Cones, which are responsible for colour vision, come in three varieties, each tuned to a particular wavelength.

ECONOMIST: The biology of art

Some areas identified as particularly human are the regulation of the cone cells of the retina (which are involved in colour vision) and the regulation of nerve-cell growth.

ECONOMIST: Evolution

"With my vision, when I look at the target, it looks as if different colour paints have been dropped in water, " he tells me.

BBC: Korea's blind' archer Im Dong-Hyun aims for 2012 gold