Ethnic differences in birth weight, a predictor of developmental outcomes and health, have remained largely unexplained. Using data collected by the US National Center of Health Statistics, we first cross-tabulate birth weight according to whether the mother or father was African American, European American, Native American, or Mexican American. Results confirm findings from other studies indicating the importance of maternal effects. Furthermore, traditional health and socioeconomic variables account for only a modest part of the group differences, and mothers who presumably lived in the most advantageous environments did not give birth to the heaviest babies. Next, we discuss the possible nature of the relevant maternal factors. Specific candidates include cultural differences in lifestyle that are traditionally not measured in large-scale surveys. Multiple lines of evidence in the literature also suggest that maternal genes are involved
