of work (Blurton Jones et al., in press: figure 2). Reproductive-aged and postreproductive women acquire 1500 and 1670 Kcal/hr, respectively. A similar pattern is found among Hiwi hunter-gatherers, for whom roots are also the most important plant food.
Among some !Kung groups, mongongo nuts are reported to be the plant food staple (Lee, 1979). While the nuts are easy to collect, several factors appear to limit the productivity of children (see Blurton Jones et al., 1989, 1994a,b for an in-depth analysis). First, mongongo nut groves are often found quite distant from water sources (about 10 km) where camps are located (Blurton Jones et al., 1994a,b). This requires a great deal of endurance and the ability to walk far without much water (ibid.). In addition, extraction of nut meat requires skill. According to experimental data on nut-cracking rates (Blurton Jones et al., 1994a), most children under the age of 9 are unable to crack the nuts safely. Children aged 9-13 cracked 120 nuts per hour, teens aged 14-17 cracked 241 nuts per hour. and adults cracked 314 nuts per hour. Bock, who worked with villagers in the Okavango delta who practiced a mixed economy of hunting, fishing, gathering, horticulture, and animal husbandry, found that mongongo cracking rates peak at age 35 for women (Bock, 1995).
The most important plant food among the Aché is palm starch. Extraction of palm starch requires felling the tree, cutting a vertical window down the length of the trunk to expose the pulp, and then pounding the pulp into mush. This is a difficult task involving both strength and skill, and women do not reach peak productivity at palm-fiber extraction until age 35 (A.M. Hurtado. unpublished data). Again, Aché girls less than 15 years of age rarely pound palm fiber.
Seeds, an important plant food staple in Australia and the North American