Evolutionary hypotheses for human childhood

Abstract

The origins of human childhood have fascinated scholars from many disciplines. Some researchers argue that childhood, and many other human characteristics, evolved by heterochrony, an evolutionary process that alters the timing of growth stages from ancestors to their descendants. Other scholars argue against heterochrony, but so far have not offered a well-developed alternative hypothesis. This essay presents such an alternative. Childhood is defined as a unique developmental stage of humans. Childhood is the period following infancy, when the youngster is weaned from nursing but still depends on older people for feeding and protection. The biological constraints of childhood, which include an immature dentition, a small digestive system, and a calorie-demanding brain that is both relatively large and growing rapidly, necessitate the care and feeding that older individuals must provide. Evidence is presented that childhood evolved as a new stage hominid life history, first appearing, perhaps, during the time of Homo habilis. The value of childhood is often ascribed to learning many aspects of human culture. It is certainly true that childhood provides “extra” time for brain development and learning. However, the initial selective value of childhood may be more closely related to parental strategies to increase reproductive success. Childhood allows a woman to give birth to new offspring and provide care for existing dependent young. Understanding the nature of childhood helps to explain why humans have lengthy development and low fertility, but greater reproductive success than any other species. Yrbk Phys Anthropol 40:63–89, 1997. © 1997 Wiley-Liss, Inc.