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Reproductive Constraints on Dominance Competition in Male Homo Sapiens
Reproductive Constraints on Dominance Competition in Male Homo Sapiens Ulrich Mueller Institute of Medical Sociology and Social Medicine, University of Marburg Medical School, Marburg, Germany
Allan Mazur Maxwell School, Syracuse University, Syracuse, New York
Dominance competition among males of the same group is characteristic for most primates including humans, with the outcome—rank—being positively associated with fitness. However, because we do not observe an evolutionary arms race toward hyperdominance in primate social systems, the evolution of ever more dominating behavior characteristics may be checked by increased costs in fitness to top rank. Empirical evidence for such costs, particularly in humans, however, is almost nonexistent. Here, for the first time, we can demonstrate for a cohort of male humans, military officers, all graduates of the class of 1950 of the U.S. Military Academy, constituting a closed and cohesive social group, that competitive qualities leading to top rank may have a negative effect on fitness. © 1998 Elsevier Science Inc. KEY WORDS: Male dominance; Reproductive contraints; Homo sapiens; Rank; Costs in fitness.
here are advantages to dominating conspecifics in competitive mating systems, including better access to desirable mates and to resources for raising offspring. Why, then, do such situations not lead to an evolutionary arms race in which individuals develop ever more dominating characteristics? Game theoretical models show how a frequency-dependent selection of different mating strategies may check this outcome (Maynard Smith 1982; Maynard Smith and Price 1973). However, almost no empirical studies suggest that attaining
T
Received March 20, 1997; revised May 31, 1998. Address reprint requests and correspondence to: Ulrich Mueller, University of Marburg Medical School, Institute of Medical Sociology and Social Medicine, 35033 Marburg, Germany. Evolution and Human Behavior 19: 387–396 (1998) 1998 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
1090-5138/98/$19.00 PII S1090-5138(98)00032-4
388
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top rank actually imposes a cost in fitness. In particular, there seems to be no such study in humans. Here we present the first example of reproductive constraints on high rank attainment in male Homo sapiens, based on lifetime professional and reproductive performances of 337 military officers, all graduates of the class of 1950 of the U.S. Military Academy at West Point. A general problem in applying evolutionary ecological reasoning to the study of modern human societies is that, here, social status cannot easily be equated with rank in dominance hierarchies, because the latter always reflects membership in various educational and professional groups with their own segmented marriage markets (Kalmijn 1991; Ultee and Luijkx 1990) as well as individual achievement within those groups. Moreover, it often cannot be inferred from achievement who will prevail in a competitive encounter. In the corps of professional military officers, however, difference in formal status corresponds highly with the inequality of giving and taking orders as well as with one’s chances of winning in competitive encounters. Also, orders have not only to be given, they have to be enforced. This is why, in the military, a dominant personality, of which facial dominance is an honest signal (Mueller and Mazur 1996, 1997), is a crucial component of the potential for high formal status, which also entails a higher income, and, in the U.S. military with its up-or-out career system, a longer time horizon of stable employment. Thus, among professional military officers, formal status can be better equated with rank in a dominance order than anywhere else in modern societies, and a cohort of West Point graduates who stayed in the military from their late teens to at least their late forties, living in a fairly closed social microcosmos constituting a nearly homogeneous marriage market, is thus an ideal sample for our purposes. Among these men, final military rank generally correlates positively with reproduction, but among topmost officers this relationship is reversed, with the highest generals having fewer offspring than lower ranked generals. A good case can be made that causality does not run from fitness to rank.
METHODS Data Data are taken from West Point’s graduation yearbook, The Howitzer (1950), and its annual Register of Graduates and Former Cadets, and from a survey mailed in 1990 to surviving members of the class, of whom 81% responded, including nearly all the generals. By this time the men, born between 1924 and 1929, had all completed their professional and reproductive careers (details in Mueller and Mazur 1996, 1997). At graduation, all men received the same rank, second lieutenant, and entered one of the army’s several branches or the air force. By 1960, 20% of the class had resigned for reasons uncorrelated with any variable considered here (Butler 1971a, 1971b). Nearly all of those who remained in the military through the 1950s would stay until 1970 (20 years) or longer in order to retire with benefits. Promotion to first lieutenant and captain is nearly automatic. Between 1960
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and 1969, about 75% of the men still on active duty graduated from a staff college, a prerequisite for promotion to colonel. Between 1962 and 1973, about one half of the staff college alumni graduated from a war college, a prerequisite for promotion to general. We confine our analysis to the 337 survey respondents who served 20 years or more in the military. Their distribution of final ranks is, in ascending order, major (1%), lieutenant colonel (26%), colonel (56%), brigadier general (7%), major general (5%), lieutenant general (3%), and “full” general (2%). Most men in the sample (98%) married and started to have children (96% of the ever-married) within a few years after graduation from the Academy. None of the 1,057 children born to our 337 men were born before 1950, and only 28 children were born after 1970. Thus, reproduction in most cases was completed well before retirement. Twenty-five men reported one deceased child, and five men reported two.
