DIRECT AND CORRELATIVE PHENOTYPIC SELECTION ON LIFE-HISTORY TRAITS IN3 PREINDUSTRIAL HUMAN-POPULATIONS

Because natural selection acts simultaneously on several correlated tr aits, a single trait can be under both direct and correlative selectio n simultaneously. Correlative selection may either weaken or magnify t he association between a trait and fitness. Direct effect of a single trait on fitness can be assessed by removing the effects of correlativ e selection with multivariate techniques. We studied the phenotypic se lection on demographic life-history traits in three pre-industrial hum an populations, which experienced different mortality environments. We used path-analysis to estimate direct and correlative selection on di fferent traits in females and males. Our results indicate substantial differences among the sexes in the force of phenotypic selection on ke y life-history traits. For females, the most important component of re productive success was the age at first reproduction. Most important c omponent of fitness for males was the quality of mate. In addition, ou r analysis revealed considerable among-population variation in the sel ection on life-history traits. These differences are in accord with th e historical notes of among-population variation in the lifestyle and harshness of the environment, suggesting that among-population variati on in life-history traits may have been a response to the environmenta l variation.