Variation in Age at First Birth
In developed societies, the period between the onset of reproductive maturity and age at first birth may be considerable, often regulated through birth control rather than restricted sexual activity. Average age at first birth in developed societies ranges from 25.1 years in the USA to 29.9 years in Canada (United Nations Economic Commission for Europe 2007). Teen motherhood is viewed as a public health concern and generally discouraged throughout the developed world. In contrast, in natural fertility societies (in which parous-specific fertility control does not occur), teen motherhood is the pervasive childbearing pattern, often encouraged and endorsed as a societal norm. The average age at first birth for a large sample of traditional societies, including forager, horticultural, and agricultural populations, ranges from 15.5 years among the Pume to 25.8 years among the Gainj (Fig. 5.1).
In natural fertility societies, a young woman’s exposure to conception is usually mediated through marriage rules. In some societies girls may marry prior to or shortly following menarche and give birth to their first child soon after reaching
Fig. 5.1 Cross-cultural average age at menarche (gray bars) and first birth (blue bars), sorted on age at menarche. *Societies on which the human norm of 19.5 is typically based. Sources: Data reported for all available traditional small-scale societies: Yanomama (Early and Peters 1990); Toba, Wichi (Valeggia and Ellison 2004); Puma (Kramer 2008); Aeta (Migliano et al. 2007); Hiwi, Tsimane, Walbiri, Efe, Hadza (Walker et al. 2006); Batak (Eder 1987); Maya (Kramer 2005); Ache (Hill and Hurtado 1996); Dobe Kung (Howell 2000 ); Agta (Early and Headland 1998); Gainj (Wood 1992) reproductive maturity. In other societies, girls may be sequestered, their fidelity closely guarded following menarche, with marriage and childbearing delayed for a period. In most cases, married women will live among close relatives throughout their lives and over the course of their reproductive career will bear 6-8 children, many of whom may not survive. Although women in traditional societies are not typically exposed to the lifestyle risks that can compromise teen pregnancy outcomes in developed societies, they tend to work physically hard for a living, may be food limited, and often have no access to prenatal health care.