Variables Indicators of cognitive, social, and athletic competence at graduation were used to predict rank attainment and reproductive performance: GENERAL ORDER OF MERIT. At graduation from West Point, each man was assigned a number called his general order of merit (GOM) within the class, which was an overall evaluation combining academic grades, peer and instructor ratings of leadership and military aptitude, and physical education grades; the lower one’s GOM number, the better his evaluation. GOM is known to predict promotion into mid career (Butler 1976; Mazur and Mueller 1996; Mazur et al. 1984). FRIENDS. There is an approximately 50-word description of each graduating cadet in The Howitzer, typical of college yearbooks. As a crude measure of cadets’ sociability, the 41% of cadets whose descriptions made specific reference to their “friends” were indicated by a dummy variable called FRIENDS. ATHLETIC. By common standards, nearly all cadets are athletic and well proportioned physically, because these qualities influence admission to the Academy. The variable ATHLETIC was scored 1 if a man never participated on an intercollegiate team (36%); those on a team but not in their senior year (32%) were scored 2; those on senior year (varsity) teams (16%) were scored 3, unless they also won a letter, in which case they were scored 4 (13%). This variable measures not just athletic prowess but also competitiveness and ability to cooperate in teams. Football was the most prestigious sport at the Academy and is known to help a player’s military career (Atkinson 1989; Truscott 1978). Therefore, we created a variable called FOOTBALL, scored 2 for the seven lettermen on the varsity football team, 1 for the 11 other varsity football players, and 0 for the rest of the class. Wife’s birth year and education, husband’s birth year, death of wife, divorce, remarriage, and religious affiliation were checked as potential confounders. Independent variables and confounders were screened for correlations using gamma, which is insensitive to marginal distributions. Of course. FOOTBALL and ATHLETIC were correlated, as were birth years and religion of spouses, but otherwise there was no multicollinearity to complicate the interpretation of effects.
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RESULTS Career (1) GOM, ATHLETIC, FRIENDS, and FOOTBALL all predict success at various stages of the military career (details in Mazur and Mueller 1996; Mueller and Mazur 1996). Here we sum up z-standardized scores of GOM (multiplied by 21), FRIENDS, and ATHLETIC to form a composite measure (called POTENTIAL) of a man’s cognitive, physical, and social capabilities as shown at West Point. POTENTIAL and FOOTBALL both predict a man’s final rank as well as his completion of staff college and war college. (2) The career advantage of being a varsity football player is impressive. Of 337 cadets serving for 20 or more years, 17% were promoted to general, whereas 50% of varsity football players who remained in the military became generals. Five percent of the total sample made it to the very top as “full” or lieutenant generals, whereas 33% of the varsity football players reached this level. Three of the six “full” generals played on the varsity football team. (3) Multivariate analyses, either considering single transitions (promotions, graduations from staff and war college) with transition rate or logit models, or considering number of transitions still to be expected from various base ranks, confirmed these results. The higher the rank already attained, the more important FOOTBALL as compared to POTENTIAL became as a predictor of further achievement (not shown). No potential confounder affected these career transitions (Table 1).
Table 1. Final Rank, Staff College, and War College Outcome by Mean POTENTIAL Score and Mean FOOTBALL Score Final rank Major Lieutenant colonel Colonel Brigadier general Major general Lieutenant general General
Graduation Staff college (at risk: all men) No graduation Graduation War college (at risk: all staff college graduates) No graduation Graduation
Mean POTENTIAL score
Mean FOOTBALL score
2.877 2.648 .093 .351 .755 1.45 1.35
.000 .022 .060 .048 .125 .455 .667
Mean POTENTIAL score
Mean FOOTBALL score
2.525 .173
.060 .080
2.317 .433
.038 .128
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Reproduction (4) Professional success considerably influenced reproductive success. Generals had 3.67 children, compared to 3.02 for other officers (p , .001). Closer inspection reveals the difference in family size to be due to just one parity progression: generals were more likely than nongenerals to have a third child (.94 vs. .70 ; p , .0002). This difference remains if we break down nongenerals into war college graduates, staff college graduates, and others. Furthermore, total number of children, as well as having a third child, usually distinguishes winners from losers in the four major career transitions: to staff college, promotion to colonel (for staff college graduates only), to war college, and promotion to general (for war college graduates) ( p , .04; Table 2). (5) Generals also had more grandchildren than nongenerals at the time of our survey (3.17 vs. 2.68, p , .07). Both brigadier and major generals had more children (3.70 and 4.24, respectively) and more parity 3 progressions (.96 and 1.00, respectively) than the nongenerals. (6) However, lieutenant generals and “full” generals, the most successful men of the class, had fewer children (3.06 vs. 3.87, p , .03) and fewer grandchildren (3.00 vs. 3.27, ns) than brigadier and major generals, fewer parity 3 progressions (.87 vs. .98; p , .07), and fewer parity 4 and 5 progressions (.29 vs. .58; p , .03; .25 vs. .52; p , .15, respectively). These top-ranking generals had only about as many children and about the same parity progressions as nongenerals (colonels, lieutenant colonels, majors) (3.06 vs. 3.06 children; parity 3 progression: .87 vs. 70, ns; parity 4: .29 vs. 51, ns; parity 5: .25 vs. .47, ns). (7) We found no differential reproduction related to age at onset of reproduction, interbirth interval, or offspring survival and offspring maturation (here: age at first grandchild). We have no data on miscarriages, but childlessness or one-child families were distributed equally across ranks. Thus, we see no hint of a higher prevalence of reproductive failure among the highest ranking individuals. Instead, the factors shown to be powerful predictors of promotion, POTENTIAL and FOOTBALL, were negative predictors of reproductive performance within the group of generals only. A multivariate linear regression for log-transformed total number of children yielded for POTENTIAL: 2beta 20.325 (p 5 .054); for FOOTBALL: 20.047 (p 5 .79). A Cox regression for transition parity 3 progression yielded for Table 2.
