Researchers have explored the fitness consequences of female dominance hierarchies in many primate populations, with most studies highlighting differences in age of maturation, fertility, and offspring survival. We use resampling techniques and van Tienderen's (2000) elasticity path analysis to identify rank-related differences in finite rate of increase (λ) and their demographic correlates among segments of a semi-free-ranging rhesus macaque population. Higher-ranking population segments grew at greater rates for some portions of the 40-yr study period. The female members of these segments achieved these lifetime fitness differences through higher fertility and especially higher adult survival rates. This is the first clear evidence that social rank influences female primate adult survival, and is a crucial fitness component for any long-lived, slow-reproducing animal. Traditional methods of comparing lifespans, and other life history variables, among rank categories fail to identify most of the rank-related differences primarily because they require completed life histories that are available only on a small number of the females known in the population.

Trade-offs are central to life-history theory but difficult to document. Patterns of phenotypic and genetic correlations in rhesus macaques, Macaca mulatta —a long-lived, slow-reproducing primate—are used to test for a trade-off between female age of first reproduction and adult survival. A strong positive genetic correlation indicates that female macaques suffer reduced adult survival when they mature relatively early and implies primate senescence can be explained, in part, by antagonistic pleiotropy. Contrasts with a similar human study implicate the extension of parental effects to later ages as a potential mechanism for circumventing female life-history trade-offs in human evolution.

The genetics of primate life histories are poorly understood, but quantitative genetic patterns in other mammals suggest phenotypic differences among individuals early in life can be strongly affected by interactions with mothers or other caretakers. I used generalized linear mixed model extensions of complex pedigree quantitative genetic techniques to explore regression coefficients and variance components for infant and juvenile mortality rates across pre-reproductive age classes in the semi-free ranging Cayo Santiago rhesus macaques. Using a large set of records (max. n=977 mothers, 6240 offspring), strong maternal effects can be identified early in development but they rapidly “burn off” as offspring age and mothers become less consistent buffers from increasingly prominent environmental variation. The different ways behavioral ecologists and animal breeders have defined and studied maternal effects can be subsumed, and even blended, within the quantitative genetic framework. Regression coefficients identify loss of the mother, maternal age, and offspring age within their birth cohort as having significant maternal effects on offspring mortality, while variance components for maternal identity record significant maternal influence in the first month of life.

The patterning of quantitative genetic descriptions of genetic and residual variation for 15 skeletal and six life history traits was explored in a semi-free-ranging group of rhesus macaques (Macaca mulatta Zimmerman 1780). I tested theoretical predictions that explain the magnitude of genetic and residual variation as a result of 1. strength of a trait's association with evolutionary fitness, or 2. developmental and physiological relationships among traits. I found skeletal traits had higher heritabilities and lower coefficients of residual variation than more developmentally and physiologically dependent life history traits. Total lifetime fertility had a modest heritability (0.336) in this population, and traits with stronger correlations to fitness had larger amounts of residual variance. Censoring records of poorly-performing individuals on lifetime fertility and lifespan substantially reduced their heritabilities. These results support models for the fitness-related patterning of genetic variation based on developmental and physiological relationships among traits rather than the action of selection eroding variation.

The current study assessed the heritability of personality in a traditional natural-fertility population, the Ache of eastern Paraguay. Self-reports (n = 110) and other-reports (n = 66) on the commonly used Big Five Personality Inventory (i.e., extraversion, agreeableness, conscientiousness, neuroticism, openness) were collected. Self-reports did not support the Five Factor Model developed with Western samples, and did not correlate with other-reports for three of the five measured personality factors. Heritability was assessed using factors that were consistent across self- and other-reports and factors assessed using other-reports that showed reliabilities similar to those found in Western samples. Analyses of these items in combination with a multi-generation pedigree (n = 2,132) revealed heritability estimates similar to those found in most Western samples, although we were not able to separately estimate the influence of the common environment on these traits. We also assessed relations between personality and reproductive success (RS), allowing for a test of several mechanisms that might be maintaining heritable variation in personality. Phenotypic analyses, based largely on other-reports, revealed that extraverted men had higher RS than other men, but no other dimensions of personality predicted RS in either sex. Mothers with more agreeable children had more children, and parents mated assortatively on personality. Of the evolutionary processes proposed to maintain variation in personality, assortative mating, selective neutrality, and temporal variation in selection pressures received the most support. However, the current study does not rule out other processes affecting the evolution and maintenance of individual differences in human personality.