KNOWLEDGE YOU CAN USE

KNOWLEDGE YOU CAN USE

Evolution What It Is and What It Is Not…

Misconceptions about evolution and how it occurs can arise from misunderstandings about subtleties in the process, from incomplete or erroneous accounts of evolution in schools and the media, and from purposeful attempts to interfere with the understanding of evolution.

• Misconception: Evolution is a theory about the origin of life. Clarification: Although scientists are interested in (and are investigating) how life began, evolutionary biology is focused on the processes that occurred (and still occur) after life began, including those responsible for the diversification and branching of species and those adapting populations to their environments.
• Misconception: Evolution is not observable or testable. Clarification: Evolution is both observable and testable. Long-term, controlled, and replicated laboratory experiments on many species have demonstrated evolution (see an example in Section 8-1) and speciation (formation of new species). Numerous studies of natural populations have also documented evolution taking place (see Section 8-13). And, as in astronomy and geology, sophisticated hypothesis testing can be done using observations in the natural world.
• Misconception: Evolution is only a theory and hasn’t been proved. Clarification: This misconception stems from confusion between the colloquial definition of a theory as a “guess” or “hunch” and the scientific definition of a theory as an explanation, based on many lines of evidence, that generates and supports predictions and is tested in many ways (see Section 1-10).
• Misconception: Individuals evolve (and are “trying” to adapt). Clarification: Natural selection can lead to populations of organisms adapted to their environment (see Sections 8-12 and 8-16). But the process does not involve “trying” to adapt—it is simply a consequence of some individuals passing on their genes at a higher rate than individuals carrying alternative versions of those genes, and it is the population rather than any one individual that changes over time (see Section 8-11).
• Misconception: Evolution is goal-oriented and leads to progress and “optimal” solutions. Clarification: Alleles that make it impossible for the individuals carrying them to live in a particular environment are weeded out of the population. But this is not the same as creating perfect or optimal organisms. Rather, the traits and features of organisms that increase in frequency within a population are simply those that cause the organisms carrying them to leave more descendants than are left by individuals with alternative traits (see Sections 8-9 and 8-16). As the environment changes, so do the traits that are most fit. Several factors can prevent populations from becoming better adapted to a particular environment (see Section 8-13).
• Misconception: There are no transitional fossils; the gaps in the fossil record disprove evolution. Clarification: Because fossils are formed only under a narrow range of environmental conditions, biologists do not expect to find all transitional forms, so the gaps do not disprove evolution. Numerous transitional fossils have been found, including those between dinosaurs and modern birds, and those between whales and their terrestrial mammalian ancestors (see Section 8-18).
• Misconception: The theory of evolution says that life originated, and evolution proceeds, randomly, by chance. Clarification: Although chance is one element of evolution—there is a random element to the generation of mutations, for example—many non-random factors are central to how evolution proceeds. For example, the differential reproductive success of some variants—such as bacteria with antibiotic-resistance genes—that leads to natural selection is not random (see Section 8-12).
• Misconception: Most biologists have rejected evolution. Clarification: All modern theories of science are continually tested, verified, and modified as new and deeper understandings of the natural world emerge. That is how science works. The presidents of the National Academy of Sciences, the American Association for the Advancement of Science, and the National Science Teachers Association recently wrote a joint statement saying that “evolutionary theory has stood the test of time in serving as the most comprehensive scientific explanation for the diversity of life on Earth and it is accepted by the overwhelming majority of scientists.” There have been no credible challenges to the basic principles of evolution and how it proceeds.