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out using Proc Phreg in the statistical software SAS 9.2 (SAS Institute, Inc., 2008), which allowed for control for multiple observations of the same child. 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. The date, time, identification, and activity of each person were recorded (n = 5,097 observations).

Children’s Growth

I calculated height-for-age z scores in relation to the international World Health Organization (WHO) standard that is appropriate for breastfed children in developing countries (World Health Organization, 2005). These z scores quantify the distance (measured in SDs) of a given child’s height relative to the mean for the reference population. I calculated growth as the change in height-for-age z scores. The covariates in a given year were used to predict the change in the child’s height-for-age z score from that year to the next. The statistical analysis used a linear mixed model (Littell et al., 1996) that (i) used a repeated measures design to take into account the autocorrelation in the growth of a given child between years and (ii) included the mother of the child as a random effect to take into account the correlation among maternal siblings. The analysis was carried out using Proc Mixed in the statistical software SAS 9.2 (SAS Institute, Inc., 2008).

WEG Fissioning

Males (n = 1,218) belonging to 29 patrilineages in 10 villages provided genealogical information for their paternal and maternal ancestry as far back as they could remember. From the oral histories, I made patrilineal pedigrees in the program Progeny (Progeny Software, LLC, 2007) that have a depth of up to 11 generations from the youngest generation to the common ancestor. These pedigrees contain data on WEG composition and changes over time.


I thank the Dogon for their generous participation in this research, including my Dogon field assistants for their valuable help. I am grateful to the Malian government for permission to conduct this study and

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