In the 15th Century, as is still the case today, unmarried young ladies would occasionally find themselves pregnant under socially-embarrassing circumstances. In Hampshire, England, it became common practice to take the newborns out to the Convent of St. Dympna, far out in the oak forest.
After dark, the nuns locked the front gates until sunrise. Children brought after hours were typically left on the front step.
Sometimes the children were old enough to crawl around a bit, though, and if sufficient care wasn’t taken to restrain them they might wander off from the front of the convent and into the woods.
The oak forests of Hampshire were famed for their population of pigs, which throve on the abundance of acorns. With such an abundance of food for most of the year, the pigs were generally very peaceful and easy-going. There are even a number of recorded cases where a mother sow adopted and cared for one of the abandoned babies who had wandered from the convent.
Some of these children grew up and rejoined human society. Having been raised in the wild by pigs, however, they usually didn’t get along well with other people. They tended to babble incomprehensibly, and to be totally ignorant of all etiquette and social rules. Most of them also retained their pig-related habit of rooting around under oaks looking for nuts. Thus, such people became known as “nutters”, and the term has lasted to this day and age to describe people with similar mannerisms.