The female choice

On the sexual attraction of women to different types of men during the menstrual cycle

Carmel Billo and Yosef Terkel Galileo

One of the issues that has occupied the human race since time immemorial is how the process of choosing a partner is carried out. In recent years, awareness of the importance of the subject of the monthly hormonal cycle in the study of female physiology and behavior has increased. Women demonstrate sexual behavior throughout the menstrual cycle, but hormonal changes during it affect the tendency to different and even polar objects of attraction.¹ This is how a phenomenon of two phases is depicted in the characteristics of sexual attraction: studies have revealed that compared to most of the cycle time (in the non-fertile period), then a preference for the "good breadwinner" is evident, around the time of ovulation an attraction to those with the "good genes" appears.

We will describe here the different faces of female sexuality during the menstrual cycle: how do hormonal changes affect women's tendency to different and even polar objects of attraction?

Two stages in sexual behavior: an evolutionary basis

In most mammalian species, ovarian hormones control the female's willingness to mate as well as her physical ability to mate. Female sexual behavior in mammals is controlled mainly by estradiol (a derivative of the hormone estrogen) and progesterone. There is a high correlation between an increase in estrogen levels and an increase in sexual behavior and between an increase in progesterone levels and a significant decrease in willingness to mate.

In primates, compared to most mammals, the ability to mate has been released from hormonal control and ovarian hormones mainly affect sexual motivation. The separation of the ability to mate from the interest to mate allows social experience and social context to influence the expressions of sexual behavior.

Females in monogamous species, such as porcupines and gibbon monkeys, tend to be more sexually active than necessary if the only function of mating is fertilization. Sometimes mating takes place even when fertilization is impossible or highly unlikely, and it may even occur during pregnancy. Even among invertebrates one can find examples of high sexual activity and multiple matings beyond what is required for fertilization in species where males assist females in the reproductive process.

These behaviors point to the possibility that there is an evolutionary preference for increased female sexuality as a means of manipulating male behavior: males tend to stay with females who are more sexually active and help them, responding not necessarily to direct physiological evidence of the female's fertility, but to a sign based on her behavior, which may sometimes be false.

Since different males differ in their ability to provide genetic benefit versus material benefit, it makes sense for the female to behave according to the changing needs during the cycle: the basis for looking for partners during the fertile phase (estrus phase) stems from reproductive considerations of obtaining a genetic advantage for the offspring.² At this stage, the considerations of choosing a partner are based on characteristics that indicate genetic quality such as facial features, body structure, voice, height, smell and behavior.

The continuous sexual behavior, i.e. the display of sexuality during the infertile stages of the cycle, stems from social-behavioral considerations of immediate return to the mother and the offspring. Among the female chimpanzees, it is possible to notice sexual activity and the initiation of matings to a greater extent specifically outside the period of peak fertility. Apparently the sexual behavior of the chimpanzees, living in groups, and mating during the non-fertile period, plays an important role in reducing the aggressiveness of males towards the offspring by disguising the identity of the father. On the other hand, at the peak of fertility, chimpanzee females mate with a smaller number of males, choosing those that offer a genetic benefit to the offspring.

In species where both parents take care of the offspring, the importance of mating outside the fertile days may help in understanding how evolution shaped human behavior and sexual psychology.

In various studies it was found that males with traits that indicate health and reproductive success are less willing for parental investment. Therefore, there is an advantage to the female who creates a monogamous relationship with a male who does not excel in these qualities, due to his willingness to provide support and material needs. In such a situation there is an advantage of receiving "better" genes from other males, while she receives help in parental care from the permanent male. Many species of monogamous birds, for example, are not necessarily sexually monogamous. In fact, about 15% of their offspring originate from mating outside of the permanent, monogamous couple relationship, a behavior known as EPC Extrapair Copulation)). This behavior allows the female to separate her choice of a genetic father from the choice of a partner for rearing the offspring and for the territory.

In humans, there were also reports of a peak in EPC around the time of ovulation, when women preferred men with characteristics that indicate inherited genetic advantages as "cheating" partners. However, women should be sensitive to the presence or absence of a stable and investing partner. Throughout most of human history, the price of pregnancy in the absence of support from a permanent partner in a long-term relationship was too high. In evolutionary terms, without the resources provided by an "investing" partner, the success of the mother's pregnancy and care of the offspring would have been considerably less.

Studies on contemporary hunter-gatherer populations show that the absence of the father has a distinct negative effect on the offspring's survival up to the age of 10. For example, the probability of death between the ages of 5-1 in the children of the Aché tribe in Paraguay is 2.6 times higher when the father dies than when both parents are present , and 2.9 times when the parents are divorced.

We can summarize and say that despite the importance of the monogamous framework, we can conclude that the various aspects of sexuality in the human female cycle were designed so that it would be possible to obtain a genetic advantage in the context of EPC, while utilizing the material resources provided by the permanent partner.

What is between a masculine face and the immune system

One of the characteristics of a face that is beautiful to us is relative symmetry. It is not about a symmetry that is absolute and artificial like a mirror. There are studies that show that there is even a preference for very slight asymmetry, such that you can't "put your finger on it", than for mirror symmetry. In general, symmetrical faces are more attractive faces, partly because they indicate health.

