know the truth

Chameleons evolved their famous skin-altering abilities not for camouflage but to communicate quickly with others, a new study suggests.

Scientists have known that the reptiles use color-changing for a variety of purposes: to blend in to the environment, to regulate their body heat, and to send messages to other chameleons.


Instead of vocalizing or using pheromones, chameleons communicate visually by changing the colors and patterns of their skin. Different colors and patterns mean different things—similar to how the colors of a traffic light direct drivers.
"Communication is also partly the function of coloration," Christopher Raxworthy, associate curator of herpetology at the American Museum of Natural History in New York, wrote in an e-mail interview.

One of the world's foremost chameleon experts, Raxworthy has discovered several new species and is actively engaged in protecting chameleon habitat in Madagascar.

Part of his research involves studying what the lizards communicate with each other via changes in their color. He's found that the color shifts often express territorial dominance or unwillingness to mate.

"Males become more brightly marked to advertise their dominance," Raxworthy said. "Females become dark or flash red spots to advertise their hostile response to males or their non-receptive status. Aggressive chameleons may become very dark."

Whatever the color signals mean, the tropical reptiles' unusual ability has earned them a fan base among humans.

Undergraduate college student Chris Anderson edits several chameleon-related Web sites, including the Chameleons! Online E-Zine, while studying biology at Cornell University in Ithaca, New York.

He said chameleons are rightfully considered masters of camouflage, but that people often mistake color change as an effort to blend in when in fact the lizards could be showing signs of stress.

Color Change

According to Anderson, the ability of chameleons to change color stems from special cells called chromatophores found in the upper layers of their skin. These cells are filled with different kinds of pigment.

The lizards have three layers of chromatophores. The deepest layer contains melanophores, which have black pigment. Cellular branches extend from these cells and allow the pigment to flow up to and interact with the pigment in upper layers.

The middle layer of cells, called guanophores, regulate blues shades, and cells in the uppermost layer, called xanthrophores, contain yellow and red pigments.

For example, the brighter colors a male displays, the more dominant he is. So male chameleons can attract a mate or defend their territory by flashing bright colors to each other. To communicate submission or surrender, a male will display drab browns and grays.

Females also use a colorful version of signaling to communicate when they want to reject mates or are pregnant.

But how these traits evolved remained a mystery—until now.

"Basically there's a neurological control mechanism that stimulates the pigments" to move around and cause the chameleon's skin color to change, Anderson explained. Whether chameleons are actively aware of their color changes is an open question, Anderson said. He suspects that the ability to do so is a trait borne out through the process of natural selection.