Laughter and the soul: Proof from the rat tickling experiment

by John MacBeath Watkins

Aristotle thought the soul entered a baby when it first laughed, which he estimated happened about 40 days after birth (recent research indicates it's more like 90 days for most kids, but Aristotle may have been truly hilarious by baby standards.).

And that's important, because the age of ensoulment is generally considered the age at which the baby
Was Aristotle available
for children's parties?
is human. St. Augustine thought ensoulment happened at the quickening, that is, when the mother could feel a baby kick. As long as this was Catholic doctrine, abortion was permitted until the quickening.

But what interests me here is the question of why Aristotle would choose, among all baby vocalizations, laughter.

What does laughter mean? It doesn't always occur when someone has made a joke. In fact, it seems to mean, "we're just playing." And play, as Karl Groos noted in his 1898 book, The Play of Animals, is important because it is how young mammals of all species learn. In fact, he said that it is not so much that animals play because they are young, it is more like they have a period when they are most inclined to play so that they may learn.

Aristotle was the sort of polymath who had theories about everything. He even wrote a natural history book, the title of which is usually translated History of Animals, in which he attempted to sum up what was known about zoology. He also wrote a book on comedy, of which unfortunately there are no extant copies.

It was in The Parts of Animals (De Partibus Animalium), a book on anatomy, that he speculated warm air most easily reaches the soul through laughter. Barry Sanders, author of Sudden Glory: Laughter as Subversive History, says that Aristotle thought only humans laughed, and only laughter could animate the soul, which is why he thought laughter separated humans from animals, and called us animal ridens, the beast who laughs.

However, scientists have determined by tickling rats that they laugh. In fact, it seems to be a behavior common to all the mammals they have managed to tickle.



In short, animal ridens is not a mere genus, it is an entire class of animals, the class of animals who play. Aristotle, however, thought laughter was connected to a sense of superiority, which makes me wonder about his sense of humor. He said people laugh at an ugly mask during a play because they can feel superior without causing pain. Perhaps he was fond of slapstick, of seeing people do silly things.

But I do think he was on to something with his theory about the importance of laughter. Perhaps laughter signals that the baby is ready to move beyond instinct, to engage in the sort of play that will enable it to learn behaviors that are invented rather than instinctive. The longer childhood lasts, the longer an animal is supposed to engage in play, which may tell us how much of a species' behavior is passed on through teaching rather than through genes, although there are probably adjustments for size (nerve impulses move the length of a shrew more quickly than they move the length of a whale, so they may be living and learning quicker.)

So what was Aristotle seeing that made him think a baby was ensouled when it first laughed? Well, in its first days, a baby is a creature of inarticulate appetites. It cries because its wet diaper is uncomfortable, because its belly is empty, because it is too cold or too hot. It learns to smile in the first month, but the first vocalization that says, "I am playing, therefore I am learning," is laughter.

Aristotle was a teacher, which may be why he noted the insolent laughter of youth. Unlike his fellow teacher, the more dour Plato, he approved of laughter in moderation. Perhaps he noticed that people who laughed together liked each other more. Perhaps he even noticed that students who were laughing were learning.

But he did not notice that rats laugh when you tickle them, and therefore, by his standards, have souls.







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