Paternal Instincts

The evolution of fatherood shows shocking similarities in humans and animals and appears nothing like a mother’s connection to her baby.

Major changes occur in the metabolism of males during the pregnancy of the partner. They increase the fat deposits, as a response to higher levels of circulating prolactin, the same hormone that in females stimulates milk production. Male prolactin exists naturally in low level but tends to increase when the female is pregnant. It is the result of psychological empathy that connects mind and body through hormonal changes and can be traced thoughout all mammals.

In the early days after birth, more changes occur in the brains of both the father and the newborn. In response to a baby’s cry, certain areas of the father’s brain become activated with a signature pattern quite different from that of non-parents who are hearing the same sounds.

Fatherly feelings are parallel but not identical to the baby and mother bond. A father’s brain produces new neurons in many areas, a process called neurogenesis, which is connected with learning new things. The neuronal cells form brand-new connection pathways, or circuits as well, in the days following the birth of the babies. Another set of neurons grow in the father’s hippocampus, a center for the memory in the brain, which probably helps to consolidate the features of their babies into long-term memory and forms a lasting bond.

However, mammal fathers only gain the extra brain cells and new connections if they remain hands on in physical contact with the offsprings and experience their smells.

Scientists still struggle to understand why new neurons originate in the brain of all mammals, including humans. Human fathers producing higher levels of oxytocin also called the ‘love hormone’ show stronger paternal instincts and motivation in the first months of their child’s life.

Marmoset father monkeys constantly feed their youngsters during the first six months, but after that period the fathers start to ignore their adolescents, and keep the food for themselves. What causes this change is actually a decreased level of oxytocin.

Where prolactin and oxytocin are both heavily associated with fatherhood interactions, the hormone that modulates stress response, corticosterone, has been blamed of creating structural changes in the mammalian father’s brain.

Positive stressors such as exercise boost corticosterone levels. Therefore, we can easily conclude that fatherood is no less that an exercise in this matter.

Printed in Petigree Magazine Oct / Nov 2013 issue