Evidence of environmental suppression of familial resemblance: height among US Civil War brothers.

This study examines, with historical data, whether within family correlations in height varied across environments and whether variability in height was greater in worse environments. To investigate these hypotheses, brothers were identified who were mustered into the Union Army of the US Civil War, using linked records from the 1850 and 1860 censuses and military and medical records. Heights were available for 3898 men aged 18 and older, of whom 595 were further identified as belonging to 288 family sets of two, three or four brothers. Generalized estimating equations were used to concurrently model the mean height, the variance and the correlation between brothers as a function of county population. Heights decreased as county population size increased (p<0.001). The correlation between brothers' heights decreased significantly (p = 0.032) with increasing county population, and the variance increased (p = 0.026). The correlation ranged approximately from 0.63 in the least populous to 0.24 in the most populous counties. The degree of familial resemblance was lower in environments where mean height was lower, and the variability in height was greater, suggesting that the environmental contribution to the variability in height is of greater relative importance in populations reared, on average, in worse environments.