Lateral cradling preferences in humans (Homo sapiens): similarities within families

Women (Homo sapiens) tend to cradle infants on the left side of the body. We report the results of a survey of family photograph albums. We found that left-side cradling frequencies (LCFs) are higher in women than in men and that there are strong significant correlations between the LCFs of mothers and daughters, sisters, and maternal grandmothers and granddaughters. There may be a genetic influence on lateral cradling tendencies; women's left-side cradling preferences were found to be repeated with subsequent children. Heritability of women's LCF has an upper limit of 0.82, and the regression of daughters' mean LCF on mothers' LCF gives a heritability of 0.93 +/- 0.29. The data may be interpreted in two ways: There may be sex-limited genes (i.e., genes that express themselves only in women) for lateral cradling preferences, or women may learn cradling preferences from their mothers and other female relatives.