetric Males Show Their Best Side.”  Proceedings of the Royal Society.  (2007):  2115-2122.

Ligon, David J. et al.  “Mate Choice by Female Red Junglefowl:  The Issues of Multiple Ornaments and Fluctuating Asymmetry.”  Animal Behavior.  (1998): 41-50.

Little, Anthony C. and Benedict C. Jones.  “Attraction Independent of Detection Suggests Special Mechanisms for Symmetry Preferences in Human Face Perception.”  Proceedings of the Royal Society. (2006):  3093-3099.

Little, Anthony C. et al.  “Symmetry and Sexual Dimorphism in Human Faces:  Interrelated Preferences Suggest Both Signal Quality.”  Behavioral Ecology.  (2008):  902-908.

Martin, J., Lopez, P.  “Links Between Male Quality, Male Chemical Signals, and Female Mate Choice In Iberian Rock Lizards.”  Functional Ecology.  (2006):  1087-1096.

Merry, Justin W. and Molly R. Morris.  “Commentaries:  Preference for Symmetry in Swordtail Fish.”  Animal Behavior.  (2001):  477-479.

Penton-Voak, et al.  “Symmetry, Sexual Dimorphism In Facial Proportions and Male Facial Attractiveness.”  The Royal Society.  (2001):  1617-1622.

Peters, Marianne et al.  “Contributions of the Face and Body to Overall Attractiveness.”  Science Direct:  Animal Behavior.  (2007):  937-942.

Simmons, Leigh W. et al.  “Are Human Preferences for Facial Symmetry Focused on Signals of Developmental Instability?”  Behavioral Ecology.  (2004):  864-871.

Thornhill, Randy, et al.  “Major Histocompatibility Complex Genes, Symmetry, and Body Scent Attractiveness In Men and Women.”  Behavioral Ecology.  (2003):  Vol. 14, No. 5:  668-678.

Zaidel, Dahlai W.  “Appearance of symmetry, beauty, and health in human faces.”  Brain and Cognition.  (2005):  261-263.

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