In Stumbling On Happiness, Daniel Gilbert says that all psychologists are required, at some point in their careers, to write a sentence that begins with "The human being is the only animal that..." According to Gilbert, the answer is "imagines the future." My personal choice would be "wears socks with sandals," but I haven't done the field research to back that up.
A recent Discover Magazine article take a crack at this and comes up with the following answer: Humans are the only animals who teach.
At first, this seems like an overreach. Anyone who has watched chimpanzees interact has seen acts of imitation. It seems clear that other primates teach, and, just like humans, often do it for peanuts.
Discover Magazine is ready for this objection:
I know this may come as a surprise, but it does so because we tend to mix up teaching and learning. A young chimpanzee can learn how to smash nuts on a rock by watching an older chimpanzee in action. And when she grows up, her own children can learn by watching her. But in these situations, the students are on their own. They have to watch an action and try to tease apart the underlying rules.
I think we're about to head down a rabbit hole having to do with "intention" and the depth of conscious awareness in primates. Ultimately, this would be a pointless debate. The question is, "Is our children learning?" No, sorry, old joke.
The question is, "Has Learning Occurred?" We aren't necessarily going to know how it happened, who was responsible for it, or what the exact ingredients of the educational cocktail were. Therefore, it doesn't matter whether a child learns to tie his shoes because he was taught or because he imitated an adult. In fact, these distinctions are merely linguistic.
This discussion makes me think of the so-called "self-taught" learner. That term is a misnomer. The only self-taught learners we have on record are children raised by wolves or neglected in massive orphanages. Those children have little or no human contact. They must teach themselves. They don't do so well.
Just like you can't avoid learning (it's in our DNA), you can't avoid teachers. The world is a teacher. Maybe not on purpose, but it is.