Creationists sometimes argue that the idea of evolution must remain hypothetical because “no one has ever seen evolution occur.” This kind of statement also reveals that some creationists misunderstand an important characteristic of scientific reasoning. Scientific conclusions are not limited to direct observation but often depend on inferences that are made by applying reason to observations. Even with the launch of Earth-orbiting spacecraft, scientists could not directly see the Earth going around the Sun. But they inferred from a wealth of independent measurements that the Sun is at the center of the solar system. Until the recent development of extremely powerful microscopes, scientists could not observe atoms, but the behavior of physical objects left no doubt about the atomic nature of matter. Scientists hypothesized the existence of viruses for many years before microscopes became powerful enough to see them.
Thus, for many areas of science, scientists have not directly observed the objects (such as genes and atoms) or the phenomena (such as the Earth going around the Sun) that are now well-established facts. Instead, they have confirmed them indirectly by observational and experimental evidence. Evolution is no different. Indeed, for the reasons described in this booklet, evolutionary science provides one of the best examples of a deep understanding based on scientific reasoning.
This contention that nobody has seen evolution occurring further ignores the overwhelming evidence that evolution has taken place and is continuing to occur. The annual changes in influenza viruses and the emergence of bacteria resistant to antibiotics are both products of evolutionary forces. Another example of ongoing evolution is the appearance of mosquitoes resistant to various insecticides, which has contributed to a resurgence of malaria in Africa and elsewhere. The transitional fossils that have been found in abundance since Darwin’s time reveal how species continually give rise to successor species that, over time, produce radically changed body forms and functions. It also is possible to directly observe many of the specific processes by which evolution occurs. Scientists regularly do experiments using microbes and other model systems that directly test evolutionary hypotheses.
Creationists reject such scientific facts in part because they do not accept evidence drawn from natural processes that they consider to be at odds with the Bible. But science cannot test supernatural possibilities. To young Earth creationists, no amount of empirical evidence that the Earth is billions of years old is likely to refute their claim that the world is actually young but that God simply made it appear to be old. Because such appeals to the supernatural are not testable using the rules and processes of scientific inquiry, they cannot be a part of science.