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14 Cooperation and Competition in a Cliff-Dwelling People--BEVERLY I. STRASSMANN
Pages 303-324

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From page 303...
... growth and survival in the Dogon of Mali, I show that cooperative breeding theory is a poor fit to the family dynamics of this population. Rather than helping each other, siblings competed for resources, producing a tradeoff between the number of maternal siblings and growth and survival.
From page 304...
... concluded that coopera tive breeding was prevalent in traditional farming populations that had high fertility and high mortality, but only 6 of 17 studies controlled for wealth. A meta-analysis showed that the positive association between grandparental and grandchild survival was found only for the maternal and not the paternal side, although in these farming populations, the children were more likely to live with their paternal grandparents (Strassmann and Garrard, 2011)
From page 305...
... The Dogon retain many of the features that have characterized humans over our evolutionary past, including the absence of contraception, polygyny, preservation of the indigenous religion, a subsistence economy, life in a tight-knit web of close and more distant kin, and high mortality levels (Strassmann, 1992, 2000)
From page 306...
... The other variables controlled include child's age, year of study, sex, age by sex interaction, village of residence, survival of the paternal grandpar ents, sex by survival of the father's mother interaction, sex by survival of the mother 's mother interaction, birth order (mother 's offspring) , standardized wealth rank, and mother's marital rank ( n = 572 and the ages of the children were 41–98 months)
From page 307...
... . Children's work is also cooperative; however, it is not directly analogous to coopera tive breeding in birds and other mammals because the latter refers to the postponement of personal reproduction caused by constraints on independent breeding opportunities (Emlen, 1997a)
From page 308...
... Solid lines females; dashed lines males.
From page 309...
... If extended families are preferable, then children should survive better when there are more married adults in the WEG. Kin selection theory does not make a prediction about WEG size per se, but it does predict increased conflict in WEGs that have more asymmetries in genetic relatedness, such as in polygy nous WEGs.
From page 310...
... who emerged as overwhelmingly important for child survival was the child's own mother (Table 14.2)
From page 311...
... , I compared the growth of Dogon children to the World Health Organization's healthy international reference population (World Health Organization, 2005)
From page 312...
... Instead, there was no significant difference in child survival when the WEG boss was the child's father, paternal grandfather, maternal grandfather, or father's brother (Fig. 14.5 and Table 14.2)
From page 313...
... . The finding that runs counter to kin selection theory is the lack of difference in survival between children whose father was the WEG boss vs.
From page 314...
... occurs along kinship lines. I tested this hypothesis using data on WEG stability from pedigree data for 29 Dogon patrilineages in nine villages.
From page 315...
... Kin selection theory predicts important aspects of WEG dynamics such as the conflict among cowives and sisters-in-law and the circumstances that trigger WEG fis sioning. The person in the WEG who is most important for child survival is the child's own mother, a finding also seen in other demographic datasets (Sear and Mace, 2008)
From page 316...
... In each year of the study, the family structure variables were used to predict the change in a child's height-for-age z score from one year to the next (Methods)
From page 317...
... mother 's mother, and mother 's father was unrelated to grandchild growth rates (Fig.
From page 318...
... A possible evolutionary explanation is local resource competition (Clark, 1978)
From page 319...
... , standardized wealth rank, mother's marital status (fiancée, polygyny, or monogamy) , and nursing by mother's marital status interaction.
From page 320...
... CONCLUSION ww.pnas.org/cgi/content/short/1100306108 If the term cooperative breeding is restricted to human popula tions in which adult offspring delay or forego reproduction to act as helpers, then the Dogon would not qualify because girls usually initiate reproduction by about age 19 years and boys by age 25 years. It would potentially apply, however, to 19th and early 20th century European f arming communities in Ireland and elsewhere that had an unusually high percentage of individuals who postponed reproduction to their thirties or who were permanently celibate.
From page 321...
... These results do not align with the expectations of cooperative breeding theory. Kin selection theory was more helpful for understanding the dialectic between cooperative and competitive interactions in the Dogon, especially when conjoined with parent–offspring conflict and life history theory.
From page 322...
... Therefore, in studying the relationship between family struc ture and child survival, I used the field data from the years 1998–2001. The statistical analysis employs a Cox proportional hazards model to analyze survival as a function of time-varying covariates (Cox, 1972; Allison, 1995)
From page 323...
... The statistical models included a random effect for mother. Behavioral Data From 1986 to 1988, an instantaneous behavioral scan was conducted during daylight hours in the fields and the initial study village in all months of the year.
From page 324...
... I thank Kathy Welch for statistical advice and Claudius Vincenz, Laura Betzig, and two anonymous reviewers for helpful comments. This research was supported by the Louis S


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