Vegetarian philosophy and Darwin's theory of evolution informed numerous authors in the Victorian era. Horror elements of The Island of Doctor Moreau have their roots in these ideas.
Vegetarian movements were popular during Wells' lifetime, and although some based their philosophies off health benefits and/or the prevention of cruelty, others employed Darwinistic reasoning: if humans share common ancestry with the animals, then eating animal flesh is tantamount to cannibalism. In 1895, Arnold Frank Hills, president of the Vegetarian Federal Union, said, “[c]annibalism is the natural consequence of a carnivorous dietary-to eat a man is the logical conclusion of devouring a sheep” (1). This sheep/man dichotomy is brought up early in the novel. It is no accident that Prendick's first meal after being spared from eating his shipmates is a disgusting one. He is given iced blood and boiled mutton (notorious for its foul stench). The meal is calculated to magnify the readers' revulsion, just as they would be repelled by cannibalism.
Moreau is a vegetarian and attempts to enforce vegetarianism on his island. This may seem ironic considering his cruelties, but his rationale has nothing to do with suffering and everything to do with survival. It harkens back to Howard Williams' The Ethics of Diet, the seminal Victorian treatise extolling vegetarianism. In it, the degeneration of society is blamed upon wholesale slaughter and the eating of meat (2).
Indeed, the micro-society falls apart when it becomes carnivorous. Moreau's creatures begin eating rabbits. Considering the chimeric qualities of Moreau's creatures, eating rabbits is certainly a form of cannibalism. It signals the onset of wholesale slaughter and the civilization's end.
From these examples, one may see how vegetarian philosophy paired with Darwinistic theory are at the core of The Island of Doctor Moreau.
1.
http://www.readperiodicals.com/201010/2168339961.html2.
http://en.wikipedia.org/wiki/Howard_Williams_(humanitarian)