Parity 3 Progression and Total Number of Children by Transition Outcome
Transition Staff college graduation (at risk: all men) Promotion to colonel (at risk: all staff college graduates without war college) War college graduation (at risk: all staff college graduates) Promotion to general (at risk: all war college graduates)
Outcome
Parity progression 3
No. of children
Not graduated Graduated Not promoted Promoted Not graduated Graduated Not promoted Promoted
.68 .75 .64 .72 .70 .80 .69 .94
3.04 3.12 3.12 2.98 3.01 3.22 2.92 3.65
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POTENTIAL: 2partial r 20.0625 (p 5 .69); for FOOTBALL: 2.339 (p 5 .028). In both instances, however, the significance levels would not survive the Bonferroni correction for number of tests, as appropriate. (8) The high generals had a considerably higher sex ratio among their offspring than low generals (32 sons and 20 daughters vs. 69 sons and 88 daughters, p , .02). This difference was independent of parity and family size. Also, whereas low generals had more grandchildren than high generals (3.22 vs. 3.00, ns), the number of grandchildren per child was higher among high generals than among low generals (0.96 vs. 0.82, ns)., which, however, is due first to the fact that high generals were about 6 months older than the other generals, and so were their children relative to the children of the other generals, by parity, and second to the much higher mean age of the fewer children of the high generals (33.25 vs. 31.01 years by the time of the survey, p , .10). Most of these children were still in the fertile period of their lives, so the younger are least likely to have completed their reproduction. Accordingly, once mean age of children is controlled, no effect of the type of general on the number of grandchildren per child could be observed in an OLS multivariate regression. Also, there was no difference in the sex ratio of grandchildren between the two classes of generals. (9) A closer inspection of the respondents family of origin (number of parents’ children and grandchildren, sex ratio among respondents siblings, first-born status) did not reveal anything noteworthy. Generals as a whole were slightly more likely to be first borns, but there was no such difference between top and other generals. In all other measures, no differences were found between generals and other officers, nor between top and other generals.
DISCUSSION (1) There can be no doubt that good records in cognitive, social, and athletic performance achieved as cadet, reflected in the measures POTENTIAL and FOOTBALL, aid rank attainment. (2) High rank predicts fitness: generals averaged 3.67 children compared to 3.02 children for others, and generals had a higher parity 3 progression and possibly higher parity 4 and 5 progressions. Also, those graduating from staff and war colleges had more children and a higher parity 3 progression than those who did not (Table 2). The parity 3 progression from second to third child is known to be the parity progression most sensitive to individual socioeconomic achievement in industrialized societies (Feeney and Lutz 1991; Kravdal 1992). Similar suggestions have been made for parity 4 and 5 progressions (Bumpass and Westoff 1970). Furthermore, generals were able to invest more in their children, who were more likely to graduate from college, and generals had more grandchildren than other classmen (3.17 vs. 2.68). Neither childlessness nor a one-child family affected career prospects at any rank, so it seems unlikely that professional success was an effect rather than a cause of above-average fecundity. Also, there is no relation between a wife’s birth year or education and her husband’s final rank or the reproductive performance
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of the couple. Catholic couples had more children, but religious affiliation did not predict any career variable. Thus, there is little room for explaining the correlation between career and reproduction by differences in marital behavior or in demographic or socioeconomic characteristics of spouses. We are left with the conclusion that professional success influenced reproductive performance. Attainment of the highest ranks came years after the fecundity transitions and therefore cannot have directly caused them. In the military as in many other occupational hierarchies, the sorting of men begins early. Perhaps after 5 or 10 years in service, the men who would eventually rise to the highest ranks had sufficient clues (evaluation records, prestige of assignments, encouragement by mentors) to correctly assess their prospects. From what is known about the dynamics of third and later births (Bumpass and Westoff 1970), we may speculate that couples in our sample decided to have two children as soon as possible, irrespective of the men’s military careers. Then, if prospects were bright, they opted for more children. The fact that waiting times before third, fourth, and fifth children were longer than before first and second children (not shown) may be seen as support for this speculation. (3) Nevertheless, the top achievers, the 17 “full” and lieutenant generals with the highest salaries and prestige, had lower fertility than the generals who were not quite as successful. Taking the generals as a separate group and checking the same potential confounders as were used for the whole sample yielded the same result: the correlation between rank and reproduction (now negative) cannot be explained by differences in marital behavior, demographics, or socioeconomic characteristics of their spouses. (4) It can be safely excluded that the true fertility of the high generals in sample exceeds the one of low generals because of an underreported illegitimate fertility excess of the former of more than 0.81 children per head. Respondents were explicitly asked to list all their biological (and legal) children by first name, vital dates, education, and profession. Illegitimacy in the white population of the U.S. (all men in the sample indicated a European ancestry) in 1950 to 1970 was low. Whereas high status gives men more chances for extrapair copulations (Pérusse 1995), there are no reports from modern Western societies indicating that high status is associated with an increased number of illegitimate children. (5) It also can be safely excluded that more successful nepotism by top generals can compensate for the difference in family size. It has been found repeatedly that, in the modern U.S. military, having a professional military officer as father may help one to get inside the system, but not any further (Butler 1971b; Janowitz 1971). In this sample, having a West Pointer as father or uncle was actually a negative predictor of making it to general (Mazur and Mueller 1996). Proportion of children with a college degree was about the same for both groups of generals. Remember also that top generals had about as many siblings and as many nieces and nephews as other generals. Other generals did have more grandchildren, and the lower grandchild-to-child ratio among low generals as compared with high generals probably will disappear once the children of the former have completed their reproduction. We therefore hold it unlikely that top generals could provide better procreation chances for their nieces and nephews or their grandchildren than other generals, if they were unable to do this for their children in the first place.
