Extrinsic Mortality Effects on Reproductive Strategies in a Caribbean Community

Extrinsic mortality is a key influence on organisms’ life history strategies, especially on age at maturity. This historical longitudinal study of 125 women in rural Domenica examines effects of extrinsic mortality on human age at maturity and pace of reproduction. Extrinsic mortality is indicated by local population infant mortality rates during infancy and at maturity between the years 1925 and 2000. Extrinsic mortality shows effects on age at first birth and pace of reproduction among these women. Parish death records show huge historical variation in age-specific mortality rates. The infant mortality rate (IMR) in the early 1920s was low, increased dramatically beginning in 1929, and reached a maximum in the 1950s, at which point IMR declined steadily to its present low rate. The mortality rate early in life showed a quadratic association with age at first birth. Women who experienced conditions of low IMR early in life reproduced relatively late in life. Those born into moderately high levels of infant mortality tended to reproduce earlier than those born at low levels. At very high infant mortality levels early in life, women went on to delay reproduction until relatively late, possibly as a result of somatic depletion and energetic stress associated with the conditions that lead to high IMR. Population mortality rates at age of maturity also showed a quadratic association with age at first birth. The pace of reproduction, estimated as number of surviving offspring controlled for maternal age, showed a similar quadratic effect. There were complex interactions between population mortality rates in infancy and at maturity. When extrinsic mortality was high during infancy, extrinsic mortality later in life had little effect on timing of first birth. When extrinsic mortality was low to moderate in infancy, extrinsic mortality later in life had significant effects on adult reproduction. I speculate that these effects are mediated through development of personality facets associated with reproduction.