Evolutionary Psychology of Sexual Mate(s) Selection in Humans
Updated: May 27
Key Words: Evolution, Reproduction, Sexual Selection, Territorial Polygyny, Parental Care, Sexual and Behavioral Dimorphism, Mating Strategies, Hypergamic, Dirty Old Men, Neoteny, Jealousy.
Summary: Evolutionary psychology is the combination of two science strong paradigms: evolutionary biology and cognitive psychology (computational theory of the mind). The behaviors that drive to the mate(s) choice that are exposed here correspond to their default biological configurations and hence are not morally justifiable because this would be to fall to the “Naturalistic Fallacy” which consist to argue that something is good because is natural (Pinker, 2002, 2008, 2009). Besides, these default behaviors are very modifiable by culture.
Everything in biology has to do with evolution and the latter is related to reproduction. This ensures that genes are passed to the next generation. And organism is just the way that genes have to make more copies of themselves (Dawkins, 1993). The majority of species reproduce sexually and sexual selection is the second type of selection proposed by Darwin (Dunbar et al., 2011).
Sex is something expensive regarding resources and time. Why don´t we reproduce parthenogenetically like clones? It has been traditionally believed that sex evolved to increase the variability of the descendants and hence improve the likelihood that some of the offspring survive should a sudden environmental change occur. But Pinker (2008, 2009) says that this should not be the case, because once an organism is adapted to its environment, it will not survive a rapid and drastic environmental change. Up to date, the best theory we have about the evolution of sexual reproduction is that it emerged as a defense against pathogens and parasites (Hamilton et al., 1990; Tooby, 1982). The idea is that an arms race has been stablished between us big organisms in one side, and pathogenic micro-organisms like bacteria and viruses in the other hand. In this war, we the hosts have developed immune systems and pathogenic micro-organisms have developed better ways to infiltrate us and look as if they were part the host to avoid being attacked by our immune systems. But virus and micro-organisms have very short lives, high mutational rates and have enormous population sizes and hence can evolve much faster than us, the hosts (Freeman & Herron, 2002). Sexual reproduction is a way to change the “immune locks or keys” in each hosts’ generation.
The human mating system is different to that of other animals, but it doesn’t mean that it escapes the laws that govern these systems. We are mammals, so the investment on behalf of females is greater than that of males. Women contribute with nine months of pregnancy, two or three years of maternal care, among many other things. Males contribute with some sex minutes and a spoon of sperm. We men are on average, 1.15 times bigger than women, which indicates that during our evolution men have been competing for women, with the consequence that some males mate more and others don’t get to do it at all, which results in polygyny (poly = several and gyn = female). And indicative, at least on apes (gibbons, orangutans, gorillas, chimpanzees and humans), on to what extend are females faithful or promiscuous in a species is the males testicles sizes (Weckerly, 1998). Chimpanzees females tend to be promiscuous and there is more possibility that a spermatozoon that fertilizes an egg, belongs to the male that has introduced more semen to the female. Hence, chimpanzee males have unusually large testicles in relation to their body size. In contrast, a gorilla is four times bigger than a chimpanzee, but their testicles are four times smaller. And that is because the females of a gorilla’s harem don’t have the opportunity to copulate with other males because the latter are twice bigger and therefore have monopolized his females. Men have smaller testicles, relative to our body size that chimpanzees, but our gonads are bigger than those of gorillas, which indicate that women are not wildly promiscuous but neither are monogamous all the time.
Human infants are dependent on their parents for a much larger period that what is seen in other species. And that is because we are born prematurely in addition to the fact that for our species learning is very important and therefore takes much more time compared with other species. So children, besides maternal care, need the resources of their male parents, which, among other things, proportionate meat for their development. This is very important because without animal protein, the human brain doesn’t develop adequately.
Like it happened in humans, paternal care may evolve when the offspring are vulnerable and easily defended by their fathers and when the latter can provide, in a relatively easy way, food concentrated on meat. When evolution produced devoted fathers, the mating game changed. A human female can choose a male based on his ability and willingness to invest on the progeny. In this case, men are not the only ones competing for females. Women also compete for males. Would that be the reason because human females are more visually noteworthy? But this competence is different between the two sexes: men will compete for fertile women who are willing to copulate, and human females will compete for men that are willing to invest resources on the offspring. A clarification must be done. Like in the majority of mammal species, in our ancestral hunters and gatherer societies, the territories and their resources where defended by males. So when a male has more resources to invest (in other words, has a better territory), females can do better sharing a winner male, which results in polygynyc arrangements, because a fraction of good quality resources of a winner male, may be better than all the resources of a looser male.