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(6) Also within the groups of generals, once the competitive performance indicators POTENTIAL and FOOTBALL were controlled, neither the total number of children nor parity 3 progression predicted career success. As we have noted repeatedly, POTENTIAL and FOOTBALL, which predict higher rank across the group of generals (except that “full” generals have lower POTENTIAL than lieutenant generals), also predict lower reproduction (Table 3), although these effects were not very strong or stable. However, because “full” and lieutenant generals had high average POTENTIAL and FOOTBALL scores, we can suggest cautiously that these high measures had some negative impact on reproduction, although the specific mechanism remains unclear. From the data it seems implausible that differences in reproductive success were caused by differences in men’s ability to produce offspring. It is more likely that these results reflect differences in conscious/unconscious decisions about allocation of investment in reproduction versus professional accomplishments, a difference in subjective tradeoff functions between maximizing professional success and maximizing reproductive success. (7) The high generals had a considerably higher sex ratio among their offspring than low generals, independent of parity and family size. This unexpected observation gave rise to two alternative explanations: (A) All future generals want to have (several) sons: those who are unlucky to have more daughters need more births to end at their desired number of sons, have to care for larger families, and, therefore, have a career handicap in relation to competitors who had more male offspring from the beginning. But if this were so, then the number of daughters should be a negative predictor and the sex ratio a positive predictor of professional success among generals, which was not the case. (B) Dominant personalities with a high testosterone level (Mazur and Booth 1998), who are set to rise to the top, have intercourse more frequently with their wives and, therefore, have more sons because of greater speed but lower survival of Y-chromosome sperm. But if this were so, measures of competitiveness such as FOOTBALL, as well as POTENTIAL, should predict number of sons or a
Table 3. Predictors of Total Number of Children and of Parity 3 Progression—Group of Generals Only OLS regression of log-transformed total number of children
POTENTIAL FOOTBALL
Beta
p
2.325 2.047
.054 .791 Cox regression for transition: parity 3 progression
POTENTIAL FOOTBALL
Partial r
p
2.063 2.339
.694 .028
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higher sex ratio, which was not the case. Also, the number of sons or sex ratio should predict final rank, which also was not the case. Thus, although the children of the high generals more often are male and are slightly older, they did not have a higher reproductive potential, compensating for the difference of 0.80 children in family size, which stands as it is: as a valid measure of lower fitness of the top achievers as compared to the second most successful achievers in this male dominance hierarchy, with the direction of causality going from differences in rank to differences in fitness, not vice versa. We have shown that (1) in the whole sample as well as in the group of generals, high rank is achieved by those with ever higher levels of relevant competitive traits (an exception being lower mean POTENTIAL in “full” than lieutenant generals); and (2) high status may cause above-average reproduction—a prerequisite for selection for traits that promote competitiveness for professional success. However, (3) the highest ranked generals had lower reproduction than lower-ranked generals— and about the same reproductive level as colonels. Because there are weak negative relations between indicators of competitiveness and fitness among generals, aboveaverage levels of competitive traits may depress reproduction. There are some parallels between these findings and the observations of Packer et al. (1995) (see also Dunbar 1995) of 138 free-ranging female baboons, who reported that high ranking females, despite enjoying shorter interbirth intervals and higher offspring survival rates than low-ranking females and offspring that matured earlier, nevertheless failed to have the highest lifetime reproductive success, because of a higher incidence of miscarriages (and possibly of later menarche and delayed first pregnancies) among females of higher rank. Packer et al. (1995) therefore suggest that “qualities essential to enhancing or maintaining . . . rank may also carry significant reproductive costs” (p. 63). Unfortunately, their findings are only correlational, unable to determine the direction of causality. Their data are compatible not only with high rank attainment causing decreased fitness but also with decreased fitness causing high rank attainment. In the latter case, there would not necessarily be selection against hyperdominant behavior.
CONCLUSION We conclude that the lower reproductive success of the highest ranking officers (lieutenant generals and “full” generals), compared to brigadier and major generals, results form high rank attainment and, therefore, possibly might indicate some selection against an extreme expression of characteristics that facilitate high rank attainment. The authors appreciate the cooperation of the men of the West Point Class of 1950 and the advice and support of Colonel (ret.) Morris J. Herbert, United States Military Academy, Association of Graduates; and the Office of Institutional Research, United States Military Academy. The research was funded by grant Mu609/5-1 from the Deutsche Forschungsgemeinschaft and by a grant from the Zentrum für Umfragen, Methoden und Analysen (ZUMA) in Mannheim, Germany, to the first author. We adopted two sentences in the Discussion from an anonymous reviewer because they captured so well what we wanted to say.
