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originally categorized all the creatures he found in the Burgess Shale as a part of the recognized phyla or body plans of today. But in the late 1960s, Harry Blackmore Whittington, a paleontologist at Cambridge University, reopened Walcott’s excavation to take another look. As at the Capitan Reef at Guadalupe National Park, these glorious remnants of past life were entombed in the crest of a mountain, but they had once inhabited an ancient sea. The residents of this ocean community had been caught by mudslides, which preserved their bodies in ghostly detail as flattened images in thin layers of shale.
    They were an odd bunch, mostly small but truly varied and exotic: Opabinia had five eyes and a long, flexible trunk tipped with a grasping spine. Amiskwia looked like a strange seal with a rattlesnake’s head. Anomalocaris had underwater wings, shrimp tails for arms, and a scary mouth with a ring of sharp teeth for cracking the bodies of scorpions, spiders, and shrimp. Wiwaxia had a series of spines projected in two rows along its back, looking like a bear trap ready to be sprung. And last but not least, there was Pikaia , a worm an inch and a half long—man’s early ancestor.
    The Burgess is our best example of the Cambrian explosion, a period during which life jumped from a simple and not too varied existence to the ancestors of the fullest complexity of nature we’ve seen on the planet. The Cambrian explosion perplexed Charles Darwinbecause it offered another refutation of his conception of evolution as a slow and steady progression. Here, life quite suddenly made an enormous leap.
    The development of vision during the Cambrian was one of the great inventions of nature that may have helped ignite the Cambrian explosion, transforming the behavior of all living creatures. It put prey at a whole new level of desperation. Predators could better spot and chase prey. This led to the evolution of shells and the tough exterior skeletons of crustaceans, giving prey a chance at survival. It also provided a much greater likelihood that these creatures would appear as fossils in the rock record because those tough exteriors survived time.
    Movement was another one of nature’s great inventions, but appears to have shifted gears in importance after the Permian mass extinction 250 million years ago. Life in the Permian oceans was largely anchored to the bottom. Lampshells, sea lilies, and shellfish filtered food from the water, a meager though lazy way to make a living. But after the Permian extinction, things that moved dominated the animal kingdom. This new skill buffered life from sudden change in the environment, allowing it to develop.
    But another important aspect was that movement led to complexity. Nature was more diversified after the Permian. Rather than a handful of species that dominated the landscape, with the rest left to eke out a living, multiple species began to abound and thrive in conjunction with each other. The number of species living together increased dramatically in the fossil record and laid the foundation for the world we live in today.
AFRICAN SOJOURN
    Animal life has grown quite larger and more complex since the Cambrian explosion. To see evolution at work I visited the Ngorongoro Conservation Area in Tanzania, Africa. Man has devastated large animal populations in most places on earth, but in Africa these twoevolved simultaneously and wildlife adapted to keep their distance. Nowhere on earth except in Africa are there so many large animals, though even here they are subject to human voracity. Evolution, however, is helping some animals adapt to man by shedding their tusks and horns.
    To view this firsthand I traveled one summer day with Joseph Masoy, a smiling, husky Tanzanian, who commanded his Toyota Land Cruiser over bumpy African roads to get into Ngorongoro Crater, the relic of an ancient volcano that was once filled with lava but is now filled with African wildlife. Seated with me in the truck