Examining the terminal investment hypothesis in humans and chimpanzees: Associations among maternal age, parity, and birth weight

Abstract

The terminal investment hypothesis (Williams [1966] Adaptation and Natural Selection; Princeton, NJ: Princeton University Press) holds that reproductive effort should increase over time in iteroparous species in which reproductive value declines with age. Attempts to model this hypothesis and test it in various species have produced mixed results. Clutton-Brock ([ 1984] Am. Nat. 123:212-229) argued that simply testing for changes in propagule size with age fails to recognize that the costs of producing offspring of a given size may increase over the lifespan, hence absence of a positive correlation does not defeat the hypothesis. However, this interpretation is weakened by evidence of sequential increases in propagule size independent of age, as such changes reveal a capacity to increase absolute investment over time. Humans and chimpanzees meet the preconditions of the terminal investment hypothesis. Surveying the obstetrics literature, we show that the majority of published studies indicate that parity has a positive effect on birth weight, but age has no effect. Analyzing 436 captive chimpanzee births, we document a positive influence of parity and a negative influence of age. We therefore conclude that, though it is yet to be replaced by a more compelling alternative, the terminal investment hypothesis is not supported in these two species, as absence of a positive effect of age on birth weight cannot be interpreted in a manner congruent with the hypothesis.

Mount Pinatubo, Inflammatory Cytokines, and the Immunological Ecology of Aeta Hunter-Gatherers

“…Such data, if representative, are consistent with reports of unusually long interbirth intervals (35 months) among the Aeta (Gawlik et al 2011), but not with the correlation between higher birth orders and shorter interbirth intervals among the Agta (Goodman et al 1985). Extended nursing by older Aeta mothers could be a means of suppressing ovulation and regulating population size under unfavorable conditions (Konner and Worthman 1980) or a "terminal investment" in infants born later during the maternal life cycle (Williams 1966;Fessler et al 2005;Hoffman et al 2010). For example, the terminal children of Dobe !Kung mothers are typically weaned at 48 months, or as late as 60 months, although the average age of infant weaning is 28-35 months (Howell 2010).…”

Age-related patterns of reproductive success among female mountain gorillas

“…2a). This \age-order distinction" resembles many univariate analyses for birth weights of humans and chimpanzees, which also showed significant correlations with birth order but not maternal age (Fessler et al, 2005), but see (Roof et al, 2005). In our results, the age-order distinction arose because mothers had long a SBI when they reached a given birth order at a relatively young age (Table 3a).…”

Maternal Age and Offspring Adult Health: Evidence From the Health and Retirement Study

“…Birth weight may increase with maternal age (Fessler et al 2005), and low birth weight predicts adult diseases, such as coronary artery disease and diabetes (Barker 2002). The detrimental effect of higher germ cell damage of older parents may be offset by the increased longevity of those able to bear children later in life.…”