The competitiveness between males and the females’ selectiveness, are present in virtually all animal species. Sexual selection predicts that the members of the sex that invests less biological energy on reproduction (the males) will compete for the members of the sex that invests more in reproduction (females). A human egg is 85,000 times bigger than a spermatozoon (Wilson, 2004). The consequences of this gametic (gametes are eggs and spermatozoa) ramify in all the human sex biology and psychology. A woman is born with about 400 eggs, from a which around 20 can be converted to babies. In contrast, a man liberates around 100 million spermatozoa with each ejaculation. Once and egg fertilization is achieved, the merely physical work of a man has ended and both sexes benefit equally because the gene representation on the baby on behalf of each member of the couple is the same (50%).
The reproductive success of males varies and depends on the quantity of females they can gain access to. In other words, the reproductive success of males is given in quantity. The reproductive success of females doesn’t depend on how much males do they copulate with, because in the case of women, for example, they can only reproduce once in a year (pregnancy and breastfeeding). This is why the reproductive success of females is shown in quality. Bearing this in mind and in the case of humans, the breeding of and infant is long and complicated, so women have much more to lose if they choose wrongly their couple. Hence women are a lot more careful when it comes to choose a man. Is because of all these data that 90% of mammals species are polygamous, more exactly polygynyc. In humans is a little more complicated, because although is obvious that men don’t tend to be monogamous, they have the tendency to be more cooperative in the infants breeding, compared to other mammals. This limits a little, the possibility of men to seek other couples, so it is not a surprise that we, men, make a lot of emphasis on the fertility and reproductive potential of the female(s) that we choose (Dunbar et al., 2011; Evans & Zarate, 2010).
Related to this, another difference regarding sexual behavior between women and men, is that the latter, at the slightest sign of sex, get excited (Ellis & Symons, 1990; Moir & Jessel, 1992; Salmon & Symons, 2004). And this behavior has been seen in many other species. It wouldn’t have sense for women to get easily excited just by seeing a naked man, because a fertile woman will never fall short regarding sexual suitors, and in this market she can seek for the best available mate or obtain resources in exchange for her sexual favors. Men perceive feminine nudity as an invitation, while women can see masculine nudity as a menace. Contrary to men, women don’t seek to see images of unknown naked men with whom they could have sex, so there is virtually no pornographic market for women. The equivalent to the pornographic industry for women, are romantic novels, where sex is described within an emotional context and not in the succession of bodies pushing each other (Pinker, 2008, 2009; Salmon & Symons, 2004; Snitow, 1979).
This masculine greed for pornography is based on the fact that men want to have sex with greatest possible amount of women, without giving to much thought to the quality of these females. The greater the number of women a man can have sexual access to, more progeny will he leave, and it appears that no amount is enough. And the quantity and variety of the sexual female companions increases relative to the quality and extend of a male’s territory and its resources for future offspring. This is called territorial polygyny. In cultural terms, this is reduced to the fact that the more money a man has, the more women quantity and variety he will have access to. All this reinforces the fact that our species tends to be polygynyc (Low, 2001). As a matter of fact, this arrangement has been observed that in more than 80% of human cultures (Dunbar et al., 2011; Pinker, 2008, 2009). This is true even when the arrangement is monogamous in appearance. Many rich men tend to have sequentially monogamous relationships, divorcing frequently to get married with younger women than their actual one (Dunbar et al., 2011; Evans & Zarate, 2010).
All this, makes it more probable that a man will pay a woman to have sex with her and not the other way around. In the societies of hunters and gatherers, women openly ask for gifts to their lovers; generally, in form of meat. It can be concluded that women tend to be more faithful sexually speaking than men. But that doesn’t mean that women are 100% faithful, because otherwise we, men, wouldn’t have testicles bigger than those of gorillas. What does a woman get for being a little unfaithful? She can gain favors and gifts from their lovers, or, if sufficiently skillful to not get caught, she can mix good genes (brief relationships) with the possibility of obtaining good resources for her and her offspring from a rich man (long lasting relation) with the desire to give parental care (Pillsworth & Haselton, 2006).
