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In 1967 Dr. Bacon Chow and others initiated a longitudinal study in a marginally nourished population (Sui Lin, Taiwan) of the effects of maternal supplementation on subsequent growth and health of the offspring. Each mother provided two participant infants: during gestation of the first infant the mother was untreated, while during the lactation of the first infant and the gestation and lactation of a second infant she was treated with either a calorie supplement or a placebo. The pair of siblings offers a chance to assess the role of heredity as a mediator of supplement effects on physical growth and environmental covariation in physical resemblance of siblings. There were 108 pairs of siblings whose mothers had received a high calorie-protein supplement as described above and 105 pairs of siblings whose mothers had received a placebo. Among the latter, sibling correla­tions for most birth measurements are statistically significant, and of the same magnitude seen in previous studies (~ 0.5), while among supplemented siblings, correlations are unusually low and often insignificant. The sibling correlations for the following measurements differed the most between groups: birthweight and head circumference of male infants and Rohrer’s Index (wt/13) for infants of both sexes (p < 0.01). Group differences in the sibling correlation tended to disappear over the first year of life. These results suggest that: 1) maternal supplementation may affect components of variation of infant anthropometry more than means, 2) infant body proportions (Rohrer Index) may be more affected than size per se, 3) supplement effects on size may be sex dependent, males being more affected than females, and 4) there are important environmental contributions to the physical resemblance of siblings at birth.