Why do women have more children than they want? Understanding differences in women's ideal and actual family size in a natural fertility population

Abstract

Objectives We develop and test a conceptual model of factors influencing women’s ideal family size (IFS) in a natural fertility population, the Tsimane of Bolivia. The model posits affects of socioecology, reproductive history, maternal condition, and men’s IFS. We test three hypotheses for why women may exceed their IFS despite experiencing socioeconomic development: (H1) limited autonomy; (H2) improved maternal condition; and (H3) low returns on investments in embodied capital. Methods Women’s reproductive histories and prospective fertility data were collected from 2002 to 2008 (n = 305 women). Semistructured interviews were conducted with Tsimane women to study the perceived value of parental investment (n = 76). Multiple regression, t-tests, and analysis of variance (ANOVA) are used to test model predictions. Results Women’s IFS is predicted by their socioecology, reproductive history, maternal condition, and husband’s IFS. Hypotheses 2 and 3 are supported. Couples residing near town have smaller IFS (women = 3.75 ± 1.64; men = 3.87 ± 2.64) and less variance in IFS. However, the degree fertility exceeds IFS is inversely correlated with distance to town (Partial r = −0.189, df = 156, P = 0.018). Women living near town have greater maternal condition but 64% value traditional skills over formal schooling and 88% believe living in town is unfeasible. Conclusions While reduced IFS is evident with socioeconomic development, fertility decline may not immediately follow. When perceived benefits of investment in novel forms of embodied capital are low, and somatic wealth and large kin networks persist as important components of fitness, fertility may remain high and increase if maternal condition improves.

Modernization is associated with intensive breastfeeding patterns in the Bolivian Amazon

“…~80-500), ecology, and proximity to the town of San Borja (Gurven, 2012). Tsimane subsistence, household labor structure, and reproductive patterns have been described elsewhere (Gurven et al, 2009; McAllister et al, 2012; Winking & Gurven, 2011). …”

The evolved psychological mechanisms of fertility motivation: hunting for causation in a sea of correlation

“…However, preferences are strongly linked to intentions which, in turn, are associated with behaviours [111,[133][134][135][136][137][138].…”

“…Low female reproductive autonomy is associated with higher fertility [111]. One reason for this may be that women with low power within their relationship are less able to initiate contraceptive use [48].…”

What do men want? Re-examining whether men benefit from higher fertility than is optimal for women

“…We have reviewed the literature on sex differences in IFS and show in figure 1 that this discrepancy varies by world region (see the electronic supplementary material for sources used in this review). These sex differences in desired family size have been highlighted in the evolutionary literature [16,17,20] and are explicitly, or implicitly, interpreted as reflections of different fitness-optimizing strategies.…”

“…Thus, observations that women often report wanting fewer children than men do [7][8][9][10] and that cultural institutions that reduce women's reproductive autonomy (e.g. patrilocality, polygyny and patriarchal norms) are associated with higher fertility [11][12][13][14][15] have been interpreted as evidence that natural selection has favoured lower fertility, and specifically longer interbirth interval (IBI), reproductive strategies for women than for men [11,16,17]. Sexual conflicts of interest arise if males or females can pursue reproduction with more than one mate.…”