If you have a pet, you’ve probably noticed it show affection at some point in time, and have, in reciprocation, shown your affection back too. But what are the evolutionary advantages of making physical contact with a conspecific, or another species?
Well, the induction of neurotransmitters across synapses could be one of the more basic and general answers. Hormones like oxytocin, dopamine, adrenaline and so on, are commonly stimulated by physical touch. But I’m more interested in more, specific advantages.
For example, sea otters (Enhydra lutris) hold each other’s paws when sleeping. The function behind this adorable behavior, is to prevent the two from drifting apart in their sleep.
Another, more well-known example is physical contact and communication in primates. Many monkeys and apes use physical contact to show their affection, but it is also used when grooming and communicating.
Another example, occurs in mice. When mother rats groom their offspring, they indirectly induce methylation of estrogen genes, effectively altering the stress levels and behavior of their daughters. In contrast, offspring that do not get groomed by their parents, appear to have their genes for stress hormones blocked, and become more susceptible to stress stimuli. For more information on how maternal grooming alters gene expression and responses in offspring, here is the article: