Disappearing, Reappearing Wings

A new stick insect study shows that even the theory of evolution evolves.

Science isn't always simple, but until recently, evolutionary theory followed an easy formula: when constructing a family tree, the path that requires the fewest number of evolutionary changes is generally correct. For instance, complex structures like an insect's wing are likely to have evolved only once.

However, a surprising new study of phasmids - the stick and leaf shaped insects famous for their ability to blend into their environment - has forced this theory to evolve. While analyzing the DNA of 37 different phasmid species, Michael Whiting and his team from Brigham Young University found that the first stick insect, which appeared 300 million years ago, had already lost its wings and that its descendants re-evolved the structures at least four separate times.

Stick insects are herbivores that rely on their masterful camouflage skills to avoid predators. Because of this, the first phasmids may have faced evolutionary pressure to stop expressing their wing-creating genes. At least 50 million years later, some phasmid species began to re-develop wings. Whiting believes that a single gene may be responsible for switching on or off the growth of these complex structures, since separate studies indicate that a master gene called Pax-6 might control the development of eyes in all animals that have them.

Last Update 01/223/2003

Phasmid species from Barro Colorado Island (Panama)
Photo: Dr. Llloyd Glenn Ingles, CAS Special Collections

Stick insect appearing as algae mimic at Las Cruces Biological Station, San Vito, Costa Rica.
Photo: Gail Hewson-Hull.