Is Evolution a Fact or a Theory?
Both. In Darwin's day, and before, many naturalists theorized that living things were somehow related in a manner beyond that of their obvious common differences from non-living matter. These speculations, including those of Darwin, are appropriately termed theories: speculations about nature that were informed by observation and subject to test by additional observations.
Over the years since the introduction of a theory of evolution by Charles Darwin and Alfred Russel Wallace, biologists and geologists have continuously tested the ideas of descent with modification and have obtained no contradictory observations. Indeed, we recognize today that this aspect of biological evolution is not properly a theory at all, it is an observation. This is analogous to the Copernican theory in astronomy. Copernicus initially proposed the theory that the Earth rotates around the Sun, and not viceversa. The innumerable observations consistent with this theory which we have accumulated in the meantime make the assertion that the Earth rotates around the Sun a well established fact.
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