Biology Behind: Sexual Attraction among Humans

Greetings everybody, 
today we will be discussing sexual arousal/attraction and the biology that defines sexual preference. Sexual attraction is courting on the basis of sexual desire. “Attraction has a lot more to do with science and evolution than people might think” says Dr. Laura Berman. Unconsciously humans have evolved several mechanisms to enable us to pick out our perfect mates.
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Phenotypes and sexual  attraction

Facial symmetry is considered a sign of beauty and is an indication for good genes for reproductive health. In a study conducted by Joanna E. Scheib, Steven W. Gangestad and Randy Thornhill it was found that symmetry in males has an effect on sexual behavior as men with a higher degree of symmetry had more sexual partners compared to men with a lower degree of symmetry. According to a University of Edinburgh study symmetrical faces correlate with long term mental performance. Good facial symmetry is an implication that a male has experienced fewer genetic disturbances (e.g. genetic mutations) and environmental pressures (e.g. toxins and malnutrition) while growing. "If you choose a perfectly symmetrical partner and reproduce with them, your offspring will have a better chance of being symmetric and able to deal with perturbations." said evolutionary biologist Randy Thornhill of the University of New Mexico.

Aside from symmetry, structure of an individual’s face also gives an indication to fertility. Estrogen is responsible for the formation of a female's lower face, chin and brow, making them relatively small and short in order for eyes to appear prominent. On the other hand male faces are carved by testosterone, which helps establish a larger and square lower face, jaw and a prominent brow. Studies found that males preferred the more infant-like (small jaw, large eyes and defined cheekbones) female faces which indicated high levels of estrogen. Whereas female choice was depended on how far along the woman was in her menstrual cycle. Females prefer a male with a masculine face when ovulating and the more feminine one when not.

Image Source - Figures with WTH ranging from 0.9 to 0.5
Of Course, body’s proportions and shape play a vital part too. Waist-hip ratio signify reproductive health in both men and women. Sex hormones (testosterone in men and estrogen in women) determine where fat is stored on the body. If a woman creates the right combination and quantity of estrogen, her WHR(waist-hip ratio) will instinctively result with a body with a WHR in the desired range. Likewise individuals in the model hip-ratio range are less prone to diseases including cardiovascular disorders, cancer, and diabetes.

A WHR of 0.7 in western cultures is most desired in women. However males from South America and Africa preferred a WHR of 0.8/0.9. And a ratio of 0.9 in men’s bodies has been considered most attractive to women. However WCR (waist-chest ratio) plays a significant role in male attraction as broad shoulders and muscular chest with a slim waist (known as “V” shape) is often found attractive by females.

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Biochemical Odors

In the modern age today men and women spend vast amount of time on seeking a trademark scent that is found attractive by the opposite sex/same sex. But why? It only covers the natural odors scientists say that potential mates find most appealing. Odor affects us unconsciously and evolutionary biologists believe the sense of smell was heavily depended upon in an ancestral environment. A group of individuals (which might have included extended family) living together wouldn’t be able to determine whether they were blood-relative, to avoid incest with kin, it was likely that scent was used to avoid this. In a study by Anja Rikowski and Karl Grammer women rated the scent of t-shirts to classify whether the odor was attractive or unattractive. Females were more attracted to males with dissimilar MHC (major histocompatibility complex - a collection of genes that are related to immune systems) from their own in order to provide offspring a stronger and diverse immune system.

Odors let individuals know when a woman is fertile and when a man’s testosterone levels are high. When women are ovulating they secrete copulins a scent found appealing by men. Testosterone levels rise and men secrete androstenone an odor that repels women who aren’t ovulating. Usually a male can rate a female is attractive or not by looking at her photograph, however it was found that men who inhaled a low dose of copulins lost the ability to distinguish between an attractive and a less attractive female due to a rise in the levels of testosterone which reduces clear thinking.

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Cognition and attraction

Just like a drug, love and sexual attraction largely revokes around dopamine reward system in brain circuitry. Dopamine stimulates desire and reward by triggering an intense rush of pleasure.

The topics we have covered today can differ from person to person, however are all naturally a part of the human species.

Over and out.

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