The skin sensors of the unborn begin functioning and send impulses of warmth and pressure to a developing brain that becomes capable of remembering those sensations before birth. In the current era, those are not politically correct beliefs but, nonetheless, research has indicated that they are factual.
When the newborn cry out against a relatively cold and lonely world, adults hold them close, thereby approximating sensations remembered from the womb. Content, infants drift off to sleep but wake again to cry out and quickly learn how dependably that behavior regains for them the distracting pressure and warmth that have been lost to birth.
This often reinforced stimulus-response pattern becomes a major learned behavior observable throughout a person's life. Toddlers can be seen trying to crawl up on an adult's lap and the elderly hug each other so the cuddling habit, formed before birth, exerts a powerful influence over human behavior from the cradle to the grave.