The Nature of a Scientific “Theory.”
Since 1859, scientists have corroborated Darwin’s theory countless times. Darwin's theory is thus no longer a “theory” in the popular sense of the term — that is, an “untested or unproven idea.” Evolution is a “theory” in the special scientific sense of a large, organizing concept that has been confirmed so often and so comprehensively that it has acquired a status similar to a scientific “law.” Newton’s “theory of gravitation” and Einstein’s famous “theory of relativity” are similar organizing concepts in science. Darwin’s “theory” [in this sense] is the central idea of modern biology and its fundamental organizing concept.
Steps in Corroboration — The cause of “variation” established.
Gregor Mendel, a Catholic priest and abbot in the Austrian Empire and a contemporary of Darwin, published a ground-breaking but little noticed study of plant hybridization in 1866, that laid the foundation for the science of genetics. Darwin possessed a copy of the journal in which Mendel had published his essay in his private library, but he never read the article. Late in the 19th century, other scholars, such as J. S. B. Haldane, joined Mendel's work on genetics to Darwin's theory to provide a full explanation of "variation" — why offspring of the same parents are not identical — and thus filled a gap in Darwin’s own knowledge. We now understand that the science of genetics provides an explanation for Darwin’s “variation.”
The discovery of the structure of DNA in 1956 was further confirming evidence of Darwin’s general theory. The Human Genome Project (1990 to 2003), an international scientific effort to identify and understand the functions of our approximately 20,000 to 25,000 genes, has provided overwhelming confirmation of our evolution and our relatedness to other life.