If the intelligent-design side in the evolution debate doesn’t receive the support you might expect from people who should be allies, that may be because they haven’t grasped why the whole thing matters so urgently. I got an email recently from a journalist whom I’d queried on the subject. “All told, I’m on the ID side of the debate,” he wrote, “but it isn’t a pressing interest for me.”

Anyone who similarly doesn’t quite “get it” should read our friend and colleague Wesley J. Smith’s new and important book on the animal-rights movement, A Rat Is a Pig Is a Dog Is a Boy. If you follow conservative journalism, you’ve likely heard about the book from the contentious deliberation it has received in National Review and on NR‘s website. This started with a review by speechwriter Matthew Scully, similarly a friend and a gifted polemicist. Scully is the vegetarian and champion of animals who, for the 2008 Republican convention, wrote the best speech ever given by that great white hunter, Governor Palin.

As a reviewer for Wesley Smith’s book, Matthew Scully was a surprising choice. Scully’s own book, Dominion: The Power of Man, the Suffering of Animals, and the Call to Mercy, received a wounding review in The Weekly Standard some years back from none other than Wesley Smith and it comes in for criticism again in Smith’s book. I can’t understand NR‘s decision to match these two valued friends of the magazine against each other. Matthew wrote, I am sorry to say, a distorting and unfair review of Wesley’s book, to which NR then let Wesley reply, generating additional discussion on the website but less illumination than the subject deserves.

So let’s highlight Smith’s contribution to public understanding of why the Darwin debate matters. His recounting of terrorist and other heinous acts by animal-rights extremists (even grave-robbing!), his exploration of the wicked views of “personhood” theorist Peter Singer, author of A Darwinian Left and the manifesto Animal Liberation — these tell us about the leading edge of what you might call the animalist view, equating humans with animals.

Professor Singer, bioethicist at Princeton University, assesses the worth of an individual living creature by cognitive measures — rationality and self-consciousness. Merely being human confers no special right to life on a creature. In Singer’s hands this idea become a license for murder:

A chimpanzee, dog, or pig…will have a higher degree of self-awareness and a greater capacity for meaningful relations with others than a severely retarded infant or someone in a state of senility. So, if we base the right to life on these characteristics, we must grant these animals a right to life as good as, or better than, such retarded or senile human beings.

By Singer’s calculation, a healthy adult pig has a stronger claim on our protection than a newborn human infant or a human adult suffering from Alzheimer’s disease. Killing a human “non-person” would be no weightier an act than snuffing out a mackerel. Practically speaking, if killing a hemophiliac infant could be shown to benefit a healthy infant, measuring the comparative prospect of each for a “happy” future, then Singer would approve murdering the baby with hemophilia. He would have us employ human non-persons in medical experiments before we use healthy animals.

Obviously, these are monstrous views, sustainable by an otherwise decent person only in the kind of privileged academic setting where scholars live and think in isolation from reality. Unfortunately, it’s precisely the philosophical foundations of decency that are undermined by the Darwinian perspective. If taken deeply to heart, Darwinism erases the distinction, the right of protection, that a human being earns simply by being human. After all, there’s nothing special about belonging to our species over any other. All the species are part of a continuum of life bubbling up from history without guidance, purpose or meaning.

The respect in which such ideas are held in prestige society can’t help but have a morally corrosive effect that trickles down and outward to the rest of the culture. When they are honest with themselves, Darwinists admit this. In his book, Smith quotes Richard Dawkins, who entertains a fond daydream in which scientists find a living human/chimp hybrid, able to breed with both species and thus finally proving that human beings are just another kind of animal:

We need only discover a single survivor, say a relict Australopithecus in the Budongo Forest, and our precious system of norms and ethics could come crashing about our ears. The boundaries with which we segregate our world would be shot to pieces.

Smith is at his very best as he spells out the ethical implications of blurring the human-animal distinction. Not all living things can be valued as equally precious and deserving of life. There has to be some kind of a scale on which creatures and their claims to protection are measured. If being human confers no merit, what does?

Say we discard the Biblical idea that the human countenance bears a divine stamp, the image of God. Then the standards advanced by Peter Singer seem entirely plausible. Moral value, writes Smith, would accordingly be based on the “capacities of each individual.” Such a “standard would obliterate universal human rights.” Smith cites Mortimer J. Adler, who explained what could all too easily follow from a society’s decision to cast off human exceptionalism:

Why, then, should not groups of superior men be able to justify their enslavement, exploitation, or even genocide of inferior human groups, on factual and moral grounds akin to those that we now rely on to justify our treatment of the animals we harness as beasts of burden, that we butcher for food and clothing, or that we destroy as disease-bearing pests or as dangerous predators?

If humans are not exceptional by virtue of being human — perhaps the ultimate take-home message of Darwinism — then the door is open not only to indecency but far worse.