Here, I think this excerpt from Wiker's "Moral Darwinism" book FAR overstates the case as to Darwin being a "disciple" of Epicurus. Darwin is "the most potent formulation of that philosophy [Epicurus] to date?" That is way overstated.
Do we actually know that Darwin was either an explicit fan of, or quoted, Epicurus? We do know that Nietzsche was at least in certain respects a fan of Epicurus, but that Nietzsche was not a fan of Darwin. I have not read deeply into Darwin but my gut tells me that Nietzsche is right on this, and that Darwin probably does not deserve a lot of study by an Epicurean except to note Darwin's development of theories of nature that are not guided by supernatural beings, which is only one aspect of Epicurus.