Monkeys keep track of small numbers

Without any training, rhesus monkeys recognize when the number of other monkeys’ voices that they hear corresponds to the number of monkeys’ faces that they see. This new finding indicates that monkeys accurately count small quantities that are relevant in their social worlds, say psychologist Kerry E. Jordan of Duke University in Durham, N.C., and her colleagues.

Evidence of counting by monkeys also supports the idea that basic number skills don’t require an understanding of language (SN: 2/19/05, p.