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Differential Parental Investment in the Southwestern United States

ABSTRACT 
 The Trivers-Willard model (1973) predicts differential parental investment in children by sex and income; wealthier families will invest more in boys, while poorer families will invest more in girls. We investigated the TW Hypothesis in a sample of 103 six month old Tucson babies and their mothers. Hierarchical multiple regression equations were used entering baby's age, baby's sex, mother's age, male paternal commitment, a dichotomous poverty measure, per capita income, and four interaction terms, baby's sex by 1 ) mother's age 2) mother's education, 3) male paternal commitment, 4) poverty, and 5) per capita income. We included three dependent variables in successive regression equations; mother's attitudes towards ideal baby size for boy versus girl babies, weeks breast fed and the baby's weight at six months. These variables measure attitude, behavior, and physical outcomes. Poverty was a significant predictor of differential preference in ideal body size for boys versus girls; poor mothers preferred bigger baby girls. There was no evidence of differential preference in breast feeding. Education was also a significant predictor; but in the opposite direction than predicted by the TWH. Mothers with higher levels of education had heavier baby girls. Within Hispanics only, poverty was a significant predictor of sex-biased weight; poor mothers had heavier baby girls. This effect was not seen in Caucasians. These results provide mixed evidence for the Trivers-Willard model in a resource rich environment for humans.