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REFERENCES Atkinson, R. The Long Gray Line. Boston: Houghton Mifflin, 1989. Bumpass, L.L., and Westoff, C.F. The Later Years of Childbearing. Princeton: Princeton University Press, 1970. Butler, R.P. Official Reasons for Separations from Active Duty of USMA Graduates from the Classes of 1942 through 1966. West Point, NY: Office of Institutional Research, U.S. Military Academy, 1971a. Butler, R.P. Survey of Careerists and Non-Careerists From the USMA Classes of 1963–1967. West Point, NY: Office of Institutional Research, U.S. Military Academy,1971b. Butler, R.P. Relationships between college performance and success as an army officer. Journal of Vocational Behavior 9: 385–391, 1976. Dunbar, R.I.M. The price of being at the top. Nature 373: 22–23, 1995. Feeney, G., and Lutz, W. Distributional analysis of period fertility. In Future Trends in Europe and North America. What can we assume today?, W. Lutz (Ed.). New York: Academic Press, 1991, pp. 169– 195. Janowitz, M. The Professional Soldier. New York: Free Press, 1971. Kalmijn, M. Shifting boundaries: Trends in religious and educational homogamy. American Sociological Review 56: 786–800, 1991. Kravdal, Ø. The emergence of a positive relation between education and third birth rates in norway with supportive evidence from the United States. Population Studies 46: 459–475, 1992. Maynard Smith, J. Evolution and the Theory of Games. Cambridge: Cambridge University Press, 1982. Maynard Smith, J., and Price, G.R. The logic of animal conflicts. Nature 246: 15–18, 1973. Mazur, A., and Booth, A. Testosterone and dominance in men. Behavioral and Brain Sciences 21: 353–397, 1998. Mazur, A., and Mueller, U. Channel modeling: from West Point cadet to general. Public Administration Review 56: 191–198, 1996. Mazur, A., Mazur, J., and Keating, C. Military rank attainment of a West Point class: effects of cadets’ physical features. American Journal of Sociology 90: 125–50, 1984. Mueller, U., and Mazur, A. Facial dominance in West Point cadets predicts military rank 201 years later. Social Forces 74: 823–850, 1996. Mueller, U., and Mazur, A. Facial dominance in Homo sapiens as honest signaling of male quality. Behavioral Ecology 8: 569–579, 1997. Packer, C., Collins, D.A., Sindimwo, A., and Goodall, J. Reproductive constraints on aggressive competition in female baboons. Nature 373: 60–63, 1995. Pérusse, D. Cultural and reproductive success in industrial societies: Testing the relationship at the proximate and ultimate levels. Behavioral and Brain Sciences 16: 267–322, 1995. Truscott IV, L. Dress Grey. New York: Fawcett Crest, 1978. Ultee, W., and Luijkx, R. Educational heterogamy and father-to-son occupational mobility in 23 industrial nations: general societal openness or compensatory strategies of reproduction. European Sociological Review 6: 125–149, 1990.
Allan Mazur Maxwell School, Syracuse University, Syracuse, New York
Dominance competition among males of the same group is characteristic for most primates including humans, with the outcome—rank—being positively associated with fitness. However, because we do not observe an evolutionary arms race toward hyperdominance in primate social systems, the evolution of ever more dominating behavior characteristics may be checked by increased costs in fitness to top rank. Empirical evidence for such costs, particularly in humans, however, is almost nonexistent. Here, for the first time, we can demonstrate for a cohort of male humans, military officers, all graduates of the class of 1950 of the U.S. Military Academy, constituting a closed and cohesive social group, that competitive qualities leading to top rank may have a negative effect on fitness. © 1998 Elsevier Science Inc. KEY WORDS: Male dominance; Reproductive contraints; Homo sapiens; Rank; Costs in fitness.
here are advantages to dominating conspecifics in competitive mating systems, including better access to desirable mates and to resources for raising offspring. Why, then, do such situations not lead to an evolutionary arms race in which individuals develop ever more dominating characteristics? Game theoretical models show how a frequency-dependent selection of different mating strategies may check this outcome (Maynard Smith 1982; Maynard Smith and Price 1973). However, almost no empirical studies suggest that attaining
T
Received March 20, 1997; revised May 31, 1998. Address reprint requests and correspondence to: Ulrich Mueller, University of Marburg Medical School, Institute of Medical Sociology and Social Medicine, 35033 Marburg, Germany. Evolution and Human Behavior 19: 387–396 (1998) 1998 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
1090-5138/98/$19.00 PII S1090-5138(98)00032-4
388
U. Mueller and A. Mazur
top rank actually imposes a cost in fitness. In particular, there seems to be no such study in humans. Here we present the first example of reproductive constraints on high rank attainment in male Homo sapiens, based on lifetime professional and reproductive performances of 337 military officers, all graduates of the class of 1950 of the U.S. Military Academy at West Point. A general problem in applying evolutionary ecological reasoning to the study of modern human societies is that, here, social status cannot easily be equated with rank in dominance hierarchies, because the latter always reflects membership in various educational and professional groups with their own segmented marriage markets (Kalmijn 1991; Ultee and Luijkx 1990) as well as individual achievement within those groups. Moreover, it often cannot be inferred from achievement who will prevail in a competitive encounter. In the corps of professional military officers, however, difference in formal status corresponds highly with the inequality of giving and taking orders as well as with one’s chances of winning in competitive encounters. Also, orders have not only to be given, they have to be enforced. This is why, in the military, a dominant personality, of which facial dominance is an honest signal (Mueller and Mazur 1996, 1997), is a crucial component of the potential for high formal status, which also entails a higher income, and, in the U.S. military with its up-or-out career system, a longer time horizon of stable employment. Thus, among professional military officers, formal status can be better equated with rank in a dominance order than anywhere else in modern societies, and a cohort of West Point graduates who stayed in the military from their late teens to at least their late forties, living in a fairly closed social microcosmos constituting a nearly homogeneous marriage market, is thus an ideal sample for our purposes. Among these men, final military rank generally correlates positively with reproduction, but among topmost officers this relationship is reversed, with the highest generals having fewer offspring than lower ranked generals. A good case can be made that causality does not run from fitness to rank.
METHODS Data Data are taken from West Point’s graduation yearbook, The Howitzer (1950), and its annual Register of Graduates and Former Cadets, and from a survey mailed in 1990 to surviving members of the class, of whom 81% responded, including nearly all the generals. By this time the men, born between 1924 and 1929, had all completed their professional and reproductive careers (details in Mueller and Mazur 1996, 1997). At graduation, all men received the same rank, second lieutenant, and entered one of the army’s several branches or the air force. By 1960, 20% of the class had resigned for reasons uncorrelated with any variable considered here (Butler 1971a, 1971b). Nearly all of those who remained in the military through the 1950s would stay until 1970 (20 years) or longer in order to retire with benefits. Promotion to first lieutenant and captain is nearly automatic. Between 1960
Reproductive Constraints on Dominance Competition
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and 1969, about 75% of the men still on active duty graduated from a staff college, a prerequisite for promotion to colonel. Between 1962 and 1973, about one half of the staff college alumni graduated from a war college, a prerequisite for promotion to general. We confine our analysis to the 337 survey respondents who served 20 years or more in the military. Their distribution of final ranks is, in ascending order, major (1%), lieutenant colonel (26%), colonel (56%), brigadier general (7%), major general (5%), lieutenant general (3%), and “full” general (2%). Most men in the sample (98%) married and started to have children (96% of the ever-married) within a few years after graduation from the Academy. None of the 1,057 children born to our 337 men were born before 1950, and only 28 children were born after 1970. Thus, reproduction in most cases was completed well before retirement. Twenty-five men reported one deceased child, and five men reported two.
