Rhesus monkeys have joined the select group of primates able to count and to recognise numbers, according to research just published in the Journal of Experimental Psychology: Animal Behavior Process.
Three monkeys were trained by researchers from Columbia University in the US to organise computer displays offering collections of either one, two, three or four shapes, arranging the groups in either ascending or descending order.
To determine whether the monkeys understood the relationship between the numbers, for example that four is greater than three, the animals were tested again using groups of shapes numbering from five to nine.
The monkeys were quickly able to arrange these larger groups of shapes, ranking them in the correct ascending or descending order.