56. McHenry 1992, 1996; Anton 2003.
57. Aiello and Wheeler 1995.
58. Hernandez-Aguilar et al. 2007; McGrew 2007b.
59. O’Connell et al. 1999; Wrangham et al. 1999; Laden and Wrangham 2005.
60. Perry, Dominy, et al. 2007. See Hernandez-Aguilar et al. 2007 for the lone exception of a savanna-dwelling chimpanzee population using shallow corms.
61. Yeakel et al. 2007.
62. See Alperson-Afil et al. 2007 for early use of fire. O’Connell et al. 1999; Wrangham et al. 1999.
63. Hawkes et al. 1998. For early insights into the importance of carrying and sharing, see Lancaster 1978.
64. Bock 2002.
65. Ivey 1993.
66. McDade et al. 2007.
67. Kaplan, Hill, et al. 2000.
68. Hrdy 1981a; Gowaty 1997; reviewed in Liesen 2007.
69. See published proceedings in Voland et al. 2005.
70. Whether or not other primates experience menopause remains a contentious topic (Pavelka and Fedigan 1991), but in his recent overview and evaluation of the literature, Paul (2005) concludes that they do; see also Hrdy 1981b. In the only Great Ape study of its kind, Jones et al. 2007 conclude that ovarian depletion with age occurs in chimpanzees at the same rate as it does in humans.
71. Leonetti et al. 2005:204.
72. Schiefenhövel and Grabolle 2005.
73. Voland and Beise 2002, 2005; Lahdenperä et al. 2004.
74. Lahdenperä et al. 2004; mortality rate calculated from Table 1. The effects were unlikely to be due to fertility differences between lineages since there was no relationship between post-reproductive longevity and the total number of offspring a woman herself bore during her life.
75. In addition to two anthologies edited by Voland et al. (2005) and Bentley and Mace (2009), see Aubel et al. 2004; Crognier et al. 2002; Gibson and Mace 2005; Jamison et al. 2002; Lahdenperä et al. 2004; Scelza and Bliege Bird 2008; Skinner 2004; Valeggia 2009.
76. Sear and Mace 2008. These societies were selected because the relevant information on both group composition and child survival was available rather than because they were a representative human sample across all ecological conditions. For the time being, it’s the best we can do.
77. Hawkes et al. 1998 and references therein; Lahdenperä et al. 2004 provide clear evidence that grandmothers have the biggest impact on their daughters’ early-born compared to later-born children.
78. Sear, Steele, et al. 2002; Beise 2005.
79. See Schiefenhövel and Grabolle 2005 for Trobrianders. For entry into what is now an enormous literature on the correlation between lack of social support, increased stress, and susceptibility to disease see Taylor 2002 and Flinn et al. 2005 for humans, and Sachser et al. 1998 and Kaiser et al. 2003 for social mammals generally.
80. Shostak 1976:256.
81. Flinn and Leone 2006; Quinlan and Flinn 2005.
82. See Lahdenperä et al. 2004 for an unusually well documented example of greater grandmaternal impact for early-birth-order children.
83. For example, Blurton Jones et al. 2005b.
84. Back in 1999, O’Connell et al. had predicted that “grandmothers could certainly have improved their fitness by aiding sons, but the benefits associated with helping daughters are likely to have been much greater” (p. 477). This is what Sear and Mace found in their 2008 overview using data sets from 28 traditional societies (Tables 2a and 2b). These findings were consistent with the pattern found in their detailed Gambia case study (discussed in Chapter 3) where presence of the mother’s mother was correlated with increased child survival, while presence of the father’s mother was correlated with increased fecundity. Sear et al. 2000, 2002; Mace and Sear 2005.
85. See Hrdy 1999, ch. 13, for review of a vast literature on parental preferences for particular offspring sets. See pp. 323–325 and Fig. 13.2 for the case of the ill-fated twin.
86. For why we would expect this, see Smith 1991 and Euler and Weitzel 1996 for early studies of differential solicitude from maternal and paternal grandparents. Similar patterns have since been replicated for a wide range of contemporary and traditional societies (Pashos 2000; Nosaka and Chasiotis 2005; Schölmerich et al. 2005, and references cited below). See esp. recent comparative analysis across 42 societies (Sear and Mace 2008).
