Differences in Time Use for Mating and Nepotistic Effort as a Function of Male Attractiveness in Rural Belize David Waynforth Department of Anthropology, University of New Mexico, Albuquerque, New Mexico This paper explores whether physical attractiveness was a determinant of reproductive strategy in a sample of men living in rural Belize. A theoretical argument is presented to explain why differences in male physical attractiveness should lead to differences in strategy as evidenced by time-use, and why these differences should be especially apparent in nonindustrialized societies. Retrospective data were collected on men s time use during their last day off from work. The results were that more facially attractive men spent more time in mating effort and less time in nepotistic effort than less facially attractive men. Another component of physical attractiveness, fluctuating asymmetry, was not successful in predicting differences in time use. The results suggest that facially attractive men spend their leisure time seeking sexual access rather than spending it with kin, because their potential fitness returns are higher for this activity, whereas less attractive men receive higher returns to time spent with kin. This could be due directly to fitness returns to nepotism received by less attractive men, or because family involvement displays potential parental investment skills that are attractive to women. This may help build a reputation for reliability; in other words, time spent in nepotistic effort could be an alternative mating tactic that appeals to women s desire for a responsible paternally investing mate. 1999 Elsevier Science Inc. KEY WORDS: strategies. Time use; Fluctuating asymmetry; Facial attractiveness; Male reproductive Human males vary considerably in their propensity to continually seek new sex partners, and an evolutionary perspective can provide some insight as to why this variation exists. This research attempts to discover whether variation in male physical attractiveness, as a signal of phenotypic quality, is systematically associated with the tendency to spend time seeking Received April 27, 1998; revised September 9, 1998. Address reprint requests and correspondence to: David Waynforth, Department of Anthropology, University of New Mexico, Albuquerque, NM 87131, U.S.A. Evolution and Human Behavior 20: 19 28 (1999) 1999 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010 1090-5138/99/$ see front matter PII S1090-5138(98)00037-3
20 D. Waynforth new paternity versus nepotistic effort. The data used in this study come from a predominantly Mayan population in rural Belize. Male reproductive strategies primarily consist of two types of effort: mating effort and parental effort. Strategies can range from desiring to mate with as many females as possible while providing no parental investment, to absolute monogamy with high parental effort. Thus, there is a time-use tradeoff involved (mating vs. parental effort), which can be quantified if fitness is viewed as a function of two classes of time investment: investment in seeking new paternity and investment in existing kin. Strategy is measured in this research as differences in the amounts of time spent pursuing new paternity versus investment in kin. It can be argued that mating and parental effort may not always involve distinctly different activities as they are considered to be above. In fish species with male egg guarding, parenting behavior can, at the same time, act as enticement for additional females to mate with the male (Gross and Sargent 1985). It is also easy to see how displays of parenting ability in humans could have advertising value and help secure mating opportunities. For the purposes of the present study, such possibilities are ignored. This can be justified in that the vast majority of father child interaction observed or recorded in interviews took place in situations without any other observers present; thus, any advertising value that the parenting behavior might have had was lost. It additionally seems unlikely in the Mayan context that direct paternal care helps significantly in maintaining a marriage, because in the few cases in the data where women left their husbands, male parenting was not a primary reason for the breakup. This is also true of marital dissolution in at least one other traditional society, the Ache, where in 57 instances of female-initiated divorce not a single one was due to problems with male parenting (Hill and Hurtado 1996; 240). On top of this, it seems unlikely that women with husbands who heavily invest time into their children will, as a consequence, increase their copulation rate with their husband (sex for parenting) or refrain from seeking extra pair copulations, because extra pair copulations are assumed to be sought to produce children of higher genetic quality or increased genetic diversity than could be achieved with one husband. Physical attractiveness should be associated with male mating strategies in animals with male parental investment, as sexual and hence reproductive returns per unit of mating effort should, almost by definition, be higher for attractive males than for less attractive males, whereas rates of return for other activities are not as likely to vary with attractiveness. This prediction can be derived directly from the marginal-value theorem (Charnov 1976), because the returns to time spent in mating effort will diminish less rapidly for attractive males, and they therefore should spend more time in mating effort before switching activities. The effect may additionally be heightened if, as in barn swallows, the progeny of attractive males receive greater maternal investment (Møller 1994), which in turn would reduce the returns to paternal effort by attractive males. Evidence that the returns to mating effort are higher for attractive men can be found in data on attractiveness and lifetime sex partner number. Low fluctuating asymmetry, which is attractive to women (Gangestad et al. 1994), is associated with a greater number of lifetime sex partners in college undergraduates (Thornhill and
