Why we usually weigh babies in our left arm but carry toddlers on our right. The pattern is evident across cultures and centuries.
Even the Virgin Mary holds the baby Jesus in the crook of her left arm in many depictions. There are various theories about the reasons: One is that a baby is mainly carried on the left arm because it can then hear the heartbeat better. Another theory is related to sensory perception: the left ear and eye would be used to receive information about the baby's emotional state.