At the Water’s Edge
In AT THE WATER’S EDGE: MACROEVOLUTION AND THE TRANSFORMATION OF LIFE, his first book, science journalist Carl Zimmer presents the theories and discoveries regarding the evolution of air-breathing, land-traveling tetrapods (four-limbed animals) from gilled water animals and the later return of some descendants of these tetrapods to the water. His subject is macroevolution, the development of new species over long periods of time. Macroevolution is distinguished from microevolution, the small changes from one generation to the next produced by natural selection.
From extensive research and interviews with cutting-edge scientists in a number of fields, Zimmer pieces together the picture of how land animals evolved from fish. Then, he traces the probable evolution of cetaceans, the sea-going mammals that include whales and dolphins, from wolf-like mammals of fifty million years ago.
Zimmer offers exaptation and correlated progression, two key terms in contemporary evolutionary thinking that are unfamiliar to most general readers, as the central concepts of macroevolution. Exaptation is an evolutionary change produced by adapting to one environmental challenge that happens to prepare a species for another, unrelated environmental challenge. Thus, air-breathing lungs, essential to life on land, may have originally developed to give fish more stamina in pursuing prey. Correlated progression refers to the influence of evolving body parts on one...
(The entire section is 321 words.)
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