BIRTH INTERVAL AND THE SEX OF CHILDREN IN A TRADITIONAL AFRICAN POPULATION - AN EVOLUTIONARY ANALYSIS

Birth interval is a major determinant of rates of fertility, and is al so a measure of parental investment in a child. In this paper the leng th of the birth interval in a traditional African population is analys ed by sex of children. Birth intervals after the birth of a boy were s ignificantly longer than after the birth of a girl, indicating higher parental investment in boys. However, in women of high parity, this di fferential disappeared. Birth intervals for women with no son were sho rter than for those with at least one son. All these results are compa tible with an evolutionary analysis of reproductive decision-making. F irst born sons have particularly high reproductive success, daughters have average reproductive success and late born sons have low reproduc tive success. The birth interval follows a similar trend, suggesting t hat longer birth intervals represent higher maternal investment in chi ldren of high reproductive potential.