Male Attractiveness and Time Use 21 Gangestad 1994) and is marginally associated with greater sex partner number in this Mayan sample (Waynforth 1998). This may only reflect that more attractive men spend more time in mating effort, not that their actual returns are higher, but studies of female mate preferences for short-term sexual relationships show that physical attractiveness is more important to women in the short-term mating context (Buss and Schmitt 1993; Gangestad and Simpson 1990), which certainly suggests higher returns to time spent seeking copulations for attractive men. Studies of physical attractiveness and human mating strategies tend to be confined to college undergraduate samples. Thornhill and Gangestad (1993) have argued that preference for physically attractive mates evolved in part due to parasitedriven sexual selection, and that attractiveness acts as a readily observable signal of good health and good genes. This argument is supported by evidence that physical attractiveness is valued more highly in parasite-prevalent regions of the world (Gangestad 1993). The relatively pathogen-prevalent Belizean context used in the present research is thus particularly appropriate for the study of attractiveness and mating strategy. Two measures of physical attractiveness were used in this research: fluctuating asymmetry (FA) and female ratings of male facial attractiveness. FA is defined as deviation from perfect symmetry in the body s bilateral traits. High levels of asymmetry indicate that an individual has not been able to maintain symmetric development in the presence of genetic and environmental perturbations (Parsons 1990), and it is therefore a measure of phenotypic and genetic quality. FA has been shown to be associated with fitness in a wide variety of species, including humans. In human females, higher levels of breast asymmetry are associated with reduced fertility (Manning et al. 1996; Møller et al. 1995), and asymmetry in men is associated with fewer offspring fathered (Waynforth 1998). The second measure of attractiveness used is facial attractiveness as rated by female judges. This is a general measure of attractiveness, likely to include FA as well as other signals of attractiveness, such as deviation from averageness in facial features (Jones and Hill 1993). METHODS Subjects The study subjects were 56 men between the ages of 18 and 75 years, living in two neighboring villages in Western Belize. The villages, San Antonio and Cristo Rey, are accessible by an unpaved road that was built early in the 1980s. Before the road was built, access to the nearest sizable town (San Ignacio) was by canoe. This journey took about 20 minutes downstream from the closer of the two villages. Despite the relative ease of access to San Ignacio, up until the early 1990s some of the oldest individuals in San Antonio had never visited San Ignacio. Most younger men frequently leave the villages, and many commute by bus to work in other locations. The traditional mode of subsistence is slash-and-burn agriculture (known as milpa), although only 48% of the sample still engaged in milpa. The remainder per-
22 D. Waynforth formed paid work. The paid occupations represented varied from manual labor, such as logging and employment in large-scale agriculture, to work in the tourist industry and government work. Family life is very important to most of the men in the villages, and marital dissolution is rare by Western standards. Marriages recorded in the data were all monogamous, with a few men achieving serial monogamy. Informants often emphasized the importance of proving ability as a resource provider to a prospective bride s parents before marriage could take place. Couples whose relationships were disapproved of by their prospective inlaws occasionally eloped to other villages. Sometimes this was because they had little means of support, were too young, or the relationship would never be approved by either of the families. Marriages recorded in the data were not always stable. For example, in one case, a man eloped with his younger brother s wife. With the exception of events such as these, the family lives of the majority of the men studied appeared to be stable, and it was common to find that sons had set up households close to their parents and brothers, and maintained kin ties. The population of the two villages together totaled around 1500 individuals according to Belize 1991 census figures. Sixty-three percent of the men identified themselves as Yucateca or Mopan Maya. Of the remaining me, 34% were Mayan through one parent only or were Mestizo, and 3% belonged to other ethnic groups. Subjects were recruited by the following method: the villages were divided into groupings of approximately 10 houses based on geographic proximity, and then within each grouping of 10 houses