National Geographic : 2004 Nov
Evolution is a beautiful concept, MORE CRUCIAL to medical science, and to our heard of Charles Darwin, and of a vague, somber notion about struggle and survival that some times goes by the catchall label "Darwinism." But the main sources of information from which most Americans have drawn their awareness of this subject, it seems, are haphazard ones at best: cultural osmosis, newspaper and magazine ref erences, half-baked nature documentaries on the tube, and hearsay. Evolution is both a beautiful concept and an important one, more crucial nowadays to human welfare, to medical science, and to our understanding of the world than ever before. It's also deeply persuasive-a theory you can take to the bank. The essential points are slightly more complicated than most people assume, but not so complicated that they can't be compre hended by any attentive person. Furthermore, the supporting evidence is abundant, various, ever increasing, solidly interconnected, and eas ily available in museums, popular books, text books, and a mountainous accumulation of peer-reviewed scientific studies. No one needs to, and no one should, accept evolution merely as a matter of faith. Two big ideas, not just one, are at issue: the evolution of all species, as a historical phenomenon, and natural selection, as the main mechanism causing that phenomenon. The first is a question of what happened. The sec ond is a question of how. The idea that all spe cies are descended from common ancestors had been suggested by other thinkers, including Jean Baptiste Lamarck, long before Darwin published The Originof Species in 1859. What made Dar win's book so remarkable when it appeared, and so influential in the long run, was that it offered a rational explanation of how evolution must occur. The same insight came independently to Alfred Russel Wallace, a young naturalist doing fieldwork in the Malay Archipelago during the late 1850s. In historical annals, if not in the pop ular awareness, Wallace and Darwin share the kudos for having discovered natural selection. The gist of the concept is that small, random, heritable differences among individuals result in different chances of survival and reproduc tion-success for some, death without offspring for others-and that this natural culling leads to significant changes in shape, size, strength, armament, color, bio- "a L7Pt 4-. chemistry, and behavior among the descendants. Excess population growth drives the competitive struggle. Because less suc cessful competitors pro duce fewer surviving off spring, the useless or neg ative variations tend to disappear, whereas the useful variations tend to be perpetuated and grad ually magnified through out a population. In an 1837 notebook Darwin sketched his favorite metaphor: a tree of life (left), its twigs as species. Then, believing no one should speculate aboutspecies "who has not minutely describedmany," he spent eight years classifying barnacles(above). By 1854 he was known as a barnacle expert-though not yet an evolutionist. CAMBRIDGEUNIVERSITYLIBRARY(LEFT);ENGLISHHERITAGEPHOTOGRAPHIC LIBRARY, DOWNHOUSE.KENT .. ....