87. Voland and Beise 2005; Beise and Voland 2002.
88. Euler and Weitzel 1996; Gaulin et al. 1997; McBurney et al. 2001; Voland and Beise 2005.
89. See Beise 2005 for Canadian case study; Sear and Mace 2008 for West Africa.
90. Jamison et al. 2002. Because of the small sample size, the maternal grandmother’s effect was not statistically significant, although with larger numbers the authors expect it probably would be.
91. This hypothesis predicts that such pernicious effects will be most pronounced where there are multiple sons.
92. See Borgerhoff Mulder 2007 for an exemplary case study among the Kipsigis of Kenya.
93. Leonetti et al. 2005:212.
94. Leonetti et al. 2005:209–210.
95. This increased survival was only statistically significant for mothers married for a second time. See Leonetti et al. 2007 for further explanation.
96. Sear 2008.
97. Regarding conflicting maternal and paternal interests see Strassmann 1993; Hrdy 1997, 1999:257–263.
98. On the custom of suttee, see Weinberger-Thomas 1999 and references therein.
99. Ivey 2000 for Efe; Blurton Jones, Hawkes, and O’Connell 2005b for Hadza. Sear and Mace (2008) found that paternal grandfathers had a positive effect on child survival in only 3 of 12 societies, maternal grandfathers in 2 of 12. Even when grandfathers had an effect, it tended to be of borderline statistical significance, or it only applied to granddaughters.
100. Judge and Hrdy 1992.
101. Polly Wiessner, personal communication, March 2008.
102. Wiessner 2002b, esp. pp. 424–425, Table 3, and references therein.
103. Harcourt and Stewart 2007, ch. 11. In the gorilla case, increased infant survival is mostly due to reduced probability of infanticide by outside males.
104. Marlowe (1999a) presents this patriarch hypothesis as an alternative to the grandmother hypothesis.
105. For whales see McAuliffe and Whitehead 2005 and references therein. Elephants are also said to experience menopause, but at least some females are still giving birth in their sixties.
106. Robson et al. 2006, Table 2.1. We do not know yet whether menopause in other apes is a universal trait. See Paul 2005.
107. The proposal by Cant and Johnstone (2008) is also based on the presumption that all apes, including humans, are patrilocal, a view at odds with much work summarized here.
108. Kurland and Sparks 2003; Hawkes and Blurton Jones 2005; Ivey 1993; Meehan 2005.
109. See Hurtado et al. 1992; Hawkes et al. 1995; Bird and Bliege Bird 2005; and Tucker and Young 2005 for empirical evidence from field studies.
110. See Hames and Draper 2004 for an overview of the effects of the transition from hunting and gathering to settled living, and Kramer 2005a for how children help in a farming society. The introduction of wage labor brings further transformation since sons typically earn more and contribute more than daughters to the household economy (e.g., Hagen and Barrett 2007).
111. See Kaplan 1994 for classic paper using data from traditional societies in Africa and elsewhere to demonstrate the direction of resource flow from old to young.
112. See for example the contemporary case of old men in modern Japan denied welfare benefits and permitted to starve to death (Onishi 2007).
113. For attitudes towards and treatment of old women see Biesele and Howell 1981; Hrdy 1999:282 and references therein. For quotation and more on Ache case, see Hill and Hurtado 1996:235–237.
114. Eder 1985. Quotation from Miller 1976, cited in Gilligan 1982:169; see also Taylor 2002 and extensive literature therein.
115. Campbell 2002.
116. T
aylor 2002.
117. Wiessner 2002b:411.
118. Hrdy 1999, ch. 10, 2000. Parish 1994.
9. CHILDHOOD AND THE DESCENT OF MAN
1. Hawkes et al. 1998.
2. On the high cost of motherhood and increased mortality risks for mothers in a nonhuman primate, see Altmann 1980:36. For humans, see Penn and Smith 2007. For general case of greater longevity in individuals who fail to breed, see Partridge et al. 2005. For decreased adult mortality in cooperatively breeding birds see Russell 2000. See Keller and Genoud 1997 for eusocial insects and naked mole rats. A honeybee queen can live up to 47 times longer than workers (Page and Peng 2001).
