Catching evolution in action

A hundred years ago Charles Darwin’s theory of evolution by natural selection was taught as the foundation of biology in public schools throughout the United States. Then something happened. In the 1920s, conservative religious groups began to argue against the teaching of evolution in our nation's schools. Darwinism, they said, contradicted the revealed word of God in the Bible and thus was a direct attack on their religious beliefs. Many of you will have read about the 1925 Scopes "monkey trial" or seen the move about it, Inherit the Wind. In the backwash of this controversy, evolution for the first time in this century disappeared from the schools. Textbook publishers and local school boards, in a wish to avoid the dispute, simply chose not to teach evolution. By 1959, 100 years after Darwin's book, a famous American geneticist cried in anguish, "A hundred years without Darwin is enough!" What he meant was that the theory of evolution by natural selection has become the central operating concept of the science of biology, organic evolution being one of the most solidly validated facts of science. How could we continue to hide this truth from our children, crippling their understanding of science? In the 1970s, Darwin reappeared in our nation's schools, part of the wave of concern about science that followed Sputnik. Not for long, however. Cries from creationists for equal time in the classroom soon had evolution out of our classrooms again. Only in recent years, amid considerable uproar, have states like California succeeded in reforming their school curriculums, focusing on evolution as the central principle of biology. In other states, teaching Darwin remains controversial. While Darwin’s proposal that evolution occurs as the result of natural selection remains controversial in many local school boards, it is accepted by practically every biologist who has examined it seriously. In this section, we will review the evidence supporting Darwin’s theory. Evolutionary biology is unlike most other fields of biology in which hypotheses are tested directly with experimental methods. To study evolution, we need to investigate what happened in the past, sometimes many millions of years ago. In this way, evolutionary biology is similar to astronomy and history, relying on observation and deduction rather than experiment and induction to examine ideas about past events. Nonetheless, evolutionary biology is not entirely an observational science. Darwin was right about many things, but one area in which he was mistaken concerns the pace at which evolution occurs. Darwin thought that evolution occurred at a very slow, almost imperceptible, pace. However, in recent years many case studies of natural populations have demonstrated that in some circumstances evolutionary change can occur rapidly. In these instances, it is possible to establish experimental studies to directly test evolutionary hypotheses. Although laboratory studies on fruit flies and other organisms have been common for more than 50 years, it has only been in recent years that scientists have started conducting experimental studies of evolution in nature. To conduct experimental tests of evolution, it is first necessary to identify a population in nature upon which strong selection might be operating (see above). Then, by manipulating the strength of the selection, an investigator can predict what outcome selection might produce, then look and see the actual effect on the population. Part VI