A distinct design of cheekbones, prominent eyebrow ridges and a large jaw are the signs of change in adolescent boys. This change in the facial features is related to the hormonal change in the man, which is mainly a change in the testosterone levels, which is responsible for the formation and expression of the secondary sex characteristics in males. But it was found that testosterone also has a negative effect on the immune system. Due to these two features, researchers hypothesized the immunocompetence handicap hypothesis.

Since testosterone is responsible for the formation of the secondary sex characteristics and their expression in males, this hypothesis suggests that at the same time it also has a negative effect on the immune system, and that the ability to express male characteristics comes at the price of a decrease in the function of the immune system and as a result the individual is more vulnerable to pathogens and parasites. Thus, only extremely strong, "high quality" males are able to "afford" to display prominent secondary sexual characteristics and survive despite the exposure to pathogens and parasites. Less resistant individuals cannot develop such markers without showing signs of damage during the normal course of development, damage that will be expressed in asymmetry in bilateral features. In various studies, a positive correlation was found between the survival of the offspring and the degree of expression of secondary male sex characteristics in their fathers, in a wide variety of animals.

Studies have also shown that men with high testosterone levels tend to invest less in a relationship and offspring. Being more attractive to women, they can prefer short and multiple sexual relationships over a stable relationship that requires material investment. In contrast, men with "feminine" facial features are rated in various preference tests as having character traits of positivity, honesty and good parenting.

A study of this type was conducted in 1999 at the University of St. Andrews in Scotland by Dr. Ian Penton-Voak (Penton-Voak) and colleagues, who processed with the help of a computer program clusters of male faces by extremizing all the facial features in male or female directions, while creating a sub-scale five degrees. For example, since a typical female jaw is smaller than a male jaw, feminization of a male jaw will be obtained by reducing it using the software (Figure 1). The pictures of the clusters were shown to women and their preference for facial features at different stages of the menstrual cycle and in relation to their marital status was examined (see: "Courters in Menstruation", "Galileo”36).

In accordance with the hypothesis of the principle of honoring the immune system, it was found in the photo rating studies that women are attracted to distinctly masculine features in the face such as prominent cheekbones and a large jaw, combined with bilateral symmetry, which together are associated with a high evaluation of dominance. This preference for testosterone-dependent traits is marked by a cyclical change, reflecting a change in progesterone levels. A positive relationship was found between high progesterone levels in the corpus luteum stage (the infertile stage, after ovulation), and between a preference for "feminine" and more delicate facial features in men. These are seen as reliable, warm and good parents. A negative relationship was found between high progesterone levels and a preference for male faces. Women show attraction to male facial features mainly on days 14-6 in the follicular phase (pre-ovulation) when the likelihood of conception is highest (Figure 2).

On top of that, women around the time of ovulation rated images of darker male faces as more pleasant. Skin color shows sexual dimorphism (differences between the sexes) in all human races, with men having darker skin on average than women. If so, a preference for dark skin during ovulation may also be considered an attraction to a distinctly masculine trait.

Voice pitch as a measure of masculinity

The male voice is one octave lower than the female voice. Voice pitch is the most prominent acoustic characteristic of human speech, exhibiting sexual dimorphism. The anatomy of the voice production system goes through memory (masculinization) under the influence of androgens (male sex hormones) during puberty, which cause the vocal cords of males to grow about 60% more than those of females. The frequency of the male voice is inversely related to testosterone levels during sexual development and adulthood. Since a low voice is dependent on testosterone (the level of testosterone and the volume of the vocal system are directly proportional), The low voice can mark a genetic quality according to the hypothesis of the principle of weighting of the immune system.

Indeed, women described a lower male voice as more attractive, and the degree to which they rated the man's voice as attractive was found to correspond to the ratio of the width of the man's shoulders to the width of his pelvis (the men with the lower voice also had more masculine physical characteristics, such as broad shoulders). These ratings even correctly predicted the reports on the number of partners the man had, and the number of times he was chosen as an EPC partner. In the issue of cyclical preference, the argument arises that a low voice is more attractive to women near peak fertility and predicts greater reproductive success. The selection of the female with "good" genes probably influenced the evolution of the male voice pitch; A low voice is preferred in a short-term sexual relationship more than in a long-term relationship.

The smell of the male body and the female orgasm

The sense of smell has a considerable influence on human sexual behavior. Substances discovered in human secretions act as sex pheromones, such as androstenes in male sweat. The body odor may indicate the physical condition of the potential partner and serve as a signal in the partner selection process.

It turns out that men rate visual information and smell as equal in importance, while women attribute greater importance to smell when choosing a partner. Likewise, male body odor preferences on the part of women maintain a cyclical pattern, when the smell of androstenone, which is a male sex pheromone, is more acceptable to women around the time of ovulation.

Women distinguish between "qualities" of different men towards the end of the follicular phase of the cycle (towards ovulation) unlike at other times. In a study conducted at the University of New Mexico, female students were allowed to smell 41 shirts worn by different men over two nights. It was found that women around the time of ovulation prefer the smell of shirts worn by symmetrical men.

