IN THE BLINK OF AN EYE

The Cambrian period saw the first proliferation of complex life on earth, and herewith is the fascinating argument that the development of vision triggered “evolution's big bang.”

Parker (Zoology/Oxford) takes a roundabout route to this destination, touching on a wide variety of disciplines. Cambrian fossils, such as those of the Burgess Shale, are the first to preserve solid body parts—the armor and claws of the alien-looking life forms that apparently sprang out of nowhere some 543 million years ago. Parker vividly describes his visits to several key Cambrian fossil sites, and the kind of information fossils can be made to yield. A long unanswered question is the coloration of extinct animals, a feature not readily determined from fossils. Comparison of two groups of marine crustaceans, one of which uses flashes of light as a mating signal, led to the discovery of minute body parts capable of functioning as diffraction gratings—a startling biological anticipation of high tech. Parker then undertook microscopic examination of Cambrian fossils, uncovering quite similar structures preserved in ancient beetles, sea creatures, and even some members of the Burgess fauna. This recovery of vanished colors from physical structures preserved in fossils is in itself a breakthrough, but Parker does not stop there. Color implies the presence of eyes to see it; a careful examination of the eyes of living creatures clarifies the question (which vexed even Darwin) of how eyes evolved. Trilobites, one of the characteristic Cambrian animals, appear to have been the first creatures capable of clear vision. Parker's conclusion, that the presence of eyes indicates the evolution of an active hunting lifestyle among Cambrian creatures, is both convincing and surprisingly fresh. Parker's writing skills are not quite up to the level of his science, but the subject matter is so compelling that few readers are likely to object.

Cutting-edge science, highly recommended.