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Archive for April, 2009


Attraction is one of the most complex processes humans and animals participate in, because the subtleties we are aware of only represent the surface of how we determine attraction. Sexual attraction refers to a person being drawn to another in order to have a sexual relationship. The meaning of a sexual relationship differs across cultures and history. Much of human sexual attractiveness is governed by physical attractiveness. Certain aspects of what is considered attractive are universally agreed upon across the human species.

Internal factors such as reproductive potential control our external behaviors and responses to sexual attraction.  Reproductive potential is defined as the individual’s ability to invest in the growth, development, and social reproductive competencies of offspring. Human mate selection refers to the characteristics and values considered in choosing a mating partner in order to increase the probability of reproductive success (Buss et al., 2001). Principles of reproductive fitness do not guarantee reproductive success. Meaning, mate selection occurs through evolved principles that increase reproductive success. But actual success depends on multiple factors including biological, social, environmental characteristics.


The evolution of sexual selection is an adaptive process whereby organisms change directionally over time. The basic premise of evolutionary theory, with regard to mate selection, is that human organisms will select mates that maximize their chance of reproductive success. Reproductive success will be influenced by multiple factors such as investment, reproductive characteristics, and environmental concerns. The success of an organism is not only measured by the number of offspring left behind, but by the reproductive fitness of the offspring.

The sexual selection theory proposed by Charles Darwin states that the frequency of traits can increase or decrease depending on the attractiveness of the individual. He also hypothesized that sexual selection could be what caused differentiation  among human races, as he did not believe that natural selection provided a satisfactory answer. Drawing on some of Darwin’s largely neglected ideas about human behavior, Geoffrey Miller a social biologist has hypothesized that human culture arose through a process of sexual selection. He argues that cultural traits such as art, music, dance, verbal creativity and humor are of no survival value. Miller is critical of theories that imply that human culture arose as accidents or byproducts of human evolution. He believes that human culture arose through sexual selection for creative traits. In that view, many human characteristics could be considered subject to sexual selection as part of the extended phenotype, for instance clothing that enhances sexually selected traits.

Mate selection inherently involves consideration of the reproductive characteristics of the potential mate. An ideal mate would possess desirable genes to increase the likelihood that offspring will develop into healthy, reproducing adults. Analyses of mate selection processes find mechanisms or strategies that organisms use to identify the potential health of a mate. Such mechanisms increase the attraction or desire of organisms to mate with one another.

Sexual attractiveness in non-human animals depends on a wide variety of factors. Often, there is some element of the animal’s body which exists for sexual attraction, like the bright plumage and crests of some species of birds. In many species, there are behaviors which appear to be sexual display. Some of these attributes seem to exist solely to demonstrate fitness and health, by demonstrating the ability to sustain a biologically expensive. Conversely, the receiving sex may be predisposed to perceive these features as sexual attraction. It is possible that these features by the giving or the receiving ends cause major survival problems, especially where a direct competitive element is involved.


While social customs, culture, and technology are constantly changing, our brains and bodies have been handicapped to the slow pace of evolutionary time. As in they haven’t had time to change in any significant way during the few thousand years since we were all hunters and gatherers, when our only job was survival. Survival means one thing: staying alive long enough to reproduce, so that the next generation can stay alive long enough to reproduce. The way the primal section of our brains are designed, nothing else matters besides survival.

 A few hundred million years ago, a creature came along and thrived, because instead of eating its young, it cared for them. Some of the earliest ones laid eggs, and had a pouch for carrying the infanst and nipples for feeding them. These evolved into creatures that, instead of laying eggs, gave birth to live young and took care of them until they had developed relative independence. But in order to have those kinds of interactions required a more complex brain. A new layer of brain material developed controlling emotional responses called the limbic system. As these new creatures, called mammals, evolved further, the limbic system grew in size and complexity. The limbic system allowed the ability to learn new responses, as well as hold a complex memory that allowed learning. But the most remarkable ability the limbic system gave these creatures was the ability to assess the internal state of another animal. Mammals and reptiles both make noises through which they can transmit information, but mammals are capable of a much richer variety of language, creating a drastically different means of communicating.

