Gradesaver's analysis of the final chapter sums this up nicely. Gradesaver's complete guide to The Island of Dr. Moreau can be found at the end of this excerpt;
"In Chapter XXII, Wells reaches the conclusion of his exploration of the barrier between man and animal. The examples Wells uses are significant. For instance, Prendick compares preachers giving sermons with the Ape Man having one of his "Big Thinks," those occasions when the Ape Man discovered a new word but did not understand it and merely gabbled about it. Here Wells seems to put religion on the level of the animals rather than raising it to the level of transcendence that most of his neighbors would do. Now that Prendick has returned to civilized England, he cannot fully reconcile the world around him with the one he left behind on the island. He can no longer distinguish between men and Beast Men. He finds the bestiality in people immediately and unnervingly clear. The pull downward can easily be felt. What, other than self-assertion of one's own agency, provides the upward pull into something more, rather than something less, than mere humanity? Is astronomy going to do the job? The upper boundary of humanity is hardly explored, since this book is about our lower boundary.
Back in the world of technology, Prendick is awash in a London that humans have built to improve their lives. Prendick has learned that the manipulation of nature without attention to the consequences can spell doom, like it did on the island. How many inventions in London are hurting rather than helping mankind?"