one was selected. If no adult males were home, a time to return was arranged with other family members. If the man was not home at the arranged interview time, another house in the grouping was selected. This method yielded a total of 56 interviewed men, residing in every part of the two villages. Given that the sex ratio in Belize is 1.03 males to each female, and that 43% of the population is under 15 years of age (1997, CIA World Facts), this means that approximately 15% of the adult male population was sampled. Of the 58 men approached for interview, two refused to participate in the study. Interviews lasted between 1 and 3 hours, although sometimes considerably more time was spent with subjects than was taken to complete the interview. At the end of the interview, the subject was paid the equivalent of US $5. Variables Fluctuating asymmetry. To assess FA, eight bilaterally symmetric features were measured using 6-inch digital calipers: wrist breadth, elbow breadth, ear breadth, ear length, and finger length for four fingers. Left and right sides of these features were measured independently to the nearest millimeter. The FA of subjects was calculated by the absolute difference between left and right sides of each trait, divided by the mean trait size for the population, summed over all traits. In research involving FA, each trait is typically measured twice. However, for this research, a decision to only measure once was made because the first subjects measured were extremely uncomfortable with the process, and some coaxing was necessary to obtain the first set of measurements. An assessment of the ability of the
Male Attractiveness and Time Use 23 measurer can be made using previous FA data collected by the measurer in the United States, where data on 20 subjects and nine measures yielded an intraclass correlation of 0.68, F 5.19, p.002. This figure is very similar to those in other published studies (Furlow et al. 1998). An additional issue concerning FA data is that differences in asymmetry may contain a directional component. This is common in hand measurements and is due to handedness (Furlow et al. 1997). The Mayan sample did not, however, show significant deviations from zero for the mean on any of the hand measures used, but ear width was found to have a mean significantly different from zero (mean 0.088, T 3.31, p.002) and was not used in the FA calculations. It is difficult to envision why left ears should be wider than right ears, and this result is thus probably an artifact of sampling variation. Facial attractiveness. Facial photos were cropped to eliminate background and clothing, and were rated on a 1 to 10 scale for physical attractiveness by six male and six female judges. The judges were recruited from an introductory anthropology class at the University of New Mexico. This can be justified as there is consistent evidence that attractiveness ratings contain significant universal components and are not merely culture specific (Bernstein et al. 1982; Jones and Hill 1993; Maret 1983; Maret and Harling 1985; Thanakar and Iwakawi 1979). Use of raters in the United States rather than Mayans additionally provided assurance that ratings were not biased by other information that raters had about the subjects (San Antonio and Cristo Rey are small enough that everybody is acquainted with almost every other member of both villages). The judges provided moderately reliable ratings of attractiveness (Cronbach s alpha 0.64). Time spent with family and kin. The time-use data come from retrospective interviews. Although this is not the ideal method of collecting activity data and is often avoided by researchers, the method continues to be refined, as there is a continued need for retrospectively collected data (Berney and Blane 1997; Blane 1996). Because of this, it is often used in public health research and can provide reliable results (Grant et al. 1997; Harel et al. 1994; Parent et al. 1993). Subjects were asked to remember in detail the last day when they did not work, and recall their time spent in various activities and who they were with for the entire day in 1-hour blocks. They began by recalling time use during hours in which they were absolutely sure of their activity, then proceeded to fill in their activities for the remainder of the day. Some men had not recently taken a day off and were asked instead to recall their time use on the day in the past 2 weeks on which they did the least work. Subjects were never asked to recall activities that occurred more than 2 weeks prior to interview. Minimizing the time that passes between the event and recall of that event has been shown to significantly decrease recall bias (Harel et al. 1994). From this activity data, all of each subject s time spent with kin was summed. Family were defined as wives, siblings, parents, grandparents, and offspring. Cousins were not considered kin, because there appeared to be no definite taboo against marrying cousins, and some men (particularly Mopan-speaking Mayans) did not easily recognize cousins as a category of relatives. Time spent with wives was included as fam-