When your brain was fashioned by natural selection, the first man who impregnated a woman had a good chance of dominating her reproductive years. Some thousands of years ago, women were either pregnant or nursing almost continuously from puberty until death at a young age. Since nursing inhibits ovulation, this reduced the chances of becoming pregnant. The reason men of any age continue to find youthful qualities attractive in females is that they were designed to get them pregnant and dominate their fertile years by keeping them that way. In many cultures, it’s perfectly acceptable for a man to take a second wife, who is usually younger. In our culture, its considered taboo, yet the advertisements for it are everywhere. Only our opinions about this process has changed, not our innate machinery.


The human face can be seen as a complex, characteristically unique pattern that helps us distinguish people (Vezjak and Stephancic 1994). Faces, in general, are involved in reproductive behavior among humans. Couples faces resemble each other much more than random pair formation would suggest. Similarities between faces are not likely to arise as a result of pair formation or environmental factors (Rice and Borecki 2001), as facial features have a strong genetic basis. Facial resemblance between couples has been extensively reviewed (Penton-Voak and Perrett 2000) and can certainly be viewed as an adaptive trait produced from evolutionary forces. Human faces are even considered as a communication device for signaling heritable traits (Thornhill and Gangestad 1999) and aid in the search for mates with “good genes”.

Facial expression is a universal form of communication among mammals. This silent communication system is made possible by the fact that facial muscles are the only muscles in the body that attach directly to the skin, which allows for infinite subtleties of expression. Body language is nearly as expressive, with its infinite variety of attitudes to display emotion. At least on a basic level, most people recognize that what you say is often far less important than how you say it. And how you say it involves powerful and complex messages sent by facial expression, body language, tone of voice, and even scent. Making this all the more difficult is the fact that much of this communication takes place beyond the reach of our conscious awareness. The explanation for feelings of comfort and uncomfortable lies in the complex communications transmitted through facial expression, body language, and other unconscious physical signals, including smell. As you look up the evolutionary ladder, one finds an increasing tendency among mammals, especially in primates, to mimic one another. This is done unconsciously and automatically as a means of communication. We signal our emotional states externally through facial expression and other forms of body language, such as posture. Seeing these unconscious signals in another individual initiates an involuntary need to mimic such behavior.

When two individuals send information through this subconscious communication system, they not only catch each other’s emotional state, but their heart rates, breathing, speech patterns, and skin conductance all synchronize as well. Studies using high-speed cameras demonstrate how this system works. Complete shifts in facial expression, from a happy smile to a horrified grimace and back to a smile, can take place within a fifth of a second, too quickly to register in our conscious minds. Two people who are communicating in this way will synchronize their speech patterns and rhythms within as little as a 20th of a second.  When it comes to men and women interacting like this, the effects can be profound, and virtually irresistible. In one experiment, psychologists paired men and women and told them to gaze into each other’s eyes for 2 minutes. As potential lovers become comfortable, they pivot or swivel until their shoulders become aligned, their bodies face-to-face. When he crosses his legs, she crosses hers; as he leans left, she leans left; when he smoothes his hair, she smoothes hers. They move in perfect rhythm as they gaze deeply into each other’s eyes. Afterward, they experienced greater feelings of romantic love, attraction, interest, warmth, and respect than control groups felt.  These results are more interesting considering conversation was not involved in the experiment. Called interactional synchrony, this human mirroring begins in infancy. By the second day of life, a newborn has begun to synchronize its body movements with the rhythmic patterns of the human voice. And it is now well established that people in many other cultures get into rhythm when they feel comfortable together.


