Two-ness

In a maths test based at a science museum, female volunteers recognised one to four dots more quickly than males did. Both sexes did equally well at counting larger numbers of dots.

The findings add to evidence that the brain deals differently with small and large numbers. We seem to have a built-in idea of 'two-ness' or 'three-ness', but must count to distinguish 12 and 13, say...

Why the brain treats small and large numbers differently is not clear. Some social animals - rats, lions and chimpanzees - can count, a skill that perhaps enables them to decide how their group should react to single or multiple intruders.

From Nature