In that way, both sexes use long-term (especially women) and short-term (especially men) mating strategies. When it comes to search for short-term relationships, men like women with an abundant sexual record, because they expect that the past repeats itself in the form of easy conquest. But when it comes to look for a long term relationship, men obviously prefer faithful and judicious women to minimize the risk of ending up giving resources to a baby that is not their biological son of daughter. This is called by Pinker (2009) the prostitute virgin dichotomy.
Regarding short-term relationships, women may watch the physical aspect of a man, but in general, the looks of a suitor is not the most important thing. The fact that the fertility of a man doesn’t decline with age as fast as it does in women is not a cultural bias. Rather it has to do with the fact that we men, except for a few cases of andropause, can be fertile since puberty to the rest of our lives. Hence by looking at the physical aspect, a woman won’t obtain much verifiable information about a man’s fertility.
Among other asymmetries already explained and given the fact that a woman cannot get rid of their children as easy as a man can do, women should be capable of distinguishing between a man that seeks for long-term relationship vs another one that looks for a short-term relationship. Women that couldn’t perceive this difference would run the risk of ending up as single mothers, which would decrease the probabilities that the offspring survival. That is talking about our ancestor’s prehistorical environment. Natural selection gave women several mental mechanisms to help her avoid this single mother destiny. Besides having the lying detection mental modules hypertrophied with respect to men, one of these mechanisms are the women’s dilatory tactics. Women tend to be more cautious than men when it comes to have sex. This waiting time allows a woman to, for example, extract material resources from the suitor to verify his commitment to her. This allows the woman to make sure that a man is interested in a long-term relationship and that he is not just seeking sex for a single night.
How did our ancestors solved the problem of selecting mates with “good” genes and avoiding those with “bad”genes? Indirect measuring forms evolved like the sensitivity of small differences in the physical appearance. For example, the more symmetrical a body is, in average, the better the genes of that individual should be, because symmetry is hard to achieve from a genetic point of view (Evans & Zarate, 2010).
If a woman solely looks for the capacity of a man to collaborate in the rearing of their children, she will guide her on cues that show how good is the candidate is obtaining resources, which in hunters-gatherers societies is measured mainly by the ability of a man to be a good hunter. In agricultural and industrialized societies this is reduced to how much wealth does the candidate have (Dunbar et al., 2011; Evans & Zarate, 2010). And although the following is highly modifiable by education, that is why women tend to be hypergamic according to (2004) or hypergynic agreeing to Dunbar et al. (2011).
In other words, women tend to look for men with a higher socio-economic-cultural status. The latter, summarized to the fact that women mature more and more rapidly especially from the social-intelligence point of view (Goleman, 2004; Joseph, 1996), has the consequence that women tend to seek for older men than them, with physical characteristics more developed, in which tallness is of high importance.
If these preferences evolved by natural selection, they must be universal for all cultures. Buss (1995) designed a questionnaire and gave it to more than 10,000 persons from 37 countries in six continents and five islands. The questions were answered by persons of societies that are monogamous and polygynyc, traditional and liberal, communist and capitalists. The results indicate that for both men and women, the intelligence, goodness and comprehension are very important. This study also showed that throughout the countries, men and women differ consistently in other criteria of mate choosing. Women value more the capacity to gain money than men; women assign a higher value to status, ambition and industriousness. And moreover they give a higher value to reliability and stability than men do. These results have been replicated several times (Pinker, 2008, 2009). It was found that women were not willing to go out or have sex with a man dressed with low level attire. But they were willing to consider all these relationships with a man dressed with high status clothing, even though it was the same man in all photos. The evolutionary prediction regarding feminine preferences for men with resources was confirmed. Like in the majority of studies about differences between men and women, the data obtained by Buss (1995) showed a big overlap in the scores of each sex. Nevertheless, the difference between the average masculine vs feminine scores were significant.
