In an article entitled "Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures," David M. Buss delineates a study he conducted to determine if there are certain characteristics that males and females tend to look for in a possible mate. Based on physiological differences and the stereotypical role of each sex, he hypothesized that there would be a number of characteristics that are considered more important to one sex or the other. Culture and environment, however, greatly influence our perceptions of the characteristics that embody a "desirable mate." David Buss discovered that there were no studies on sex differences in human mate preferences that transcended cultural differences, so he distributed questionnaires to people of differing socioeconomic backgrounds from thirty-seven different cultures. From their responses, he attempted to determine the extent that our innate instincts, rather than cultural influences, affect our preferences in potential mates.

Based on prior research, Buss speculated that the largest differences between the sexes on mate preferences would be found in earning capacity, ambition-industriousness, youth, physical attractiveness, and chastity. In his article, Buss outlines several reasons why he chose these five characteristics. First, parental investment in one's offspring should influence decisions in choosing mates. Simply by the nature of mammalian reproduction, females are investing more time and energy in the consequences of sexual intercourse. (Female humans carry the child for nine months before giving birth to a completely helpless baby. At the same time, male humans can choose whether or not to invest any time and energy into raising the child.) By virtue of their reproductive roles, the female usually acts as caretaker, while the male -- if he chooses to participate -- acts as resource provider. Given these roles, it seems that females would value characteristics that point toward a mate who will provide good resources for her and her offspring. In humans, "resources" typically come from job earnings so it is likely that females look for earning capacity and other characteristics that complement earning capacity, such as ambition-industriousness.

Second, fertility and reproductive value help determine which characteristics are favorable in potential mates. Both sexes seek potential mates who have the ability to reproduce. While males have the ability to do their part for most of a life-span, females are more limited by age. Because of this difference, it seems likely that males will place more importance than females on characteristics that point toward good reproductive abilities, such as youth and beauty. There are two ways to characterize reproductive abilities: reproductive value and fertility. Reproductive value refers to "expected future reproduction," usually translated into years of successful reproduction for the future. Fertility is the "probability of present reproduction." Peak reproductive value for humans occurs at the onset of puberty, while female fertility peaks in the mid-twenties. Depending on whether a male is seeking a long or short-term mating partner, Buss speculates that he will value either reproductive value or fertility in potential mates. Both reproductive value and fertility are dependent on health and youthfulness, which can be estimated through physical and behavioral attributes. According to this theory, males should value youth and beauty more than females.

Third, paternity probability should play a role in determining which characteristics men find favorable in women. For species in which males invest in their offspring, it is important for males to know that they are investing in their own and not someone else's offspring. For this reason, it seems that males should value chastity in potential mates. Additionally, Buss speculates that females will also value chastity if it ensures that her mate will invest in her offspring and not someone else's. However, Buss hypothesizes that results will show chastity as being more important for males than for females in the search for potential mates.

Buss, with the help of three translators for each of the non-English-speaking countries, distributed a questionnaire to more than ten thousand participants. The questionnaire consisted of three parts. The first part asked for the participant's biographical data such as age, sex, religion, and number of siblings. The second part asked for the participant's ideal age of marriage for his or her own sex, the preferred age difference between the self and the partner, and who (self or spouse) the participant preferred to be older. The third part asked participants to rate eighteen characteristics on how desirable each of them would be in a mate.

Although there were wide-ranging individual responses, the averaged responses were consistent with four out of five of Buss's hypotheses. Thirty-six of the thirty-seven samples show females valuing "earning potential" more than males. Thirty-four out of thirty-seven samples demonstrate females placing more importance on "ambition-industriousness" than males. All thirty-seven samples show males preferring mates younger than themselves and females preferring mates older than themselves. All thirty-seven samples show males preferring "good looks" more than females, but only thirty-four of those samples show a significant difference between the two sexes. Only twenty-three of the thirty-seven samples show males preferring chastity more than females.

For the most part, the results from each individual culture are quite congruous with results from the other cultures. However, there are several countries that differ from the average on certain characteristics and Buss offers some interesting hypotheses to account for these differences. For example, Colombian, Spanish, and South African Zulu participants show that males value ambition-industriousness more than females. The only sample that significantly deviated from the average was the Zulu tribe. According to one of Buss's research collaborators, physically demanding tasks such as building the house and fetching water are considered women's work in the Zulu culture. While the females are doing these jobs, men usually travel to urban centers to find work. Buss speculates that these social norms may account for the deviation from the average of other countries. Another interesting correlation Buss makes between a country's social norms and its deviation from preferences seen in many other countries has to do with preferred age difference. Nigeria and Zambia are the only two countries who practice polygamy that participated in Buss's questionnaire, and they are also the two countries in which the males have the highest preferred age difference between themselves and their spouses. This can be attributed to the fact that the typical male in a polygamous society is generally older than his counterpart in a monogamous society.

Though Buss's experiment gives readers some very interesting results, there are some faults with his conclusions. Readers should be aware that it is not uncommon for researchers to convey their results in a way that can be somewhat misleading. For instance, Buss reports that males prefer younger mates while females prefer older mates. The way the questionnaire was set up, however, did not leave them the option to be indifferent on this subject. Most likely there were participants who are indifferent to a few years of age difference in potential mates. Because these indifferent participants had to choose either older or younger mates, they probably followed the social norm, choosing younger female mates and older male mates. Participants' lack of choice makes the conclusion that females prefer older mates and males prefer younger mates questionable. The only piece of evidence to redeem this conclusion is that, on average, the male participants are older than their real-life spouses while female participants are younger.

Another somewhat questionable, but interesting conclusion Buss draws is that males prefer fertility to reproductive value. He makes this conclusion based on male subjects' age of marriage and the age difference between themselves and their spouses. Buss found that, in general, these male subjects marry women in their mid-twenties, which is the female's peak fertility point, rather than girls just entering puberty. This conclusion is not valid for a couple of reasons. First of all, in first-world countries, such as the U.S. and western European states, it is not feasible for teenage girls to get married. It is not legal for older males to marry teenage girls in many situations. In addition, teenage girls have other responsibilities, such as getting an education, that do not complement the demands of reproducing and raising children. Second of all, if males prefer fertility to reproductive value, wouldn't we see fairly consistent marriage ages throughout history? Instead, when we compare marriage ages in the 1990's with those of merely a century earlier, we will see quite a difference. In general, women are getting married at older ages than they did a century ago. Does this mean that in the last hundred years men have switched from preferring reproductive value to fertility? A more likely explanation, however, is that social norms have changed and people have changed their preferred age of marriage to accommodate these social norms.

Despite some of his questionable conclusions, which are almost inevitable in any psychology experiment, Buss does provide interesting results. The more researchers study, the more it seems that nearly every human decision and behavior is related to an evolutionary struggle to survive and pass on one's genes. I wonder, though, how much these preferred mate characteristics, which Buss attributes to our innate desire to reproduce successfully, will change as sex roles change. Females will always carry the child for nine months, thus, females will always have more initial investment than males, and males will always place more value than females on characteristics that imply high fertility or reproductive value. However, the male's role as the "resource provider" may change, thus changing the female preferences for earning capacity and ambition-industriousness that result from stereotypical roles. In the future, perhaps we will see less of a gap between the sexes in preferred mate characteristics. These preference changes, however, will not negate the role of evolution in our choice of mates -- preferred mate characteristics will continue to reflect evolutionary adaptations as well as the socially accepted norms for the time period.