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Sexual Attraction, Evolution, and Biology
August 4th, 2008 02:45 Afternoon EDT
By Cindy Adams
Link to the article
Successful copulation and reproduction has been propagated by the human species for millions of years. This process has been studied and researched for centuries to determine the physiological and psychological motivations behind procreation and sexual attraction. Darwin and his theory of evolution, the survival of the species, and natural selection, viewed the process of mating and reproduction as purely driven by biological forces. For human beings to survive and ensure their genes lived on, certain partners had to be chosen, all based on biology and gene fitness. Even the human orgasm is biologically driven regarding mating and the various sexual practices between men and women. This also controls much of what men and women find attractive in a mate and may sometimes override psychological and social desires. Therefore, although the modern human brain has the ability to make rational decisions when choosing a mate, sexual attraction is still the driving force behind partner choice.
Darwin's Theory of Evolution
Charles Darwin's theory of evolution has been a topic of controversy since it was promulgated in the late 1800s. Nonetheless, its tenets remain strong, with many modern day scientists making discoveries that support Darwin's theories of evolution, natural selection, and survival of the fittest. In The Origin of Species, Darwin calls the process of natural selection or survival of the fittest, the preservation of favorable individual differences and variations, and the destruction of those, which are injurious. Darwin's theory of evolutionary change and process of natural selection surmises that variations exist in every population of species. Organisms compete for the limited resources available to them, and may produce more offspring that can naturally survive, therefore, only a few organisms are successful in leaving progeny. Each organism passes on genetic traits and characteristics to their offspring, and the organisms that inherit the most beneficial traits are more likely to survive and reproduce. Homologous traits are those found in different species that are structurally and functionally similar in nature and that arose through genetic ancestry. Those animals that have the greatest number of homologous traits are more closely related than those with fewer homologues. Alternatively, analogous traits are structurally and functionally similar to one another, but did not come about through genetics, and have arisen independently on more than one occasion.
Behavioral traits evolve during various adaptations through mating, hunting, means of cooperation, and methods of escaping predators. This evolution takes place through changes in neural or brain mechanisms, hormonal changes, and patterns of learning, thereby revealing physiological and behavioral systems evolving in concert with one another. An example of this behavioral evolutionary process is the "fight or flight" response that humans have been genetically disposed to in order for early man to be able to escape dangerous predators. This stress response filled the human body with strength, stamina, and speed to escape a hazardous situation, and those who fought and won, or fled and lived, were the fittest and survived. In Western civilization today, this response is no longer needed for survival, however, the body still responds to stressors with this "fight or flight" response. Therefore, the behavior this response is meant to coincide with has evolved into one in which modern day stress is the "predator", rather than a wild animal or a competing tribe.
Successful Reproduction and Survival of the Fittest
Finding the right partner in primitive society made the difference between the life and death of an offspring. Darwin theorized that sexual admiration could interfere tremendously with the struggle for survival. However, he also postulated that females choose their male partners carefully; evaluating which males will provide the best genes to contribute to successful reproduction and healthy offspring.
Because reproduction is the key to survival of the human species, men appear to have developed a short-term sexual strategy, as men who pursue multiple partners are more likely to out-reproduce men with one partner. Therefore, men's mating strategies includes a desire for sexual variety making the chances higher that if reproduction is not successful with one female, it will be with another. According to the journal article Sex Differences in Sexual Psychology Produce Sex-Similar Preferences for a Short-Term Mate:
Men desire nearly five times as many sexual partners than do women over a lifetime. Men's sexual fantasies also reveal a psychology attuned to sexual variety. Men's sexual fantasies more than women's sexual fantasies include multiple and unfamiliar partners.
This modern day psychology of the human male is no doubt an offshoot from his male ancestors who were physiologically prompted to over-reproduce to insure survival of the species.
Women, on the other hand, do not appear to have such a physiological need to procreate with multiple males, as women do not compete with other females in terms of reproduction during sexual encounters. Therefore, short-term sexual partners for women may function only to evaluate possible long-term mates, and serve more of a social function whether than a sexual or reproductive one.
