Evolution As Fact and Theory

Evolution as fact and theory is the basis of a discussion in public and scientific discourse on the fundamental nature of the scientific philosophy and practice within evolutionary biology. The topic is raised by scientists to clarify the nature of these terms in science, responding to the common misconceptions that "evolution is only a theory"; "it is not a fact"; or that intelligent design offers a credible counter "theory". Evolutionary biologists identify evolution as either fact or theory and occasionally as both or neither. Semantic differences between the usage of these terms (fact and theory) in science versus the meanings they convey in common vernacular have led to confusion in public discourse. In the context of creationists' claims, the word "theory" is used in its vernacular meaning as an imperfect fact or an unsubstantiated speculation, and the purported intent is to discredit or reject the scientific credibility of evolution. However, this claim cannot be substantiated.

Evolutionary theory integrates observations from fossils, DNA sequences, systematics, biogeography, and laboratory experiments into a rational explanatory scheme. In this sense, the scientific (as opposed to the vernacular) definition of theory refers to an overarching framework that makes sense of otherwise disconnected observations. Theodosius Dobzhansky, a key contributor to the modern evolutionary synthesis, articulated the unifying power of evolutionary theory in a famous paper entitled: "Nothing in biology makes sense except in the light of evolution".

Scientific theories in evolutionary biology present causal explanations for the observable and measurable phenomena of life on Earth. Natural selection and the neutral theory are examples of theories of evolution. These and other evolutionary theories can be expressed in mathematical terms of population genetics or through rational logic where human reasoning is applied. Since Darwin, the theory of evolution by means of natural selection has not only been expressed mathematically, but has also been rigorously tested and corroborated empirically by convergent scientific evidence. Evolutionary theories continue to generate new testable hypotheses within paleontology, genetics, ecology, and developmental biology.

Facts refer to "events that occur" or "the state of being of things" that can be publicly verified, proven through experiment, or witnessed by direct observation. Facts exist independent of theory or knowledge of them. In science, however, a fact is not a statement of absolute certainty. Scientific knowledge necessarily abandons the concept of absolute certainty to remain consistently conjectural, hypothetical. When referring to or representing facts through theory, scientists (including evolutionary biologists) subscribe to different philosophies, such as scientific realism, materialism, or pragmatism. Accordingly, evolutionary biologists suggest that the scientific method reveals truths about "real nature" that is separate from our thoughts on the matter. That all forms of life on Earth are related by common descent with modification is one of the most reliable and empirically tested theories in science that continues to explain vast numbers of facts in biology.