The Natural History Reader in Evolution

By Niles Eldredge | Go to book overview

PART 5
LIVING FOSSILS

Evolution means "change" to most people. Why, then, in a book on evolution should we be concerned with "living fossils"--creatures that appear not to have changed from their ancestral state for periods of time that seem formidable even in geological terms?

The theory of evolution we have been piecing together so far has as its core the notion of adaptation through natural selection. Darwin succeeded in implanting the concept so well that we came to think of adaptive evolutionary change as inevitable, and not the impossibility nearly everyone believed it to be prior to the appearance of On the Origin of Species. But if change is literally built into the system, how then do we explain these anomalous cases of "arrested evolution," these living fossils who have resisted the irresistible?

Evolution is best thought of as maintenance, modification, and transmission of genetically based information. Modification, the transformation of organismic features and their underlying genes, is only part of the story. There are many reasons why organic features should not become modified, many of which are broached in the following essays. Understanding why evolutionary change does not occur, why things remain stable, is to take us a long way down the path toward understanding how and why change occurs--when it occurs at all.

"Living fossils" is a phrase that actually encompasses a variety of similar, yet slightly different, phenomena. Some biologists see the phrase as devoid of meaning, or at the very least misleading. And it is true that, if what is meant as a definition is that species tend to remain unchanged as the very same species for tens, or even hundreds of millions of years, "living fossils" is an empty concept indeed. But all that is usually meant by the phrase is that some creatures alive today are astonishingly reminiscent of relatives that lived truly long ages ago. Evolution seems to have passed them by, all the while greatly modifying their close collateral kin as time has gone by.

The first three essays set out the details of particular cases of living fossils. Howard L. Sanders recounts the history of discovery of the primitive crustacean Hutchinsoniella macracantha, found living virtually under our noses in Long Island

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