24 D. Waynforth ily time when other family members were present (see above argument), and as mating effort when the husband and wife were alone together. Time spent in mating effort. Using the time-use interview data, the sum of oneon-one time spent with wives, unrelated females, time spent in a mixed-sex group, and time spent with other males in any situation where they were likely to encounter women, was calculated. The definition of the last category may appear to be a little vague, but in practice, it was almost always easy to establish whether in individual instances encountering women was likely. For example, if two men spent time building a house it was not counted in this category, but if two men hung out at a village store where women go to shop it was counted. Relatively few men in the sample reported any one-on-one time with women other than their wives, or time in a mixed-sex group, but the three categories together provided enough data for meaningful statistical analysis as a binary response using logistic regression. Standard regression techniques were not used because the mode was zero, and the distribution was non-normal. The variable thus represents whether or not any time was spent in mating effort on men s last day off from work. This variable obviously captures time use that is not really mating effort. For example, it is impossible to tell whether two men out in public were actually engaging in mating effort. This measurement imprecision may obscure any relationship between attractiveness and time use, and will almost certainly cause an underestimate of the strength of the relationship. The few cases in which men simultaneously spent time with both kin and nonkin were counted in both time-use categories. These data are likely to be biased by intentional misrepresentation of sensitive time-use information even though anonymity was verbally assured at the beginning of each interview. Given that I had been present in each village for some time before interviewing began, I had established a rapport with several men who ended up in the sampling scheme. This prior contact with interviewees seemed likely to lead to increased disclosure of sensitive information from these men, and effects of this potential bias were examined by including prior contact as a binary control variable in analyses. This variable was scored as a one if I had 2 or more hours of prior one-onone contact with the subject (eight cases), or else was scored as a zero. RESULTS The correlation between FA and facial attractiveness was r.29 (p.12), which is slightly lower than the correlation observed in a sample of male undergraduates in the United States (Thornhill and Gangestad 1994). Table 1 displays the results of the analysis of time spent in nepotistic effort. All independent variables were entered simultaneously into the model predicting nepotistic effort. Martial status was, unsurprisingly, the single most powerful predictor of nepotistic effort. The other control variables, age, cash income in 1996, and whether or not I already knew the subject prior to interview were not significant in this model. Age was significantly correlated with more time with kin when entered as
Male Attractiveness and Time Use 25 the sole independent variable in a regression model predicting nepotistic effort, but was not significant when marital status was added to the model. Subjects who I already knew were not more likely to report less time spent with kin when this variable was entered as the sole independent variable in a regression model. Higher facial attractiveness rating was significantly associated with less time spent in nepotistic effort, but FA was not a significant predictor of time spent with kin either in the model shown in Table 1, or entered with any combination of the control variables. Figure 1 displays a scatter plot showing the relationship between facial attractiveness rating and number of hours spent with kin on men s last day off from work. Table 2 shows the results of a logistic regression model analyzing time spent in mating effort with all independent variables entered simultaneously. In this model the positive effect of my prior rapport with subjects was the most significant effect, meaning that men who I already knew reported more time spent in mating effort. Marital status showed a marginally significant negative association with mating effort, and, as in the previous analysis, its association with age caused age to drop out of significance in its presence. Income entered as the only independent variable in a regression model with mating effort, as the dependent variable was marginally positively associated with time spent in mating effort (beta 0.00016, p.097). Higher facial attractiveness rating was positively associated with mating effort, although the result was not quite significant at the 95% level (two-tailed). FA did not associate significantly with time spent in mating effort either in the model shown in Table 2 or entered with any combination of the independent variables shown. DISCUSSION Greater facial attractiveness proved to be a successful predictor of spending less time with kin and a marginally significant predictor of spending more time seeking access to women. This suggests that the fitness returns to mating effort were greater than the returns to time spent in nepotistic effort for facially attractive men and that the male time-use decisions are partly governed by differences in the returns to mating effort. FA was less successful at predicting time use. This is despite findings for this sample (Waynforth 1998) that females prefer men with low FA, because low FA is associated with more lifetime sex partners, earlier reproduction, and more offspring. Unfortunately, the success of FA as a predictor of early marriage and reproduction (Waynforth 1998) meant that very symmetric men were under-represented among unmarried men, who were more likely to be engaging in more mating effort and far Table 1. Results of Regression Model Analyzing Reports of Time Spent with Kin Predictor beta T p < Age 0.06 1.29.21 Knew subject 1.11 0.56.58 Marital status 5.97 3.33.003 Income 0.00 0.01.99 Facial attractiveness 2.66 2.56.02 Fluctuating asymmetry 21.74 1.55.13
