Chameleons were long thought to have developed the ability to change their skin coloration in order to blend in with their environment. But a study published last year in the journal PLoS Biology argues that chameleons evolved this ability to attract mates, scare away rivals, and send other social signals--not for camouflage (at least, not initially).

The presence of chromatophores, or pigment cells, in their skin allows chameleons to change color to pink, red, orange, green, black, and other hues. The color patterns can change in just a few thousandths of a second.

Male chameleons use bright, elaborate visual displays to flaunt their good genes--the more varied and conspicuous the patterns, the more attractive and healthy they appear to potential mates. They use dull grays and browns to signal submission when their courtship attempts are rebuffed or when they are defeated in combat.

In females, a change of color can act as a signal to attract mates or to indicate pregnancy.