Isn’t evolution supposed to be part of biology?
Evolution has found its true home in other sciences such as literary criticism and politics. It has meaning for such as Bill Clinton whose objective on earth is to accelerate the pace of societal evolution. For biology it is mainly an acknowledgement that this species is close to that species and that species is close to the next one and so on. A mechanism that might produce those differences has been proposed now and then but that is not important. The important thing is the links and differences between species, which allows a method of classification of the many, many species which would otherwise hardly be catalogable or nameable. It’s part of how we might make some sense of what we see. Recall that Aristotle, the botanist of antiquity, had a garden of his extensive collection of species that was so extensive even he knew the names of only about 25% of them. He would have been ecstatic to have a system such as evolution so he could organize them more systematically.
A small part. It’s mostly found in the human sciences.