At the Water's Edge : Macroevolution and the Transformation of Life

Offers an examination of the twin evolution of the earliest marine life--one branch that came ashore and evolved into turtles, dinosaurs, and eventually humans; and the other that crept back into the water and become whales, dolphins, and other underwater life

One of the hallmarks of life is change. In his first book, Zimmer, a senior editor and feature writer at Discover magazine, has chosen to explicate two of the biggest examples of organic evolution the Earth has ever seen. He starts by describing how fish, beginning between 350 and 400 million years ago, evolved into creatures who crawled out of the water and, eventually, into terrestrial mammals able to breathe air, withstand the pressures of gravity and move about without the aid of water. He then turns his attention to how, 40-50 million years ago, some well-adapted terrestrial mammals went back into the sea and, over time, gave rise to whales, porpoises and their marine relatives. Zimmer shows that the transformation back to aquatic life?without the luxury of gills, fins and the host of additional adaptations that make fish so successful?was an amazing evolutionary feat. Zimmer treats the controversy surrounding the mechanism of macroevolution only cursorily: he opts not to take a position in the conflict between the proponents of punctuated equilibrium and the advocates of gradualism. But he makes up for that lack with his gripping account of how scientists work. By accompanying scientists into the field, visiting them in their laboratories and conducting extensive interviews with them, Zimmer communicates the excitement of cutting-edge scientific research and fieldwork. More than just an informative book about macroevolution itself, this is an entertaining history of ideas written with literary flair and technical rigor. Line drawings and diagrams throughout.
Copyright 1998 Reed Business Information, Inc.

Points to Zimmer, a senior editor at Discover magazine, for tackling unplowed ground in popular paleontology: no less than the movement of life from sea to land (over 350 million years ago) and the later reverse migration as land mammals returned to the sea. These transitions are dubbed ``macroevolution''--big changes, as opposed to the smaller changes of microevolution. The bare bones of current theory has it that we are descended from lobe-finned fishes. During a wet period when plants were creeping toward the water's edge and swamps abounded with life, these fish developed fins with fingers and toes to maneuver on muddy bottoms and pick at plant life while staying mainly in the water. But one thing led to another, and more land-lubbering species emerged. The one thing Zimmer emphasizes is the role of ``Hox'' genes, which control major events in embryogenesis, such as the shape of the basic body pattern and the formation of limbs from tissue ``buds.'' A mutation in timing or patterning of Hox genes can do wonders for changing form and function. The reverse transition from land to sea is an equally complex story and maybe even more controversial. It involves what Zimmer describes as a misfit group of hoofed, long-snouted, carnivorous predators called ``mesonychids'' drawn to the sea for the rich herring and other catches. Subsequent changes over a few million years involved loss of fur, hips, and lower limbs and development of fins and fluke and other essentials of life in the depths. Zimmer uses the latest cladistic diagrams to plot the species splits and changes over time--pointing out that they are at odds with molecular geneticists' DNA analyses, which would have hippos as whales' closest living relatives. Don't hold your breath waiting for resolution on that score. But do credit Zimmer with this scholarly disquisition on two of evolution's most absorbing transformations. -- Copyright ©1998, Kirkus Associates, LP. All rights reserved.

Tracing the ancestry of early land animals back to fish and of whales back to later land animals has long required strong faith in Darwinian doctrine, largely unsupported by biological or fossil evidence. The recent discovery of that long-sought evidence--paleontological, genetic, and anatomical--makes a fascinating story, which Zimmer unfolds as a tale of high-stakes scientific sleuthing. Thanks to marvelously lucid writing, readers can decipher clues (a fossil skull from Pakistan, a DNA study in Brussels, a statistical brain dissection at UCLA) right alongside some of the world's greatest researchers, starting with Darwin himself. While steering clear of technical minutiae, Zimmer allows readers to wrestle with theoretical problems that have long attracted strong minds (and combative personalities) to evolutionary biology. A worthwhile addition to any public library's general science collection. Bryce Christensen

Zimmer examines the phenomenon of macroevolution (global evolution across hundreds of millions of years) by looking at sea-to-land evolution, then the much later land-to-sea processes that led to ocean mammals.
Copyright 1999 Reed Business Information, Inc.