Choosing a Mate By Force
In their controversial book, A Natural History of Rape: Biological Bases of Sexual Coercion, Thornhill and Palmer assert that rape has a biological bases in evolution. Their assertion is that all men are potentially rapists and forced mating enables men who are sexually disenfranchised to procreate. Thornhill and Palmer even go so far as to suggest that young men should be told of the evolutionary basis of their "natural urge to rape," and should receive special training regarding self-control to manage their biological urges:
Completion of such a course might be required say, before a young man is granted a driver's license. Such a program might start by getting the young man to acknowledge the power of their sexual urges and then explaining why human males have evolved to be that way.
In addition, Thornhill and Palmer's advice to young women is just as ludicrous, when they state, "Young women should be made aware of the costs associated with attractiveness...and it should be made clear that, although sexy clothing and promises of sexual access may be means of attracting desired males, they may also attract undesired ones." This assertion is a "blame the victim" stance that virtually forgives a male rapist's behavior due to the female acting in a "perceived" provocative manner and the male not being able to control his actions. In addition, Thornhill and Palmer posit that in evolutionary history, women who were been raped had increased fitness as a result of mental pain because this pain forced them to consider the social circumstances that caused them to be raped. Hence, this mental pain is similar to physical pain as it caused the victim to reevaluate their behavior and circumstances to avoid a repeat of this pain inducing action in the future. In addition, Thornhill and Palmer state:
Human rape victims rarely show much sexual arousal and almost never achieve orgasm. It is conceivable that some aspects of woman's capacity for orgasm evolved in the context of reducing the fertilizing capacity of rapists' ejaculates. That is, the absence of orgasm during rape may be an evolved response to rape.
Fortunately, critics have found the authors' assertions shocking and preposterous and have dismissed Thornhill and Palmer's hypothesis regarding the male desire to rape as an evolutionary necessity, along with the female victim's role in the violent act as a learning experience to evoke mental pain for survival.
Evolutionary Function of Orgasms
Both male and female humans have orgasms, however, many theorists have pondered as to what physiological role the female orgasm has, if any, in the sexual act and reproduction. Further, until about 25 years ago, when female scientists became active in anthropology and evolutionary psychology, female sexuality in the scope of human evolution was a neglected topic.
The male orgasm results in ejaculation of sperm for reproduction purposes; however, there has been no clear explanation for the biological or evolutionary function of the female orgasm. Female orgasm is not necessary for reproduction and does not happen every time the female copulates, therefore, several hypotheses have been offered to explain this irregularity. Sperm competition is one hypothesis, and predicts that when sperm of different males compete to fertilize the eggs of one female, sperm competition occurs. Baker and Bellis conducted a study in which they found that 30% of women sampled in a British study claimed to have been inseminated within a 24-hour period by two different men. There is also evidence that ovulating women seek out extra pair copulation more than those women who are non-ovulating. Therefore, the female orgasm may be an adaptation to promote conception from males of high genetic quality. Yet, another study has indicated that female orgasms may actually promote fertilization during copulation. Levels of oxytocin, a naturally occurring hormone in humans, increase following an orgasm. In the journal article, The Case of the Female Orgasm: Bias in the Science of Evolutions, Puts demonstrated that:
treatment with this hormone caused uterine contractions lowered uterine pressure and rapid movement of a semen-like substance into the uterus...female orgasms within 1 min[ute] before and 45 min[ute] after ejaculation were associated with higher sperm retention than was no orgasm or orgasms at other times.
Therefore, this study lends credence to the idea that the female orgasm is a physiological response designed to increase the likelihood of conception. However, the psychological component of the female orgasm is still not fully understood and may be related to the attraction and desire she has for her male partner, just as the male human's appears to be for her.
What Men and Women Find Attractive
In order for males and females to engage in healthy sexual behavior, an attraction must exist between the two. However, levels of attractiveness, and what both men and women consider attractive appear to be a function of both evolution and psychology.
