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Introduction to Part IIMonique Borgerhoff Mulder a & Ulrich Mueller ba Department of Anthropology , University of California , Davis, CA, 95616, USA E-mail:b University of MarburgPublished online: 23 Aug 2010.

To cite this article: Monique Borgerhoff Mulder & Ulrich Mueller (2006) Introduction to Part II, Biodemography and SocialBiology, 53:3-4, 117-119, DOI: 10.1080/19485565.2006.9989121

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The Ecology of the Male Life Course

Introduction to Part II

Monique Borgerhoff Muldera,* and Ulrich Muellerb

aDepartment of Anthropology, University of California at Davis; bUniversity of Marburg

Evolutionary theory provides a frame-work within which the transitions indi-viduals make over their lifetime can bestudied from an adaptationist standpoint.Characteristics such as the weight atwhich babies are born, growth rates, ageat first reproduction, choice of mate (ormates), pace of fertility, investment oftime and resources into offspring, andrates of senescence can all be character-ized as life history traits. While there arespecies-specific averages for each trait,biologists have long appreciated thevariability both within and between pop-ulations. Indeed the discipline of humandemography focuses on this variability.The special contribution of the paperspublished here is to focus first on the lessstudied sex, and second to explore thevariability in life history traits underconsideration. The traits are adult size(Sear), marriage (Holland Jones and Fer-guson), the pace of reproduction andinvestment (Ravanera), and later lifehealth and mortality (Soneji, Grundy &Tomassini). This volume constitutes thesecond part of a special edition of SocialBiology Journal devoted to publishingthe proceedings of a seminar on theEcology of the Male Life Course, orga-nized by the IUSSP Scientific Panel

February 6, 2008.*Address correspondence to: Monique Borgerhoff

Mulder, Department of Anthropology, University ofCalifornia at Davis, CA 95616, USA. E-mail:mborgerhoffmulder@uc.davis.edu

Evolutionary Perspectives on Demogra-phy. The seminar was sponsored by theIUSSP and the University of Marburg,and was held at the Castle of Rauis-chholzhausen, German 10-12 October2006.

For men, large size, in terms of heightand body mass index, can be both advan-tageous for fertility and mortality out-comes, and costly. Accordingly acomplete evolutionary analysis of varia-tion in body size across populationsdepends on population-specific analysesof the effects of size on fitness outcomes.Rebecca Sears' analysis of data from arural Gambian population shows thatweight but not height is important formen's reproductive success, a patternthat parallels data from the !Kung butdiffers from western populations. Suchfindings undoubtedly reflect diseaseloads and thé seasonality of food avail-ability, and have possible implicationsfor variations in women's mate choicepatterns worldwide.

Variation in life history traits can bedriven by social as well as ecologicalfactors. In an analysis that examines maritalsex ratios, and by implications the con-straints on marriage formation, JamesHolland Jones and Brodie Fergusonreveal the relative shortage of men inColumbia, and how this varies acrossdepartments as a function of levels of vio-lence. The implication is that wherewomen are in excess, as for example in

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118 Borgerhoff Mulder and Mueller Social Biology

the one department where there are 160women for each 100 men entering themarriage market, women have little bar-gaining power in the marital contract, andmarriages degrade into consensual unionswith little paternal care, as is indeedoccurring in much of Columbia.

Zenaida Ravenera and colleagues'examination of the trajectory and timingof a whole series of life history decisionsmen must make, such as entry into work,leaving home, fathering children and"emptying the nest" reveal the complexi-ties of analyzing interdependent deci-sions. There are both cohort and socialstatus effects on the timing and sequenceof such events throughout 20th centuryCanada, which would appear to reflectnot only the constraints and opportunitiesafforded different individuals, but alsotheir ability to defy conventions andnorms, as demonstrated by the prevalenceof divorce and cohabitation among highstatus individuals. As recognized by theauthors state dependent dynamic model-ing is needed to analyze the varioustradeoffs among employment, family for-mation and dissolution, and parentalinvestment.

Life history allocations are rarelycheap. There is now considerable evi-dence demonstrating the costs of repro-duction in both sexes, but as EmilyGrundy and Cecilia Tomassini show, thepatterns are by no means uniform. Theirstudy of fatherhood in late 20th centuryEngland and Wales shows how in a lowfertility - low mortality population pater-nity itself is not deleterious to a man'slongevity nor to his later life health, eventhough very early fatherhood and largenumbers of children do precipitateadverse outcomes. Interestingly, whileevolutionary biologists emphasize thecosts of reproduction, demographers and

sociologists are revealing significant ben-efits, perhaps more apparent in the lessnutritionally- and disease-stressed popula-tions in which they generally work. Pursu-ing further the importance of socioeconomicfactors affecting longevity and later lifehealth Samir Soneji introduces innova-tive methodological techniques addressingsample selectivity to determine how ineq-uities based in race and gender affect laterlife health in "the oldest old". Suchapproaches will be key to determininghow the rate and nature of senescencevaries across and within populations.

To varying degrees each paper in thisvolume employs an evolutionary approachto the analysis of within and betweenpopulation variability in life history traits.Similarly each paper raises interestingquestions for subsequent analysis regard-ing tradeoffs among competing life his-tory expenditures. Linking the themes ofthe various contributions we might askhow male size in The Gambia affects laterlife health, and how this might change aseconomic development mutes seasonalvariations in food availability. How inColumbia might women balance the costsof being in a marriage squeeze with thebenefits of education and employment inthe female-dominated urban areas, andsimilar such tradeoffs for men? How dothe shifts in life history allocations overthe 20th century in Canada reflect changesin returns to education and employmentacross different socioeconomic groups,and how might these decisions also reflectshifts in the marital sex ratio contingenton education and employment opportuni-ties? Finally, with respect to later lifehealth and disability among the "oldestold" how might race, gender, parentingand socioeconomic status all interact toaffect outcomes? The power of an evolu-tionary approach is to provide a model in

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Vol. 53, Nos. 3-4 Introduction to Part II 119

which multiple variables can be examined consequence of differing constraints, oppor-within a single conceptual framework, with tunities and resources. Each of the papersspecific expectations for how trait values presented here provides a useful piece towill vary across and within populations as a this puzzle.

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