3. I am glossing over important current debates in evolutionary anthropology. For readers seeking a comprehensive overview I highly recommend The Evolution of Human Life History, edited by Hawkes and Paine (2006). The conventional anthropological explanation for long childhoods is that an extended period of maturation was essential for the development of big brains. “The adaptive function of prolonged biological youth,” it was assumed is “to give the animal time to learn” (Washburn and Hamburg 1965, cited in Hawkes 2006:97). Current versions of this embodied-capital hypothesis emphasize how many years it takes to acquire skills needed to track, hunt, and efficiently process big game; to expertly flake stone tools and craft spears; and to develop language and more fully take advantage of what culture has to offer (Kaplan et al. 2000; see also Kaplan et al. 2001; Bock and Sellen 2002; and Gurven and Kaplan 2007 for more on the importance of learning and benefits of growing slowly). The main alternative explanation for long childhoods relies on models that use “invariant” life history relationships to explain why mammals with larger body sizes have longer lifespans, mature at later ages, and produce babies at a slower pace (Charnov 1993; Robson et al. 2006). There is much to recommend these two hypotheses, which in any event are not mutually exclusive, and depend on complex feedback loops.
4. Hawkes et al. 1998; Robson et al. 2006. Regarding the correlation between large brain size and long juvenile and adolescent life phases see Smith and Tompkins 1995:259ff; Barrickman et al. 2008; Kelly 2004; Dunbar and Shultz 2007. Regarding the significance of larger brain size, see Deaner et al. 2007; Ricklefs 1984. See Janson and van Schaik 1993 on why immatures should grow slowly.
5. On the expensive-tissue hypothesis, see Aiello and Wheeler 1995. For background and overview, see Bogin 1997. On the relation between cooperative breeding and big brains see Isler and van Schaik 2008.
6. Hrdy 1999:287; Kelly 2004.
7. See esp. Robson et al. 2006; Deaner et al. 2007.
8. Walker and Shipman 1996; Anton 2003.
9. Tardieu 1998:173–174; Smith and Tompkins 1995, Table 1; O’Connell et al. 1999:469; Robson et al. 2006; Hawkes 2006, but see Zihlman et al. 2004.
10. Anton 2003; McHenry 1992, 1996.
11. O’Connell et al. 1999, 2002.
12. Presumably, the need of mothers to avoid nutritional depletion from pregnancy and lactation is why among tribal peoples in highland New Guinea, women and children have preferential access to all edible insects that men harvest (Schiefenhövel and Blum n.d.). See Stoll 2001:91–102 for the importance of omega-3s during pregnancy and fetal brain development. Hominins in the early Paleolithic probably did not often, if ever, have access to fish, but we know that wherever and whenever they are available, tree nuts—often an even denser source of omega-3 fatty acids than fish—are a staple food among African apes as well as hunter-gatherers (e.g., Boesch and Boesch-Achermann 2000:201–204; Lee 1979, ch. 7).
13. Although females are bonded to matrilineal kin in most Old World monkeys, lack of “tolerance” between unrelated females is thought to characterize apes in the line leading to Pongo, Gorilla, and Pan (e.g., Rendall and Di Fiore 2007, Fig. 2).
14. This was perhaps the most important lesson I learned while researching an earlier book, The Woman That Never Evolved (1981a), and references therein.
15. Quotations from Tomasello 1999:91. See also Tomasello et al. 2005.
16. Personal communication (2006) from Karlen Lyons-Ruth, who specifically acknowledges her debt to Tomasello (1999); quotation from Hennighausen and Lyons-Ruth 2005.
17. D’Errico et al. 2005; McBrearty and Brooks 2000. For quotation, and much more on origin of art, see Dissanayake 2000.
18. For an excellent discussion, see Hill 2009.
19. One could mention here Old World monkeys who attack an individual who fails to defer to immature offspring of a dominant lineage (Cheney and Seyfarth 2007) or who attack an individual and take away a preferred food item he had found because the finder failed to signal that he was prepared to defend it (as in Hauser 1992). But the closest nonhuman primates come to intention-reading derive from experiments like those done by Marc Hauser and others with cooperatively breeding tamarins and marmosets, described in Chapter 3. It is worth noting that Hauser himself, one of the pioneers in this area, is now reluctant to talk about group sanctioned “punishment” in nonhuman animals (personal communication, August 2008).
20. Hill 2009.
21. Fu and Lee 2007. I am indebted to Judith-Maria Burkart (2009) for this observation.
22. Wile et al. 1999; Miller 2002; Hagen and Barrett 2007.
23. See Trivers 1974, whose theories on parent-offspring conflict are now widely accepted in biology and psychology.
24. Hennighausen and Lyons-Ruth 2005:275.
25. Stern et al. 1983; Stern 2002; Cassidy and Shaver 1999; and esp. Rutter and O’Connor 1999 and Main 1999; O’Connor and Rutter 2000; Fonagy et al. 2002; Belsky 2005.
