No mammal may ever be as mathematically capable as humans are, but a new study suggests rhesus monkeys can at least use symbols to add.

According to LiveScience, the study researchers chose rhesus monkeys because they are more distant relatives of humans than chimpanzees. Rhesus monkeys and humans diverged about 25 million years ago, whereas chimpanzees did so about six million years ago.

Like many animals, both primates can estimate the number of items in a group and determine if one has more than the other. However, the researchers wanted to see if the monkeys had any more difficulty with comparing larger quantities.

"You would have trouble distinguishing 'oo o ooo ooo ooo ooo oo ooo' [a string of 20 symbols] from 'o ooo oooo oo oooo ooo ooo o' [a string of 21 symbols], but if I asked you whether 20 was larger or smaller than 21, you could answer faster and more accurately," study lead study author Margaret Livingstone, a neuroscientist at Harvard University Medical School, told LiveScience.

The team published their work in the journal Proceedings of the National Academy of Sciences.

The scientists created a reward system and associated 26 individual figures with anywhere from 0 to 25 drops of water, juice or orange soda. The monkeys would analyze one of the 10 numerals and 16 letters against another and chose the option with a larger reward 90 percent of the time.

"They turned out to be like us - more accurate when values were represented by symbols than by the number of dots," Livingstone said. "It tells us what good symbols are."

Even when the scientists changed the set if symbols the monkeys were looking at, they still exhibited the mental capacity to add and compare values.

"The monkeys did not memorize the addition of pairs of numerals; they just fairly accurately combined two symbols," Livingstone said.

David Burr, a psychologist at the University of Florence in Italy, was not involved in the study, but he told Science Magazine the ability to estimate and add is inherent, as it is necessary for survival.

"Being able to estimate obviously has survival value; you want to be able to glance up and see how many lions are about to attack you," Burr said. "The remaining goal is developing a model to explain how that happens in the brain."