- Like all primates, lemurs are related to humans through a common ancestor that lived as many as 65 million years ago.

Scientists believe lemurs share many characteristics with those earliest primates, making them a window, though a blurry one, into our ancient past.

- Got a choice here, Teres.

Come on up.

- Duke professor Liz Brannon investigates how well lemurs, like Teres here, can compare quantities.

- We need to figure out whether they can really use number, pure number, as a cue.

- To test how well Teres can distinguish quantities, he's been taught a touchscreen computer game.

The red square starts a round.

If he touches it, two squares appear containing different numbers of objects.

He's been trained that if he chooses the box with the fewest number, he'll get a reward, a sugar pellet.

A wrong answer?

- We have to do a lot to ensure that they're really attending to number and not something else.

- To make sure the test animal is reacting to the number of objects and not some other cue, Liz varies the object, size, color, and shape.

She has conducted thousands of trials and shown that lemurs and rhesus monkeys can learn to pick the right answer.

- Teres obviously doesn't have language, and he doesn't have any symbols for number.

So is he counting?

Is he doing what a human child does when they recite the numbers one, two, three?

No.

And yet, what he seems to be attending to is the very abstract essence of what a number is.