Men, universally prefer younger women. The evolutionary explanation to this fact is that fertility and reproductive potential is more related to age in women than in men. Feminine fertility touches a high point at the beginning of their 20s, declines after their 30s and absolutely ceases during menopause, which may have happened to stone age women in their 40s when diet was less nutritive. Because of this, men give much more value to signs of youth and beauty in a woman that the latter does with a man (Evans & Zarate, 2010). Is for all these things than we, men, are destined to become “green oldies” because while we grow old, our target age keeps being 20-year-old women. Anyway there are still many persons that think that beauty standards are entirely cultural artifacts. But in the last decades accumulated evidence show that there are many aesthetic preferences that are innate and universal.
Although these are universal tendencies, is obvious that they maybe, at least partially, modified by culture. Ages before to the present, all these physical cues were an indication of health, fertility and potential reproductiveness, but in our days, women have less babies, they have them at a more advance age, are better nourished and are less exposed to the harsh environmental conditions that our ancestral women from hunter-gatherers societies were exposed to in the far past. As a consequence of all these facts, current women may appear to be ancestral teenagers regarding beauty while the truth maybe that they are a little old. Besides all that, cosmetological and beauty industries can exaggerate these youth and fertility traits. Although the selection criteria on behalf of men are universal and hence they are not a conspiracy to oppress women like feminists argue, this doesn’t mean that the beauty industry is completely harmless. By constantly seeing beautiful people on the mass communication media, a recalibration of our preferences scale happens and may make us feel ugly, which obviously affects women more than men; and in extreme cases may lead to the development of psico-digestive disorders like anorexia and bulimia.
These physical beauty cues that men seek on women may be also related to the concept of neoteny, which in general terms refers to the retention of infantile characteristics on adults. We humans are neotenic chimpanzees that do not complete our development and we reproduce as juveniles. According to Desmond Morris (1995) we men are behaviorally neotenic (we behave like children) but physically we mature more than women. For the latter the contrary is the case. Women, behaviorally mature more and faster than men, but physically are more neotenic.
When a long-term partner is being searched, women as well as men seek for faithful companion. Nevertheless, jealously is different between sexes. The willingness to invest resources in the offspring by males is a preoccupation for women and that is why human females tend to be jealous about resources (Buss et al., 1992). Women are always sure that the son or daughter is of their own, and that is why the merely sexual infidelity doesn’t worry them so much. What women are really worried about is the emotional infidelity. The fear that her man has a female soul friend to which resources may be being deviated. On the contrary, we men show jealously regarding sex. For men sexual infidelity is much more grave than emotional one, because the risks for men are greater (Buss et al., 1992), in the way that a woman may end up being pregnant by another man, and the long term masculine partner may get in the situations of investing resources, time and energy in a child that doesn’t have his genes. Obviously no one likes that their partner has sex or is very affectionate to another person, but the reason changes according to the sex. Men don’t like that their women are affectious to another man because this may lead to sex. On the contrary, women don’t like their man to have sex with another woman because this can lead her man to get affectionate to his lover (Pinker, 2008, 2009).
Although it may sound trivial, one of the most successful ways that evolutionary psychologists use to examine the preferences when it comes to choose partners on humans, is by analyzing the classified ads published by persons who seek love companions. In general women that post those kinds of ads, are looking, above other things in men for: economic status and for willingness to invest significant time, energy and resources in a relationship. In the contrary, the ads published by lonely men show a strong inclination towards physical beauty in the women they are looking for (Dunbar et al., 2011). Men seek young and physical attractive women, and human females look for financial security, tallness and sincerity. Women do read the profiles of men’s ads. Men only look the photos. Moreover, women with high salaries, postgraduate studies and successful and prestigious careers, put even a higher value to their husband candidate’s status (Pinker, 2008, 2009).
Conclusions: The study of the mate selection tactics in humans is still in its infancy. We have focused in some of the more studied aspects. It must be pointed out that persons don’t fixate their attention on only one character to take decisions regarding the choosing of their companion, but base these preferences in a complex arrange of characteristics to take these decisions. We can get close to define some few key aspects that influence the mate choosing, but these decisions occur in a complex world in which de rivals exist and even more important, like any set of behaviors in humans, they are very influenced by culture.
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