Fig. 4.2 Variance in (a) fertility and (b) reproductive success for Pimbwe men and women a

5 years of age, beyond which mortality is low), and number of spouses over the lifetime, categorized as 1, 2, 3, or more.

Among men and women who had completed their reproductive careers, only 3 (2.2%) men and 2 (1.3%) women had never married, indicating that marriage is virtually universal in this population. The mean values of fertility (men 8.41; women 8.17) and reproductive success (men 5.99; women 6.14) are not statistically different from each other, which suggests that there is no distortional sex bias to the sample. While men show greater variance in fertility (16.16) than women (11.34, Levene's test for equality of variances F = 5.87, p = 0.016, Fig. 4.2a), there is no significant difference in the variances in completed reproductive success (men 9.00; women 7.27, Levene's test F = 2.15, ns, Fig. 4.2b).

When fertility (Fig. 4.3a) and the numbers of offspring reaching 5 years of age (Fig. 4.3b) are shown in relation to number of spouses (1, 2 and 3 or more), an unexpected pattern emerges. Men fail to benefit in terms of fitness from multiple marriages, but women who marry three or more times produce more surviving children than do other women. Fertility and completed reproductive success are regressed on age, sex, and the number of spouses in a number of different models (Table 4.1a, b). Generally, across models, the number of spouses is negatively

Fig. 4.3 The associations between number of spouses and (a) fertility and (b) reproductive success for Pimbwe men and women. The mean is shown with a circle, and the standard error (*2) with a bar. For statistics see Table 4.1


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