Variables Indicators of cognitive, social, and athletic competence at graduation were used to predict rank attainment and reproductive performance: GENERAL ORDER OF MERIT. At graduation from West Point, each man was assigned a number called his general order of merit (GOM) within the class, which was an overall evaluation combining academic grades, peer and instructor ratings of leadership and military aptitude, and physical education grades; the lower one’s GOM number, the better his evaluation. GOM is known to predict promotion into mid career (Butler 1976; Mazur and Mueller 1996; Mazur et al. 1984). FRIENDS. There is an approximately 50-word description of each graduating cadet in The Howitzer, typical of college yearbooks. As a crude measure of cadets’ sociability, the 41% of cadets whose descriptions made specific reference to their “friends” were indicated by a dummy variable called FRIENDS. ATHLETIC. By common standards, nearly all cadets are athletic and well proportioned physically, because these qualities influence admission to the Academy. The variable ATHLETIC was scored 1 if a man never participated on an intercollegiate team (36%); those on a team but not in their senior year (32%) were scored 2; those on senior year (varsity) teams (16%) were scored 3, unless they also won a letter, in which case they were scored 4 (13%). This variable measures not just athletic prowess but also competitiveness and ability to cooperate in teams. Football was the most prestigious sport at the Academy and is known to help a player’s military career (Atkinson 1989; Truscott 1978). Therefore, we created a variable called FOOTBALL, scored 2 for the seven lettermen on the varsity football team, 1 for the 11 other varsity football players, and 0 for the rest of the class. Wife’s birth year and education, husband’s birth year, death of wife, divorce, remarriage, and religious affiliation were checked as potential confounders. Independent variables and confounders were screened for correlations using gamma, which is insensitive to marginal distributions. Of course. FOOTBALL and ATHLETIC were correlated, as were birth years and religion of spouses, but otherwise there was no multicollinearity to complicate the interpretation of effects.
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RESULTS Career (1) GOM, ATHLETIC, FRIENDS, and FOOTBALL all predict success at various stages of the military career (details in Mazur and Mueller 1996; Mueller and Mazur 1996). Here we sum up z-standardized scores of GOM (multiplied by 21), FRIENDS, and ATHLETIC to form a composite measure (called POTENTIAL) of a man’s cognitive, physical, and social capabilities as shown at West Point. POTENTIAL and FOOTBALL both predict a man’s final rank as well as his completion of staff college and war college. (2) The career advantage of being a varsity football player is impressive. Of 337 cadets serving for 20 or more years, 17% were promoted to general, whereas 50% of varsity football players who remained in the military became generals. Five percent of the total sample made it to the very top as “full” or lieutenant generals, whereas 33% of the varsity football players reached this level. Three of the six “full” generals played on the varsity football team. (3) Multivariate analyses, either considering single transitions (promotions, graduations from staff and war college) with transition rate or logit models, or considering number of transitions still to be expected from various base ranks, confirmed these results. The higher the rank already attained, the more important FOOTBALL as compared to POTENTIAL became as a predictor of further achievement (not shown). No potential confounder affected these career transitions (Table 1).
Table 1. Final Rank, Staff College, and War College Outcome by Mean POTENTIAL Score and Mean FOOTBALL Score Final rank Major Lieutenant colonel Colonel Brigadier general Major general Lieutenant general General
Graduation Staff college (at risk: all men) No graduation Graduation War college (at risk: all staff college graduates) No graduation Graduation
Mean POTENTIAL score
Mean FOOTBALL score
2.877 2.648 .093 .351 .755 1.45 1.35
.000 .022 .060 .048 .125 .455 .667
Mean POTENTIAL score
Mean FOOTBALL score
2.525 .173
.060 .080
2.317 .433
.038 .128
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Reproduction (4) Professional success considerably influenced reproductive success. Generals had 3.67 children, compared to 3.02 for other officers (p , .001). Closer inspection reveals the difference in family size to be due to just one parity progression: generals were more likely than nongenerals to have a third child (.94 vs. .70 ; p , .0002). This difference remains if we break down nongenerals into war college graduates, staff college graduates, and others. Furthermore, total number of children, as well as having a third child, usually distinguishes winners from losers in the four major career transitions: to staff college, promotion to colonel (for staff college graduates only), to war college, and promotion to general (for war college graduates) ( p , .04; Table 2). (5) Generals also had more grandchildren than nongenerals at the time of our survey (3.17 vs. 2.68, p , .07). Both brigadier and major generals had more children (3.70 and 4.24, respectively) and more parity 3 progressions (.96 and 1.00, respectively) than the nongenerals. (6) However, lieutenant generals and “full” generals, the most successful men of the class, had fewer children (3.06 vs. 3.87, p , .03) and fewer grandchildren (3.00 vs. 3.27, ns) than brigadier and major generals, fewer parity 3 progressions (.87 vs. .98; p , .07), and fewer parity 4 and 5 progressions (.29 vs. .58; p , .03; .25 vs. .52; p , .15, respectively). These top-ranking generals had only about as many children and about the same parity progressions as nongenerals (colonels, lieutenant colonels, majors) (3.06 vs. 3.06 children; parity 3 progression: .87 vs. 70, ns; parity 4: .29 vs. 51, ns; parity 5: .25 vs. .47, ns). (7) We found no differential reproduction related to age at onset of reproduction, interbirth interval, or offspring survival and offspring maturation (here: age at first grandchild). We have no data on miscarriages, but childlessness or one-child families were distributed equally across ranks. Thus, we see no hint of a higher prevalence of reproductive failure among the highest ranking individuals. Instead, the factors shown to be powerful predictors of promotion, POTENTIAL and FOOTBALL, were negative predictors of reproductive performance within the group of generals only. A multivariate linear regression for log-transformed total number of children yielded for POTENTIAL: 2beta 20.325 (p 5 .054); for FOOTBALL: 20.047 (p 5 .79). A Cox regression for transition parity 3 progression yielded for Table 2.
