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In a previous post about "what women want," I provided a brief overview of what women prefer in a would-be husband, including a discussion of aspects of these preferences that are universal and others that vary from one context to the next. Here, I do the same for men’s preferences.

As I described in the previous post, parents or other kin typically decide who marries whom in most traditional contexts, thus placing constraints on men’s preference for one bride or another. My focus here is on men’s preferences in the absence of these constraints.

As most women have likely figured out for themselves, men are on average more enthusiastic about the prospect of uncommitted, casual and are more interested in sexual variety than are women. At a very basic level, these sex differences follow from the sex difference in investment in children and the sex difference in the cost-benefit trade-offs of .

As with all mammals, women pay a higher price than men should a pregnancy occur, and thus it is not surprising that they are more cautious than men when it comes to casual sex. This sex difference is somewhat smaller in liberal countries with readily available birth control, but even here, women are more cautious, on average, about casual sex than are men.

In any case, there are some species, such as California mice, in which males are monogamous and highly devoted to the female and their offspring, and other species, such as chimpanzees, in which males fight with one another for access to sexually receptive females and don’t form any type of long-term relationship with the female or their offspring. The chimpanzee pattern is common among mammals and is typically associated with larger males than females—this is a good indicator of male-male for females and dominant males that are polygynous. That is, these males have a lot of mates and don’t invest much in their offspring. Larger and physically stronger men than women (among many other things) fit this pattern, and it's likely the source of men’s interest in sexual variety, that is, an evolutionary history of polygyny (having several wives) and the reproductive benefits that polygynously married men enjoy.

This is not the whole story, however, because men’s mate preferences and investment in children is somewhere in between that found for California mice and chimpanzees. Although many men prefer casual sex and sexual variety in some situations, I’ve argued elsewhere that humans have a long evolutionary history of long-term relationships between males and females and male engagement with and protection of their offspring, similar to what we see in gorilla families.

So, sometimes it’s just about sex, but much of the time, men are looking for wives and will invest in the well-being of their children. However, the nature of marital relationships and men’s investment in their children varies across cultures. In contexts in which polygyny is not prohibited, men compete intensely (sometimes to the death) with one another for social influence and control of the resources (livestock, for example) needed to attract a wife or a second or third wife.

Marital relationships in these contexts are often described as aloof, and men’s investment in children is primarily through the resources they provide to their wives. These polygynous unions are generally restricted to the most successful men, and other men are monogamously married or single. But even monogamously married men in these societies are often looking for that second spouse rather than investing more in the current relationship and any associated children.

Given this, one of the most significant cultural influences on men’s mate preferences is the legal prohibition of polygyny. These are societies in which is socially-imposed, which reduces the intensity of male-male competition (e. ., violence declines) and shifts men’s focus from finding that next wife to investing in the current monogamous relationship and investing more in their children. This, of course, is a benefit to women who marry successful men (who otherwise would have another wife or two), but comes at a cost of more intense competition among them over these men. The competition is driven, in part, by the traits that desirable men prefer in a prospective bride. In other words, women enhance those traits that will grab the of desirable men and thereby give them an advantage over other women.

In these monogamous cultures, men and women are pretty similar in terms of the traits they are looking for in a spouse, such as and , but they weight one trait versus another differently. For instance, when making trade-offs between one potential spouse and another, one person might weight financial success, , and good looks as highly important, similar political views as moderately important, and housekeeping skills as unimportant. Another individual might value these same traits, but weight them very differently.

Although both men and women in monogamous societies prefer a marriage partner with traits (agreeable, ) that will facilitate a long, cooperative interpersonal relationship, they put different weightings on these traits, resulting in a different mix of preferences. Women rate interpersonal traits (e.g., agreeable) as more important than do men, and especially weight cultural success (e.g., income) or the prospect of success (e.g., ambition) more highly than do men, whereas men rate physical and age more highly than do women.

