Among the pagan practices vanquished by early Christians was infanticide. As Christianity fades in the West, so do our defenses against infanticide in all its grisly forms.

Since its beginning, the pro-life movement has argued that the logic that justified abortion-on-demand could, at some point, be also used to justify infanticide.

And for just as long, defenders of abortion rights have rolled their eyes, literally and figuratively, regarding our concerns about the slippery slope of killing innocents as “kooky” and “alarmist.”

But then in 1997, Steven Pinker, one of the leading lights of what’s known as “evolutionary psychology,” published a piece in the New York Times that argued for the “naturalness” of infanticide. While not denying that under modern conditions, “Killing a baby is an immoral act,” it was a kind of triage for our not-so-distant relatives to separate those likely to survive from those unlikely to survive.

More importantly, as Pinker memorably put it, the genes that shaped that behavior are still present within the human race today. “A new mother . . .” he said, “will first coolly assess the infant and her situation and only in the next few days begin to see it as a unique and wonderful individual.”

To which the late Michael Kelly, who had previously dismissed any link between abortion and infanticide, replied “Yes, that was my wife all over: cool as a cucumber as she assessed whether to keep her first-born child or toss him out the window.”

While Kelly may have won the battle of wits two decades ago, it may be that Pinker is winning the long-term war of ideas.

Fordham ethicist Charles Camosy recently noted in Commonweal magazine that what was shocking to Kelly two decades ago is becoming normal today. Far from being “alarmist” or “kooky,” there’s a straight line between our ideas about abortion and our increasing willingness to countenance the idea of infanticide.

As Camosy points out, if “being a living organism of the species Homo sapiens,” as a human fetus certainly is, doesn’t confer “a moral or legal right to life,” what does? The “most reasonable” answer is “self-awareness and the ability to care about one’s own life.” But since newborn infants, like fetuses, don’t meet this criteria, “infanticide does not violate a person’s right to life.”

Now, Camosy doesn’t believe any of this. He’s merely explaining “the surprisingly compelling” link between abortion and infanticide.

Just in the past decade, this lethal logic has made its way into government and hospitals. In 2004, the University Medical Center Groningen in the Netherlands adopted a protocol to allow for the killing of infants whose condition was deemed “hopeless.” Now such a killing is technically illegal under Dutch law, which reserves euthanasia for those twelve and older, but no physician who follows this protocol has ever been prosecuted.

And consider the recent cases of Charlie Gard and Alfie Evans, whose parents were denied permission to leave Britain in search of further treatment for their ailing sons. As Camosy writes, “Their lives were deemed (by doctors with no special moral training or authority) to be without dignity; their suffering deemed to be pointless.”

Camosy’s logic and his use of the word “dignity” points to the ultimate source of creeping infanticide—the West’s rejection of Christianity. The idea of human dignity is one of Christianity’s great gifts to Western civilization.

The Christian vision of humanity is the basis for our ideas about equality and human rights. As Eric Metaxas recently said on BreakPoint, Christianity is why we believe the poor and the weak have intrinsic value, something the ancient Greek and Roman pagans would have scoffed at.

And so do people like Pinker. He calls the idea of human dignity “stupid” In his thinking, “human dignity” should be replaced with “autonomy,” and therefore personhood can only be established after birth.

As it turns out, our concerns weren’t that kooky after all.