26. Lyons-Ruth et al. 1999; van IJzendoorn, Schuengel, and Bakermans-Kranenburg 1999.
27. To assess how secure a child feels about his relationship to a main caretaker, who in most of the research done to date means the mother, psychologists employ Ainsworth’s Strange Situation test. In this 20-minute protocol, the mother leaves her toddler together with a kindly “stranger” who is in fact a trained experimenter. The mother then returns, goes away again, and comes back. Most two-year-olds become distressed as soon as they note her absence, but the “securely attached” child will rush to her as soon as she returns and soon be comforted. However, some children fail to find her return reassuring. These “insecurely attached” toddlers can be further subdivided into those who seem “insecure/ambivalent” about just how much comfort they can derive from being near their mother and those who actually “avoid” their mothers, the “insecure/avoidant.” For more on this topic, start with Cassidy and Shaver 1999.
28. Main and Hesse 1990; Lyons-Ruth et al. 1999; van IJzendoorn, Schuengel, and Bakermans-Kranenburg 1999; Solomon and George 1999.
29. Lyons-Ruth 1996. See Rutter and O’Connor 1999 for related disorders.
30. Dozier, Stovall, et al. 2001; see also Bates and Dozier 2002. On Adult Attachment Interviews, see Main and Hesse 1990. For a meta-analysis showing the predictive validity of AAI based on 80 studies encompassing some 6,000 children see van IJzendoorn, Schuengel, and Bakermans-Kranenburg 1999.
31. On heritability of personality traits like shyness or sociability, see Kagan and Snidman 2004. On lack of a relationship between attachment styles and the “Big Five” personality traits, see Shaver and Brennan 1992. For temperamental variation in monkey infants see Thierry 2007 and references therein.
32. Hennighausen and Lyons-Ruth 2005:385–386; Lyons-Ruth and Zeanah 1993; Rutter and O’Connor 1999.
33. Berlin and Cassidy 1999. See Vaughn, Azria, et al. 2000 on correlation with friendship and “social competence.”
34. Lyons-Ruth 1996, and personal communication in 2008 interview.
35. Hawks, Wang, et al. 2007; see also Harpending and Cochran 2002; Balter 2005. Lactase persistence is perhaps the best-known example of recent selection. Milk, the staff of life for infants, can be difficult stuff for adults to digest unless they produce lactase, the enzyme that breaks down its main sugar, lactose. At some point between 5,000 and 10,000 years ago, as some cultures adopted
herding, a gene conferring lactase persistence past infancy began to spread along with cattle-herding immigrants from the Near East to areas of Europe that increasingly relied on milk products. Today, the gene for lactase persistence is found in 80 percent of Europeans and of Americans whose ancestors evolved in Europe. It is also common among Tutsi and other African tribes with histories of herding. However, it is almost entirely absent from groups whose ancestors did not milk cows, including South African Bantus and many populations in China (Bersaglieri et al. 2004; Burger et al. 2007).
36. J. Hawks, personal communication, December 31, 2007. Regarding rapid spread of new gene variants for increased brain size, see Mekel-Bobrov, Gilbert, et al. 2005.
37. Spier 2002.
38. For general theory see West-Eberhard 2003. On the evolutionary loss of prosocial behaviors, see Wcislo and Danforth 1997. For a case study in rapid evolution, see Lahti 2005. Lahti describes how warbler parents transplanted to locations lacking brood parasitical cuckoos gradually lost the ability to distinguish their own eggs.
39. Lahti 2005.
REFERENCES
Adovasio, J. M., Olga Soffer, and Jake Page. 2007. The invisible sex: Uncovering the true role of women in prehistory. Washington, DC: Smithsonian Books.
Ahnert, Lieselotte. 2005. Parenting and alloparenting: The impact on attachment in humans. In Attachment and bonding A new synthesis, ed. C. S. Carter et al., 229–244. Dahlem Workshop Reports. Cambridge: MIT Press.
———. 2007. Mother-child relations with extended social networks in early childhood. Lecture delivered at the University of California-Davis, March 15, 2007.
Ahnert, Lieselotte, Martin Pinquart, and Michael Lamb. 2006. Security of children’s relationships with nonparental care providers: A meta-analysis. Child Development 74:664–679.
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