George Pannel, age 12, of Phoenix, Ariz., for his questions
What makes a chameleon change color?
Lets not confuse the genuine Old World chameleon with the anole, who is a pretty lizard of our own southwest, sometimes sold as a chameleon. Both are lizards and both can change color to some extent, but the true chameleon is the champ. He is far from pretty and could be mistaken for an infant bugeyed monster. His big eyes are mounted on cone shaped turrets and he can swivel them this way and that. In fact, he can swivel one to survey the view behind him while the other is trained on the foliage above his head.
Altogether there are some 80 of these chameleon cousins living in Africa, Madagascar, the Near .East, certain Mediterranean islands and India. A11 are slow moving insect eaters with long sticky tongues. All can change color from yellow, through green to greyish black, though these color changes do not necessarily match the surroundings,
The color changes occur when light triggers off a response in the chameleons brain and nervous system. Certain cells in the skin swell or shrink. Greatly enlarged under a microscope, these special cells look like layers of colored marbles. The top layer is mostly yellow, the middle layer mostly black and the bottom layer is whitish with black marbles. The color changes are caused by reflections from the whitish layer and by the black marks in the center which shrink or swell.
When a bright light is reflected in the chameleon's eyes, a message is flashed to the black cells and they expand. First they become a solid layer, cutting off any light reflected from the white cells below them. At this point, we see only the cells in the surface layer and the chameleon looks yellow.
The black cells continue to swell, surrounding the yellow cells in black fringes. The chameleon turns blackish grey.
In a dark room, the black cells shrink to tiny dots. We see only the surface cells and the chameleon looks yellow. Sometimes the lower white cells reflect light as blue. This blue light blends with the surface yellow cells to make green and the chameleon seems to be wearing a green skin.
The sensitive responses in the chameleon's brain and nervous system are triggered off by direct light or by light reflected from a pale or dark background. In a dark room he is yellow, in strong sunlight oil a dark or light background he is blackish. Under a sunny blue sky, he is often green.
Our own pretty anole lizard changes from brown to green, though not to match his surroundings. His normal coloring is green, but he has cells of dark pigment in his skin. Strong light makes the dark cells expand and the ahole becomes brown. The same thing happens when he is cold. Under normal conditions the dark cells are tiny dots, too small to alter his natural green coloring.