This is not to say that men’s attractiveness and women’s financial prospects are not important, but rather they are not as heavily weighted. There are also sex differences in the traits that are relationship dealbreakers (i.e., they lead to the termination of the relationship). Women have more dealbreakers than do men (i.e., poor financial prospects), but a partner’s low sex drive is a dealbreaker for more men than women.

The physical traits that might sway a man toward one prospective bride or another include facial and body attractiveness, as well as age. These preferences are why men are sometimes called more “visual” than women when it comes to deciding who is attractive and who is less so. From an evolutionary perspective, these traits make sense, because they are indicators of the woman’s health and the likelihood that she can have children.

Men are most attracted to women in their early 20s and with the following physical features: a waist-to-hip ratio (WHR) of about 0.7 (sometimes higher), facial features that signal a combination of sexual maturity but relative youth, proportionally longer legs, firm breasts, and small abdomen and waist. The key facial features seem to be large eyes, prominent cheekbones, and a large smile area, along with smooth and unblemished skin. It is not a coincidence that these are features that women enhance when they use cosmetics. For self-applied makeup, the average woman can move her perceived facial attractiveness from the 50th percentile to about the 60th percentile, and well beyond this with professionally applied makeup. Wearing high heels makes women’s legs look proportionately longer (among other things) and modestly to substantially increases their rated attractiveness.

Across cultures, there is modest agreement about which women (shown in photographs) have the most attractive faces and strong agreement regarding the least attractive ones, suggesting the most desirable facial features are influenced in part by local ideals of beauty. Nevertheless, men viewing attractive female faces (e.g., large eyes) show heightened activation of the brain’s built-in reward center (i.e., nucleus accumbens), as well as concurrent activation of other brain areas that are associated with reward-driven social behaviors and motivations, in keeping with some inherent contributions to these preferences.

Many men are also fascinated by women’s breasts. Women’s breasts are actually an interesting topic, because they are larger than they need to be outside of suckling, and thus they may be an indicator of maturity and fertility. Indeed, Havlíček and colleagues found that across cultures some men preferred average-size breasts, and others preferred larger breasts, but they all preferred women with firm breasts. The latter is correlated with age and the number of children the woman has had and should be a reliable indicator of the number of children she could potentially have in the future.

Women’s WHR, waist size, and body mass index (BMI)–a measure of leanness to independent of height–are all highly correlated and associated with rated attractiveness. In wealthy societies with socially imposed monogamy, men have a consistent preference for average to relatively slender women, but this is not a universal preference.

Across 62 cultures, Anderson and colleagues found that relatively slender women were preferred in 12 (19 percent) of them, whereas moderately heavy or “plump” women were preferred in 23 (37 percent) and 27 (44 percent) cultures, respectively. In subsistence populations, many women are slender due to poor , and those with higher body weight are considered to be more attractive and, in fact, have more children during their lifetime; in these contexts, WHRs between 0.7 and 0.9 are considered equally attractive. Basically, heavier women are preferred and considered beautiful in contexts in which the food supply is unreliable, and average weight to slender women are preferred in contexts in which food is readily available, and where lower-status women are heavier, on average, than higher-status ones.

Women’s age is a different matter, as men’s preference for relatively young women is found in wealthy nations with socially imposed monogamy and in traditional contexts. Why is age so important in men’s ratings of women’s attractiveness? It is simple: Men’s mate preferences evolved to be sensitive to indications of a woman’s age, because age and fertility are tightly linked in women. Women’s fertility is low in the teen years, peaks at about age 25, and then gradually declines to near zero by age 45. are less likely to become pregnant than are women in their 20s for any given sexual episode, and if they do become pregnant, they experience more complications than do women in their 20s. Risks begin to increase as women move into their 30s and increase sharply after age 35.

In all, men’s and women’s preferences for a prospective spouse are probably the most similar among wealthy and educated adults living in societies with socially imposed monogamy, where families live away from kin networks, men invest more in children than in many other contexts, and where the marital relationship is a more central aspect of their than it is in many other contexts. Even with these similarities, significant sex differences remain, with men’s greater focus on attractiveness and women’s greater focus on cultural success in a prospective spouse.