26 D. Waynforth FIGURE 1. Time spent with kin as a function of the interviewee s facial attractiveness. Line is a least squares regression line. less nepotistic effort. The lack of significant findings here is therefore not surprising. What would ideally be required to avoid the sample bias associated with being unmarried found in these data would be to test whether symmetric men spend more time in mating effort and less in nepotistic effort in a sample of men who are too young to marry. It should, however, be the case that what little time married men are able to devote to mating effort should be associated with their FA, but it is not. For the married subsample using the independent variables to predict time spent in mating effort shown in Table 2 (except marital status). FA was not significantly associated with time spent in mating effort (estimate 6.33, 2 0.42, p.52). It is also interesting to note that low FA was more strongly associated with more one-onone time spent with women (which was one component of the mating effort variable) than with the weaker indicators, which together make up the mating effort variable (such as time spent in a group with women). This result is encouraging and suggests that more data or a more refined research design will reveal an association between FA and time spent in mating effort. As can be seen in Figure 1, although there was considerable variability in time spent with kin as a function of facial attractiveness, the most facially attractive men Table 2. Results of Logistic Regression Model Analyzing Time Spent in Mating Effort Predictor Estimate 2 p < Age 0.03 0.30.58 Knew subject 4.36 4.75.03 Marital status 3.50 3.18.08 Income 0.00 1.43.24 Facial attractiveness 1.95 3.64.06 Fluctuating asymmetry 4.87 0.15.70
Male Attractiveness and Time Use 27 spent about 9 hours less with kin than the most unattractive men. The magnitude of this difference is extremely surprising and deserves further attention. An obvious question to ask in regard to this is, what are the men who spend all day with kin doing? The data, along with personal observation, suggest that young unmarried men who spend their day off with kin are often at their parents home, doing chores. These chores usually involve tending the garden, cutting vegetation away from the house and garden, and building or repairing the house. For married men the activity pattern is the same, except that chores are being done around their own home. These chores are not trivial; for example, long grass around the home can harbor snakes and spiders capable of killing a child, or even an adult if a fer de lance is encountered. The remaining time at home is generally inactive, relaxation time. Attractive men tend to forgo this time in favor of activities performed away from kin, and more so if they are unmarried. This does not necessarily mean that chores are left undone, as they may be performed by other family members. The time-use differences associated with facial attractiveness suggest that extrapair copulations, premarital sex, and short-term relationships might be relatively easily attainable for attractive men, despite the stability of marital unions and apparently restrictive monogamous mating system. Lifetime sex partner data for the sample suggest that, although most men have few lifetime sex partners (the mean was 1.9, not adjusting for age, and the observed range was from 0 to 7), some are successful at having short-term relationships. The results shown here could also mean that attractive and unattractive men have different mate attraction tactics, with attractive men appearing in public and being more gregarious, and less attractive men proving family commitment and a high potential for providing paternal care by displaying family loyalty and hard work during their time off from work. This explanation seems particularly appropriate given the strong cultural emphasis on hard work and family loyalty. Financial support for this research was generously provided by Mr. and Mrs. K.F. Waynforth, Vard Johnson and Ruth Purtillo, and Paul and Loretta Burns. Substantial help with the research design and/or analysis was provided by Monique Borgerhoff Mulder, Martin Daly, Steven Gangestad, Kim Hill, Magdalena Hurtado, Randy Thornhill, Schuyler Waynforth, and Margo Wilson. REFERENCES Berney, L., and Blane, D. Collecting retrospective data: accuracy of recall after 50 years judged against historical records. Social Science and Medicine 45:1519 1525, 1997. Bernstein, I., Lin, T., and McClelland, P. Cross- and within-racial judgments of attractiveness. Perception and Psychophysics 32:495 503, 1982. Blane, D. Collecting retrospective data: development of a reliable method and a pilot study of its use. Social Science and Medicine 42:751 757, 1996. Buss, D., and Schmitt, D. Sexual strategies theory: an evolutionary perspective on human mating. Psychological Review 1:204 232, 1993. Charnov, E. Optimal foraging: the marginal value theorem. Theoretical Population Biology 9:129 136, 1976.
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