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Chapter 1: Introduction
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Chapter 1 Introduction Evolution is so clearly a fact that you need to be committed to something like a belief in the supernatural if you are at all in disagreement with evolution. It is a fact and we don’t need to prove it anymore. Nonetheless we must explain why it happened and how it happens. —Ernst Mayr, Harvard University The theory of evolution is one of the most successful in all of science. Its predictions have been verified countless times since the publication of Charles Darwin’s On the Origin of Species in 1859. As we will see, the evidence is so stunning and complete that we are confident in saying that descent with modification is an observed fact. Further, the modern theory of evolution, also called the modern synthesis, combines Darwin’s concept of descent with modification with the theory of genetics.The modern synthesis accounts for the observed facts better than any other theory. Biological, or organic, evolution refers to descent with modification, or changes among organisms over generations.The unit of evolutionary change is the population, not the individual. But change begins with the molecules and molecular interactions of genetic material in an individual and ultimately develops in individuals physical or behavioral traits that differ from their ancestors’. Because the change is in the genetic material of the individual, that change is heritable. In other words, if the individual reproduces successfully , that change is passed on to its offspring. Ultimately, the change may become common within the population of which the original individual was a member. At this point, we conclude that the population has evolved, because it has experienced a widespread biological change. Indeed, the definition of evolution is the widespread change of a genetic trait within a population. Finally, if the population evolves so far that it cannot normally interbreed with the ancestral population, we say that a new species has evolved. 3 CH001.qxd 3/26/09 5:24 AM Page 3 Why Is Evolution Important? Evolution is critically important today,yet many people—especially in the United States—reject it, often on religious grounds.Why is it so important, and why do so many people reject it?We will answer those questions in order. The world that the next generation inherits will be shaped in large part by our understanding of evolution or, perhaps, by our lack of understanding. For example, when antibiotics were discovered, many physicians wrongly assumed that bacterial diseases would become a thing of the past. Only a few prescient thinkers recognized that bacteria would evolve resistance to antibiotics and warned against overusing them. Such warnings went unheeded even though a penicillin-resistant strain of the bacterium Staphylococcus aureus, which can cause skin infections, meningitis (a brain disease), pneumonia, and septicemia (blood poisoning), was discovered within four years of the first mass production of the very first antibiotic. Indeed, today, a number of harmful bacterial species, including those that cause tuberculosis and childhood ear infections, are resistant to at least one widely prescribed antibiotic. These organisms have evolved into their new, antibiotic-resistant forms by random genetic mutation, the process that provides the raw material for natural selection. Plasmodium, the parasite that causes malaria, has likewise grown resistant to the early treatment, quinine, and its later derivatives. Because there are only a limited number of ways to kill bacteria (without also killing the host), we may have few remaining opportunities to develop new, effective antibiotics. If public health policy reflected a keen understanding of evolution, we would stop prescribing antibiotics for diseases against which they are ineffectual, and we would not administer them routinely to livestock and fowl, as we do now. Similarly, many insects and noxious weeds have become resistant to insecticides and herbicides, and farmers have to use more and stronger chemicals to control them. In addition, the mosquitoes that carry malaria have become resistant to insecticides. Besides mosquitoes, many species of lice, ticks, bedbugs , and fleas, not to mention cockroaches, have become resistant to one or more insecticides. Many of these insects transmit diseases to humans. Any evolutionary biologist could have predicted insecticide resistance. Erosion of Genetic Diversity An evolutionary biologist would also be greatly concerned about the loss of diversity among our food crops and the lack of diversity in our agricultural fields. Today, for example, farmers in developed countries plant only a relatively few varieties of wheat.They used to plant hundreds of varieties of apple; now we commonly see less than a dozen...