Thanks largely to the Hadza (Photograph 18.1), grandmothers have drawn attention from many researchers in recent years (Hawkes et al., 1989, 1997, 1998, 2011; Hawkes, 2003; Lahdenpera et al., 2004; Voland et al., 2005; Sear and Mace, 2008). The attention given to grandmothers illustrates an important scientific tradition: give maximal attention to things that appear not to fit the dominant theory. Grandmothers are a major evolutionary conundrum. Natural selection is generally weaker on the old than the young, and cannot act on characteristics of individuals who no longer reproduce. Hence, why do hunter-gatherer women live on average 23 years after their final birth (Blurton Jones et al., 2002)? Many, since Hamilton (1966), have suggested that our species breaks the rule by virtue of the help that older women can give to their children and grandchildren, thus influencing their own inclusive fitness long after they have ceased childbearing. Some have argued against this idea, by suggesting that grandmothers would be few and ineffective in earlier times.

In this chapter, I address the availability and effectiveness of Hadza grandmothers’ help. First, I show how many women and children have an older helper, and how many older women have small children they could help. Then I give special attention to whether grandmothers affect children's growth and survival, examine some alternative explanations for the results, and look at some of the details. I go on to look at whether grandmothers affect their daughters’ fertility, inter-birth intervals (IBIs), and reproductive success. In the next chapter, I discuss models, theory, and debates in the field. While Hawkes (2003), Hawkes and Smith (2010), and Jones et al. (2007) have set the primary problem as accounting for evolution of post-reproductive life, others take lifespan as a given, and aim to account for shortened reproductive careers. Some have examined a trade-off between continued reproduction, and care for descendants (Hill and Hurtado, 1991), and others have looked at competition between the generations (Cant and Johnstone, 2008; Johnstone and Cant, 2010).

Hawkes et al. (1989, 1997, p. 552) and Kaplan (1997, fig. 10–4) suggested that in habitats in which weaned offspring could not feed themselves, and where food came in large packages that were difficult to acquire, selection would favor kin who provided food for the offspring (Hawkes et al., 1989).