A round buttock is another sexual "turn-on" as "Humans have evolved from animals that walked on all fours, when the bottom was a big turn-on to males, who would mate from behind" as reported by Morris in his book, The Naked Woman: A Study of the Female Body. Further, such curves in women have also evolved as attractive because women needed a layer of fat to keep themselves and their babies alive during times of famine, and this fat was spread across the body evenly creating rounded curves. Additionally, a woman's higher voice, doe-like eyes, and lack of body hair are traits they share with children. Men have evolved to protect their children from harm; therefore, these "childlike" features make women more attractive to men. Psychological adaptations have evolved as well, leading to physical attraction. For instance, men who spend more time away from their partners show a greater interest in copulating with their partners and find their partners to be more physically attractive.
Women have certain traits in men that they find physically appealing. Women find larger than average eyes attractive, a large smile and prominent cheekbones, which appears to be related to androgen levels indicating lack of illness. It is interesting to note that studies have indicated that less-attractive females seek less-masculine males who have slightly feminized faces for relationships. This may be more of a psychological function than that of physiology, indicating that if a female or male perceive themselves as less attractive, they may be drawn to someone of the opposite sex who tends to mirror a lower self-image.
The Scent of a Mate
It was once thought that humans, along with apes, had a very poor sense of smell compared to other creatures in the animal kingdom, citing that the "hardware" was missing for "communicating by scent Pheromone reception" that other animals possessed. I his article entitled, The Smell of Love, Bryant reported that this entailed having two little "pits" in each nostril known as the vomeronasal organ (VNO). However, smell researchers have determined that a simple kiss has evolved in the Western world from the universal human greeting of smelling one another's hands or faces. These areas of he body "are the two most accessible concentrations of scent glands on the human body besides the ears." Although such smells are not blatant, and may not register in the conscious mind, such smells influence mood and sexual mating preferences.
Tests were conducted at the University of Bern in Switzerland using 100 college students, with the male participants having worn untreated cotton T-shirts during their slumber for two consecutive nights. These males were instructed not to eat spicy foods, use deodorants, cologne, perfumed soaps, and not to smoke, drink, or have sex during those two days. The T-shirts were kept in sealed plastic containers when not being worn. Subsequently, the female participants, who had used nasal spray two weeks prior to the test, were instructed to sniff new unworn shirts as a control for the study; after which they were "asked to rate each man's shirt for sexiness,' pleasantness,' and intensity of smell.'" It was determined that how women rate the sexiness and pleasantness of a man's body odor depends upon how much of their major histocompatibility complex (MHC) codes are shared. The more similar a man's MHC profile, the less the female participant preferred the smell, because MHC-similar men's smells were more often described as being like a father's or brother's body odor. MHC is a segment of DNA that is disease detecting. When a disease is recognized through MHC, T cells are alerted and smother the disease with destructive enzymes. The results would indicate that there is an evolutionary process through scent that ensures incest or inbreeding is avoided, since such relationships can create mutations and other problems within the gene pool. In line with this reasoning, Bryant reports, "Couples experiencing difficulty conceiving a child-even after several attempts at tubal embryo transfer-share significantly more of their MHC than do couples who conceive more easily."
In addition, Swiss researchers found that women taking birth control pills reported reverse preferences regarding MHC and smell. This means that a woman may feel attracted to a man she may not normally find attractive or notice if she were not on birth control, however, since her body chemistry is altered with oral contraceptives and she is not able to reproduce, her choices for mates is less risky and the spectrum of men she may be sexually intimate with sans the risk of pregnancy is increased. The research and knowledge regarding human smell, sexual attraction, and mating indicates that our olfactory senses may be much more important than originally thought in choosing a partner to with whom to reproduce.
Homosexuality and Biology
There is significant controversy today regarding homosexuality being a conscious social choice or a biological determinant. Many assert that animals in nature do not engage in homosexual practices because it is "abnormal" and does not result in reproduction to propagate the species. However, BBC News has reported in an article entitled Oslo gay animal show draws crowds that according to experts, "homosexuality has been observed among 1,500 species, and...Homosexuality is a common and widespread phenomenon in the animal world...Not only short-lived sexual relationships, but even long-lasting partnerships; partnerships that may last a lifetime." This is evidence that the practice of homosexuality occurs in nature, and must therefore, have some genetic purpose and possible benefit to the species as a whole.
