Handedness and sex effects on lateral biases in human cradling: Three meta-analyses.

The earliest form of social contact for a newborn is being cradled by its mother. This important behavior has been found to be lateralized to the left side by many, but not all empirical studies. Factors that have been suggested to modulate cradling asymmetry are handedness and sex. However, these factors have not been demonstrated consistently, possibly due to low sample sizes and inconsistent experimental paradigms. To address this issue, we used a meta-analytical approach to (1) quantify the widely reported leftward bias in human cradling and (2) identify moderating factors of the cradling bias such as handedness and sex. Across forty studies, we observed a leftward cradling bias showing that this effect is robust and replicable. Furthermore, we found that left-handers demonstrate a significantly less pronounced leftward bias compared to right-handers and that males are less lateralized compared to females. In conclusion, we could verify that parental handedness and sex contribute to a cradling population bias. Future studies examining genetic factors could illuminate the mechanism supporting a cradling bias.