Cats don't make lists, but they do enjoy sitting on them.

For hundreds of years people have attempted to define what it is exactly that separates us, the human beings, from the animals—or, more specifically, from our nearest relatives, the apes.

Some would say that we have souls and animals don’t. This argument has the advantage of not being scientifically disprovable, and the concomitant disadvantage of not being scientifically provable. And since I wish to speak with you today in the realm of science, we will leave that argument aside.

For a long time, people thought that what separated humans from the animals was the ability to use tools. Then someone noticed that chimps, for instance, use sticks to dig out termites to snack on. For a short while after it was proposed that what separates humans from the animals is that we don’t eat termites, but this turned out to be too narrow of a definition.

Later it was theorized that the ability to use language was the key distinction, but then Koko the gorilla started communicating in sign language, and that went out the door. Folks were starting to get a little desperate at this point, afraid that we were going turn out to be just apes with digital watches after all. It was proposed that only humans have culture, but primatologist Franz de Waal, for one, disagrees:

Culture, in de Waal’s estimation, does not mean using an oyster fork properly or attending smart gallery openings. Instead, it “means that knowledge and habits are acquired from others — often, but not always, the older generation.” Culture implies communication and social organization, and in this, he notes, humans by no means have a monopoly.

I am here today with what I believe to be a new slant on the topic. Man, I propose, is the only animal who makes lists.

This may seem trivial, but think about it: Any complex task requires a series of steps, which is a kind of list. You think they built the pyramids without lists? I really doubt it. Is the ability to classify, to organize, to order, not absolutely crucial to (what we consider to be) our success as a species? Looked at from this viewpoint, those of us who love to make lists are not borderline obsessive-compulsive, but quite highly evolved.

I suppose now someone is going to tell me that Koko makes a to-do list first thing every morning. Well, it’s really just the germ of a theory at this point; I would appreciate input from all you scientific thinkers out there.