Parity 3 Progression and Total Number of Children by Transition Outcome
Transition Staff college graduation (at risk: all men) Promotion to colonel (at risk: all staff college graduates without war college) War college graduation (at risk: all staff college graduates) Promotion to general (at risk: all war college graduates)
Outcome
Parity progression 3
No. of children
Not graduated Graduated Not promoted Promoted Not graduated Graduated Not promoted Promoted
.68 .75 .64 .72 .70 .80 .69 .94
3.04 3.12 3.12 2.98 3.01 3.22 2.92 3.65
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POTENTIAL: 2partial r 20.0625 (p 5 .69); for FOOTBALL: 2.339 (p 5 .028). In both instances, however, the significance levels would not survive the Bonferroni correction for number of tests, as appropriate. (8) The high generals had a considerably higher sex ratio among their offspring than low generals (32 sons and 20 daughters vs. 69 sons and 88 daughters, p , .02). This difference was independent of parity and family size. Also, whereas low generals had more grandchildren than high generals (3.22 vs. 3.00, ns), the number of grandchildren per child was higher among high generals than among low generals (0.96 vs. 0.82, ns)., which, however, is due first to the fact that high generals were about 6 months older than the other generals, and so were their children relative to the children of the other generals, by parity, and second to the much higher mean age of the fewer children of the high generals (33.25 vs. 31.01 years by the time of the survey, p , .10). Most of these children were still in the fertile period of their lives, so the younger are least likely to have completed their reproduction. Accordingly, once mean age of children is controlled, no effect of the type of general on the number of grandchildren per child could be observed in an OLS multivariate regression. Also, there was no difference in the sex ratio of grandchildren between the two classes of generals. (9) A closer inspection of the respondents family of origin (number of parents’ children and grandchildren, sex ratio among respondents siblings, first-born status) did not reveal anything noteworthy. Generals as a whole were slightly more likely to be first borns, but there was no such difference between top and other generals. In all other measures, no differences were found between generals and other officers, nor between top and other generals.
DISCUSSION (1) There can be no doubt that good records in cognitive, social, and athletic performance achieved as cadet, reflected in the measures POTENTIAL and FOOTBALL, aid rank attainment. (2) High rank predicts fitness: generals averaged 3.67 children compared to 3.02 children for others, and generals had a higher parity 3 progression and possibly higher parity 4 and 5 progressions. Also, those graduating from staff and war colleges had more children and a higher parity 3 progression than those who did not (Table 2). The parity 3 progression from second to third child is known to be the parity progression most sensitive to individual socioeconomic achievement in industrialized societies (Feeney and Lutz 1991; Kravdal 1992). Similar suggestions have been made for parity 4 and 5 progressions (Bumpass and Westoff 1970). Furthermore, generals were able to invest more in their children, who were more likely to graduate from college, and generals had more grandchildren than other classmen (3.17 vs. 2.68). Neither childlessness nor a one-child family affected career prospects at any rank, so it seems unlikely that professional success was an effect rather than a cause of above-average fecundity. Also, there is no relation between a wife’s birth year or education and her husband’s final rank or the reproductive performance
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of the couple. Catholic couples had more children, but religious affiliation did not predict any career variable. Thus, there is little room for explaining the correlation between career and reproduction by differences in marital behavior or in demographic or socioeconomic characteristics of spouses. We are left with the conclusion that professional success influenced reproductive performance. Attainment of the highest ranks came years after the fecundity transitions and therefore cannot have directly caused them. In the military as in many other occupational hierarchies, the sorting of men begins early. Perhaps after 5 or 10 years in service, the men who would eventually rise to the highest ranks had sufficient clues (evaluation records, prestige of assignments, encouragement by mentors) to correctly assess their prospects. From what is known about the dynamics of third and later births (Bumpass and Westoff 1970), we may speculate that couples in our sample decided to have two children as soon as possible, irrespective of the men’s military careers. Then, if prospects were bright, they opted for more children. The fact that waiting times before third, fourth, and fifth children were longer than before first and second children (not shown) may be seen as support for this speculation. (3) Nevertheless, the top achievers, the 17 “full” and lieutenant generals with the highest salaries and prestige, had lower fertility than the generals who were not quite as successful. Taking the generals as a separate group and checking the same potential confounders as were used for the whole sample yielded the same result: the correlation between rank and reproduction (now negative) cannot be explained by differences in marital behavior, demographics, or socioeconomic characteristics of their spouses. (4) It can be safely excluded that the true fertility of the high generals in sample exceeds the one of low generals because of an underreported illegitimate fertility excess of the former of more than 0.81 children per head. Respondents were explicitly asked to list all their biological (and legal) children by first name, vital dates, education, and profession. Illegitimacy in the white population of the U.S. (all men in the sample indicated a European ancestry) in 1950 to 1970 was low. Whereas high status gives men more chances for extrapair copulations (Pérusse 1995), there are no reports from modern Western societies indicating that high status is associated with an increased number of illegitimate children. (5) It also can be safely excluded that more successful nepotism by top generals can compensate for the difference in family size. It has been found repeatedly that, in the modern U.S. military, having a professional military officer as father may help one to get inside the system, but not any further (Butler 1971b; Janowitz 1971). In this sample, having a West Pointer as father or uncle was actually a negative predictor of making it to general (Mazur and Mueller 1996). Proportion of children with a college degree was about the same for both groups of generals. Remember also that top generals had about as many siblings and as many nieces and nephews as other generals. Other generals did have more grandchildren, and the lower grandchild-to-child ratio among low generals as compared with high generals probably will disappear once the children of the former have completed their reproduction. We therefore hold it unlikely that top generals could provide better procreation chances for their nieces and nephews or their grandchildren than other generals, if they were unable to do this for their children in the first place.
