Help with Questions to The Island of Dr. Moreau: Moreau’s idea about transforming animals into humans

Moreau’s idea about transforming animals into humans suggests an acceptance of Darwin’s proposals regarding evolution. How does the story as a whole serve engage the theme of biological transformation, by natural and artificial means? Why is it that Wells chooses to make the Beast Folk gradually regress to bestiality? Are humans constantly fighting the tendency to become like animals, or are we naturally on the way up to something better?