Actually, it's just a theory
Another way "fact" is used is to refer to a certain kind of theory, one that has been so powerful and productive for such a long time that it is universally accepted by scientists. When scientists say evolution is a fact in this sense, they mean it is a fact that all living organisms have descended from a common ancestor (or ancestral gene pool) [8] in that predictions made by the theory have consistently been supported by empirical observations.[9] This implies more tangibly that it is a fact that humans share a common ancestor with all living organisms."
From wikipedia