An interesting area of relatively new research has found connections in gene selection and bio-chemical signals of fertility. Frequently, especially in insects, chemical signals are used to generate sexual interest and to locate potential mates. These signals, known as pheromones, are hormones produced in the skin are used to influence behavior in others. In humans, research has led us to believe that these signals are received and translated in the vomeronasal system, located alongside the nasal septum. Interestingly, the most powerful scents are the ones that most of us can’t consciously detect. Both men and women give off pheromones called androstenes, but men emit more of them. Women secrete lipids known as copulins in their vaginas. Both are used as powerful communication channels that humans are obliviously to. When women are exposed to androstenes, they feel better and find that people look better to them. When androstenes were applied to chairs in a theater and a dentist’s office, women chose those seats, while men rejected them. Astrid Jutte, a researcher who worked at the Ludwig Boltzmann Institute for Urban Ethnology, in Vienna, exposed men to synthetic copulins and found that it increased the men’s testosterone levels by 50 percent. The test subjects also rated women’s faces and voices as more attractive after the men had smelled copulins, even though they either could not detect the smell or didn’t find it pleasant. Since a woman’s sense of smell is also most acute during ovulation, men and women are biologically tuned to read each other by smell alone in such a way as to increase the chances that they’ll reproduce. (Geary et al., 2004).

There are powerful and complex messages encoded into those smells; which are produced by our immune systems. Essentially we are sampling each other’s genes when we take in copulins and androstenes, particularly the genes of the so-called major histocompatibility complex (MHC). MHC genes are the ones that detect foreign organisms, like bacteria. This allows us to tell by smell alone how closely someone is related to us. Researchers have shown that people choose mates whose MHC is least like their own. A Swiss researcher gave women T-shirts that had been slept in by men and asked them if they liked the smell. The women preferred the ones from men who were genetically different, and thought the others smelled like their brothers or fathers.

Researchers found that fetal loss increased significantly when parents shared all the genes of the HLA system, or just genes in the HLA-B region. When the time came for these males to choose mates, they avoided females whose MHC genes were similar to their foster mothers’, even when that meant winding up in the position of mating with a female whose MHC genes were similar to their own. These results suggested that animals might somehow be able to detect prospective mates whose MHC genes are more or less similar to their own, and then to choose mates accordingly. They may have evolved such an ability because of MHC’s importance in the immune system, or simply because MHC sensibility is a way to distinguish relatives from nonrelatives, thus avoiding inbreeding. If odor does provide information about the immune system, it makes evolutionary sense for women to pay special attention to smell. They have much to lose if they mate with an inappropriate male and give birth to a baby with a reduced ability to fight off disease.


Despite a wide range for standards in beauty and sex appeal, there are however a few widely shared preferences. It is to a males’ genetic advantage to fall in love with a women who will produce viable offspring; as it is to a woman’s biological advantage to become captivated by a man who can help support her young. The appearance of health also plays a part in physical attraction. Men and women around the world are attracted to those with good complexions. Everywhere people are drawn to partners whom they regard as clean. Often, women with long hair are thought to appear more beautiful, as the ability to grow long, healthy looking hair is an indication of continuous health of an individual. Hair is a visible record of not only a woman’s health, but her history, too. It takes about 3 years to grow shoulder-length hair, and since it’s not essential to survival, it suffers if the individual becomes very sick. Hair reveals our diet, our habits, and our aesthetic choices. Another indication of health of an individual is the ability to grow long, strong, healthy-looking fingernails. The preference for this effect has resulted in the fact that artificial nails and manicures have grown extensively popular for women beginning in the 20th century. Healthy-looking skin is also considered a beauty trait.  Other signals of human female reproductive capacity are big breasts accompanied with a small waistline that accentuates her hips; this demonstrates to the prospective male that she can carry a child. Researchers have found that women with the classic hourglass shape are twice as likely to become pregnant as women with other shapes. And to top it all off, women use clothing to accentuate these aesthetically pleasing features.


