Humans and other animals are known to hold their offspring on the left-handside of their bodies in a practice called "left-cradling bias."
Scientists have long been puzzled over this behavior, but a recently published study by an international team of researchers largely attributes it to eye contact and brain processing.
According to the BBC, researchers found that the positioning encourages contact between the left eyes of the mother and offspring.
They believe that this, in turn, triggers the right side of the mother's brain which is considered to be responsible for visual processing.
See more related to this story:
As such, the mother could perhaps better identify her baby's needs by reading his or her expressions or help track her offspring if they were to get separated.
The paper explains that this exchange "reflects socio-emotional processes and potentially facilitates mother–infant relationships."
For the research, the team observed this interaction among humans and 10 other animals including whales, kangaroos, and reindeer.
The researchers were able to confirm that all of them showed this bias.