Women on the non-fertile days did not show a clear preference for the scent of symmetrical or asymmetrical men. Developmental stability is expressed in the individual's ability to deal with genetic and environmental disturbances during development and eventually reach bilateral symmetry. Asymmetry is seen as a marker of developmental instability and predicts defects in traits such as health, fertility and longevity. On top of that, women are more likely to experience orgasm during intercourse with symmetrical men than with asymmetrical men.

The female orgasm plays an important role in saving the sperm and transporting it towards the uterus within the female reproductive system. An orgasm that occurs between one minute and 45 minutes from the moment of ejaculation, increases the volume of fluid retained in the woman's body from zero percentages up to approximately 65% ​​of the total fluid emitted in the emission. This allows the results of the sperm competition to be biased in favor of men with markers of "genetic quality" such as symmetry. If so, women need the ability to use a chemical signal in men's sweat to distinguish between those who have experienced and those who have not experienced developmental instability.

In an article published by Gangestad and Thornhill towards the end of the last century, it was suggested that the differences in smell may be due to differences in metabolism related to symmetry, such as the production of different amino acids in symmetrical men than in asymmetrical men, due to the symmetry of the production process. Another explanation for the difference in the body odor of symmetrical and asymmetrical men refers to the concentration and nature of skin bacteria, which contribute to body odor and vary as a function of developmental stability.

The tendency to betray the "good provider"

The attachment of women to partners with polar characteristics throughout the cycle stems from a structured conflict in reproductive interests. Due to the huge investment in raising a child to adulthood, women have developed a preference for partners who are capable and willing to provide resources for raising an offspring. However, at the same time, out of the benefit of selecting good genes, women developed an attraction to partners who display markers of genetic quality such as distinctly masculine characteristics and behavior and bilateral symmetry.

Although the woman desires both qualities - good genes and the ability to provide resources - it is difficult to find a partner who is endowed with both. Furthermore, to a certain extent there is a contradiction between them: the good genetic fathers are not necessarily the good caring fathers. It was found that men with high testosterone levels report high percentages of relationship instability, divorce and domestic violence.

It can be said that a woman has a biological interest in maneuvering between the two: attracting a "good breadwinner" as a long-term partner, and secretly looking for a "provider of good genes" by having a short sexual relationship with a secondary partner. Indeed, men who display markers of high fitness and high levels of symmetry are more often chosen as short-term partners than men who display less masculine traits and lower symmetry. It was found that among British women the frequency of EPC ("cheating") is 2.5 times higher towards the end of the follicular phase, towards ovulation, than during the last week of the cycle, during bleeding when fertility is low. This is while intercourse with the permanent partner tends to be evenly distributed throughout the cycle.

Women in the ancient past derived a genetic benefit from having sex that was not with their permanent partner, unless their permanent partner had "good genes" himself. If so, the selection should have shaped women's interest in men outside of the relationship, around the time of ovulation, depending on the characteristics of the permanent partner. That is, women who evaluate their permanent partner as having low genetic qualities, feel a greater urge to EPC as the time of ovulation approaches.

The degree of cyclical fluctuation of the female preference for opposite male traits is probably influenced by the level of estrogens and the attractiveness of the woman herself. "Masculine" women show greater volatility in attraction compared to "feminine" women, who show more moderate volatility. This is probably due to the ability of women who are perceived as particularly attractive to obtain long-term support even from men with high testosterone levels and distinctly masculine characteristics.

Cyclical fluctuations in the preference for men's facial features may also be influenced by the nature of the relationship the woman is seeking. In a sample of female undergraduates in England who were asked to choose a partner based on facial features, it was found that there is no cyclical change in the preference for long-term partners. On the other hand, in the preference for short-term partners, great cyclical volatility appeared.

The bipolar mating strategy has many risks due to the high cost to the permanent partner. The discovery of infidelity may lead to negative and even disastrous results for the woman. Therefore, in terms of the woman's interests, the behavior of EPC should be controlled by variables such as the likelihood of conception and the extent to which the permanent partner displays the markers for good genes.

1. The "menstrual cycle" refers here, as in any biological text, to the entire menstrual cycle, and not as a term describing the menstrual bleeding period. (the system)

2. The concept of estrus refers to the phase in the cycle of most female mammals, which precedes ovulation and in which the female is most suitable for mating. This is the fertile part of the cycle, starting in the middle of the follicular phase during which there is an increase in estrogen levels in the body. In the corpus luteum phase, after ovulation, progesterone levels exceed estrogen levels and the female is infertile.

Carmel spent She is an instructor at Sde Ein-Gadi School and at the Society for the Protection of Nature. Master's student in the Department of Zoology at the Faculty of Life Sciences at Tel Aviv University and researches the effect of melatonin on expressions of aggression and anxiety under the guidance of Prof. Nega Kronfeld-Shor.

Yosef Terkel He is a full professor at Tel Aviv University, in the Department of Zoology, specializing in animal behavior. In 1996, he established the "Animals and Society" unit, a unique academic unit within the university, which deals with the interrelationships between people and animals.