Monkeys can count...but not on an empty stomach

Even though they're one of our more distantly related primate cousins, macaque monkeys keep revealing remarkably human-like abilities. First they displayed self-awareness, and now it turns out they can count...but only if they don't get to eat what they're counting.

Researchers at the German Primate Center tested a bunch of macaques by offering them two plates with raisins on them. When the macaque pointed at one of the two plates, they were given their selection and allowed to eat all the raisins on it. In this test, the macaques didn't do well, often choosing the smaller of the two quantities.

But then the researchers switched the raisins for something the macaques couldn't eat, and the monkeys suddenly had no problem telling the difference between a lot and a little. Lead researcher Vanessa Schmitt explains that the macaques struggled in the earlier test because their hunger distracted them:

"This impulsiveness impaired their judgement. But when we repeated the test, this time showing them two plates of inedible objects - pebbles - they did much better.We wanted to know if they could simultaneously maintain two mental representations of the food items, first as choice, and second as food reward."

Then, just to thoroughly confuse the macaques, the researchers tried a third experiment, where the macaques again had to pick plates of raisins, but the food they got came from other raisins hidden underneath the plates. This meant the macaques could disassociate the visible raisins as food and just focus on picking the larger quantity, as Schmitt explains:

"They perform as well in this task as they do when choosing the pebbles. This seems to show that they see the raisins as signifiers - representations of the food rewards they're going to receive."

This is another experiment that puts macaques on roughly the same intellectual level as very small children. In fact, the results here are a close mirror for similar experiments done on young children, as Professor Julia Fischer explains:

"There's a well-known experiment called the reverse reward paradigm. You have two heaps of candies - one big, and one small. The child obviously points at the big heap - which is then given to another child, while the [first] child itself gets the small heap. Young children have trouble comprehending that they should point at the small heap to get the big one, but if you replace the candies with numerals or other symbols, they can do it."

Previous numeracy tests on primates that involved food may have been led astray by this effect, causing researchers to assume the macaques and other primates were less intelligent than they actually are.

Via BBC News.