To test whether the monkeys understood the ordinal relations between non-consecutive numbers -- that, for example, five is greater than three -- Ms. Brannon and Prof. Terrace gave the monkeys a new set of problems in which they were shown up to nine objects. The task was to first touch the picture containing the smaller number of objects, then the one with the larger number of objects. For example, if a monkey was shown one picture with five large circles and another containing seven small circles, the correct order was five, then seven. Rosencrantz and Macduff responded correctly even when the number of objects in the pictures exceeded four.
"This finding is important because it shows that monkeys know things about number that we haven't taught them," Ms. Brannon said.
Ms. Brannon and Prof. Terrace believe that arithmetic and language evolved separately, and that number skills preceded human speech. "Language is a complex social skill, whereas counting can be learned by the individual," Prof. Terrace said. "Counting is useful in foraging for food, assessing a group of predators or ordering the number of dominant males in one's group."
With further studies, the research team hopes to answer other questions
on language and numerical abilities in non-human primates. Do monkeys, like
humans, immediately identify small numbers of objects without counting? Could a
non-human primate learn to match two different pictures of three objects, one
containing, for example, three circles, the other, three triangles? Can monkeys
learn symbols that represent numbers? How hard would it be for a monkey to
learn a nonconsecutive numerical sequence, for example, three-one-four-two? Ms.
Brannon and Prof. Terrace believe that these, and similar experiments on the
numerical ability of animals, will provide a unique window into the evolution of
Contact: Bob Nelson, Office of Public Affairs