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(6) Also within the groups of generals, once the competitive performance indicators POTENTIAL and FOOTBALL were controlled, neither the total number of children nor parity 3 progression predicted career success. As we have noted repeatedly, POTENTIAL and FOOTBALL, which predict higher rank across the group of generals (except that “full” generals have lower POTENTIAL than lieutenant generals), also predict lower reproduction (Table 3), although these effects were not very strong or stable. However, because “full” and lieutenant generals had high average POTENTIAL and FOOTBALL scores, we can suggest cautiously that these high measures had some negative impact on reproduction, although the specific mechanism remains unclear. From the data it seems implausible that differences in reproductive success were caused by differences in men’s ability to produce offspring. It is more likely that these results reflect differences in conscious/unconscious decisions about allocation of investment in reproduction versus professional accomplishments, a difference in subjective tradeoff functions between maximizing professional success and maximizing reproductive success. (7) The high generals had a considerably higher sex ratio among their offspring than low generals, independent of parity and family size. This unexpected observation gave rise to two alternative explanations: (A) All future generals want to have (several) sons: those who are unlucky to have more daughters need more births to end at their desired number of sons, have to care for larger families, and, therefore, have a career handicap in relation to competitors who had more male offspring from the beginning. But if this were so, then the number of daughters should be a negative predictor and the sex ratio a positive predictor of professional success among generals, which was not the case. (B) Dominant personalities with a high testosterone level (Mazur and Booth 1998), who are set to rise to the top, have intercourse more frequently with their wives and, therefore, have more sons because of greater speed but lower survival of Y-chromosome sperm. But if this were so, measures of competitiveness such as FOOTBALL, as well as POTENTIAL, should predict number of sons or a
Table 3. Predictors of Total Number of Children and of Parity 3 Progression—Group of Generals Only OLS regression of log-transformed total number of children
POTENTIAL FOOTBALL
Beta
p
2.325 2.047
.054 .791 Cox regression for transition: parity 3 progression
POTENTIAL FOOTBALL
Partial r
p
2.063 2.339
.694 .028
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higher sex ratio, which was not the case. Also, the number of sons or sex ratio should predict final rank, which also was not the case. Thus, although the children of the high generals more often are male and are slightly older, they did not have a higher reproductive potential, compensating for the difference of 0.80 children in family size, which stands as it is: as a valid measure of lower fitness of the top achievers as compared to the second most successful achievers in this male dominance hierarchy, with the direction of causality going from differences in rank to differences in fitness, not vice versa. We have shown that (1) in the whole sample as well as in the group of generals, high rank is achieved by those with ever higher levels of relevant competitive traits (an exception being lower mean POTENTIAL in “full” than lieutenant generals); and (2) high status may cause above-average reproduction—a prerequisite for selection for traits that promote competitiveness for professional success. However, (3) the highest ranked generals had lower reproduction than lower-ranked generals— and about the same reproductive level as colonels. Because there are weak negative relations between indicators of competitiveness and fitness among generals, aboveaverage levels of competitive traits may depress reproduction. There are some parallels between these findings and the observations of Packer et al. (1995) (see also Dunbar 1995) of 138 free-ranging female baboons, who reported that high ranking females, despite enjoying shorter interbirth intervals and higher offspring survival rates than low-ranking females and offspring that matured earlier, nevertheless failed to have the highest lifetime reproductive success, because of a higher incidence of miscarriages (and possibly of later menarche and delayed first pregnancies) among females of higher rank. Packer et al. (1995) therefore suggest that “qualities essential to enhancing or maintaining . . . rank may also carry significant reproductive costs” (p. 63). Unfortunately, their findings are only correlational, unable to determine the direction of causality. Their data are compatible not only with high rank attainment causing decreased fitness but also with decreased fitness causing high rank attainment. In the latter case, there would not necessarily be selection against hyperdominant behavior.
CONCLUSION We conclude that the lower reproductive success of the highest ranking officers (lieutenant generals and “full” generals), compared to brigadier and major generals, results form high rank attainment and, therefore, possibly might indicate some selection against an extreme expression of characteristics that facilitate high rank attainment. The authors appreciate the cooperation of the men of the West Point Class of 1950 and the advice and support of Colonel (ret.) Morris J. Herbert, United States Military Academy, Association of Graduates; and the Office of Institutional Research, United States Military Academy. The research was funded by grant Mu609/5-1 from the Deutsche Forschungsgemeinschaft and by a grant from the Zentrum für Umfragen, Methoden und Analysen (ZUMA) in Mannheim, Germany, to the first author. We adopted two sentences in the Discussion from an anonymous reviewer because they captured so well what we wanted to say.
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