In his book, Straight Science? Homosexuality, Evolution and Adaptation, McKnight writes, "Homosexuality is a major puzzle for evolutionary theory, for if evolution has a purpose it is reproductive fitness, the passing of genes to our children." Natural selection should weed out the less fit of the species and those who carry genes for a certain genetic anomaly breed less and diminish their genetic representation in the population. McKnight indicates this should gradually flush out the "gay" gene since over several generations, homosexual men would produce less offspring and their genes would eventually fade from the gene pool. Biologically, this would mean that homosexuality has some function in nature, since well-adapted genes adapt and survive, and clearly, the genetic predisposition for homosexuality has done so, which was asserted by Hahn in his article, A Unique Theory on Population Control: With the Population Growing, Homosexuals May Save the World.
A study conducted in 2004, took a closer look at homosexuality and its biological precepts. According to the study reported in the journal Nature, "Homosexuality may be partly influenced by genetics. As Hahn indictes, the same genes that are proposed to predispose to homosexuality [in men] may also boost reproduction in women." In essence, if a family consists of both sons and daughters, and the daughters are capable of producing the required number of offspring to allow the species to survive, the sons are no longer needed to reproduce, which leaves them able to pursue other interests, rather than mating with the opposite sex to produce children. Hahn indicates, heterosexual men are programmed to produce more children than necessary to ensure offspring, therefore, homosexuality would have adapted as a means of population control.
Many studies have been conducted regarding psychology, sociology, and homosexuality, yet, unfortunately, clinical studies regarding biology and homosexuality have been scant and less than thorough. According to researchers "reporting on 144 studies of sexual orientation published in the Journal of Homosexuality from 1974 to 1993, found that only 10 percent of these studies used a multidimensional scale to assess homosexuality." Fausto-Sterling reported in the book, Sexing the Body: Gender Politics and the Construction of Sexuality, that only 13 percent of these studies used a single scale, many used self-identification, sexual preference, and behavior, and some academic publications failed to report the methods used in their studies.
In the article, Studies Put Genetic Twist on Theories about Sex and Love, Sileo writes that some have argued that just as heterosexuality is one biological expression of sexuality, so too may be homosexuality. Therefore, homosexuality may not be an isolated evolutionary aberration, but instead, part of a continuum of sexual behavior that is another variant in human sexual behavior.
Social vs. Sexual Attraction
Culture and evolution undoubtedly interact in every human endeavor, sometimes reflecting biological dispositions, and at other times working in the opposite direction. It has also been theorized that natural selection has a social component as well, since women are designed to invest heavily in their offspring, while men are programmed to achieve social status, primarily to attract women.
Darwin's theories suggest that natural selection, not culture, has shaped how we choose and court a mate. Therefore, over hundreds of thousands of years, evolution has been the driving force, which has molded everything from anatomy to the human psyche. This is to ensure that certain behaviors are favored and certain states of mind promote reproductive success resulting in survival of the species. Therefore, many question whether romance is guided by evolutionary biological and genetic mechanisms. Darwin's theories appear to remove emotion, love, and caring from the aspect of human relationships and inserts cold, hard scientific necessity in its place. Unfortunately, Darwin did not take into consideration the modern human brain, social pressures mating and relationships when he presented his theories.
This supports notions that culture may intercept genetics regarding our courting habits, as today couples have to deal with outside social pressures that may defy the laws of nature, or Darwin's survival of the fittest assertion. This is not to say Darwin's theory is not applicable to primitive man, it only means that Darwin's theories may be less relevant to the human species today than to other animals in nature who clearly remain reliant on biology and genetics for courting, mating, and reproduction behavior.
Furthermore, women may use short-term sexual partners to evaluate which males will be potential long-term partners. Characteristics of potential short-term partners that women found undesirable were already in another relationship, promiscuous, unfaithful, and sleeps around a lot, which supports the idea that women use short-term sexual relationships along with social factors for scrutiny. This would explain why women are much more selective about marriage partners than men are. According to Shapiro in the article, Not Silly Putty, "the science of human nature can inform us about the trade-offs involved in making decisions about the kind of society in which we want to live, and the extent to which our ideals are suited-or unsuited--to our instincts."
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