The human mating process is so systematic that women from around the world flirt with the same sequence of expressions. First the woman smiles at her admirer and lifts her eyebrows in a swift, jerky motion as she opens her eyes wide to gaze at him. Then she drops her eyelids, tilts her head down and to the side, and looks away. Frequently she also covers her face with her hands, giggling nervously as she retreats behind her palms. Eye contact seems to have an immediate effect. The gaze triggers a primitive part of the human brain, calling forth one of two basic emotions—approach or retreat. You cannot ignore the eyes of another fixed on you; you must respond. This sequential flirting pattern is so specific that many researchers are convinced it is innate; a human female courtship strategy that evolved eons ago to signal sexual interest.

With flirting comes the personality factor of attraction. Research has confirmed that a good sense of humor is an important human mate preference worldwide. When people are asked to rate the importance of various traits for romantic relationships, a good sense of humor is consistently at or near the top of their, sometimes outranking physical attractiveness. There is also evidence that the preference for humor may be stronger in seeking romantic partners than in seeking platonic friends (Sprecher & Regan, 2002). Also, the preference for humor seems to increase with the duration of the relationship: we seem to value humor especially in long-term mates.


Although sexual strategies and attraction triggers greatly differ at the individual level, the timeless practice of human courtship seems embedded into the human psyche through the process time, selection, and evolution. There is such mystery associated with attraction; we are literally not wired to understand, just to act. By the time the first words are spoken, a man and woman already know each other’s intentions. Attraction is a complex process our success as a species depends on and is too important for our conscious minds to understand.



1.      Buss, David M. and Schmitt, David P. Universal Dimensions of Human Mate Preferences. .Bradley University, University of Texas; 2005.

2.      Mabbott, Donald J. and Bisanz, Jeffrey. “Computational skills, working memory, and conceptual knowledge in older children with mathematics learning disabilities” Journal of Learning Disabilities (2008)

3.       Geary, David c. and Vigil, Jacob and Byrd-Cravrn, Craven. “Evolution of Human Mate Choice.” Journal of Sex Research (2004)

4.      Thornhill, R., & Gangestad, S. W. (1999). Facial attractiveness. Trends in Cognitive Sciences, 3, 452-460

5.      Gangestad, S. W., Simpson, J.A., DiGeronimo, K., and Biek, M. (1992). Differential Accuracy in Person Perception Across Traits: Examination of a Functional Hypothesis. Journal of Personality and Social Psychology 62(4):688-698.


6.      Gangestad, S. W., & Simpson, J. A. (2000). On the evolutionary psychology of human mating: Trade-offs and strategic pluralism. Behavioral and Brain Sciences, 23, 573-587


7.      Gangestad, S. W., & Thornhill, R. (2003). Facial masculinity and bodily fluctuating asymmetry. Evolution and Human Behavior.


8.      Thornhill, R., & Gangestad, S. W. (in press). The evolutionary psychology of human physical attractiveness. In A. Moya & E. Font (Eds.), Evolution: From molecules to ecosystems. Oxford, UK: Oxford University Press.


9.      Urbaniak, Geoffrey C.  and Kilmann, Peter R.  “Physical attractiveness and the nice guy paradox: do nice guys really finish last?” Sex Roles: A Journal of Research. Nov, (2003)










17.  Anatomy of Love; The Natural History of Monogamy, Adultery, and Divorce, by Helen E. Fisher. Copyright C 1992 by Helen E. Fisher. Reprinted by arrangement with W. W. Norton & Co., Inc. Psychology Today © Copyright 1991-2009 Sussex Publishers, LLC, New York, NY

18.   Love with the Proper Stranger,by Meredith F.Smal.  Natural History.Copyright the American Museum of Natural History, 1998.


19.  Buss, D. M., & Schmitt, D. P. (1993). Sexual Strategies Theory: A contextual evolutionary analysis of human mating. Psychological Review, 100, 204-232.


*  20. Greiling, H., Buss, D.M. (2000). Women’s Sexual Strategies: The hidden dimension of extra pair mating. Personality and Individual Differences, 28, 929-963