Hey, did you hear the one about the woman who aborted her kid so she could save the planet?

That's no joke, but Darwin must be chuckling somewhere.

Toni Vernelli was one of two women recently featured in a London Daily Mail story about environmentalists who take their carbon footprint very, very seriously.

So seriously, in fact, that Vernelli aborted a pregnancy and, by age 27, had herself sterilized. Baby-making, she says, is "selfish" and "all about maintaining your genetic line at the expense of the planet."

Because Toni and her husband, Ed, are childless and vegan, they say they can justify one long-haul airplane trip per year and still remain carbon neutral.

Sarah Irving is another like-minded nature-nurturer. She and fiance Mark Hudson decided on him having a vasectomy to prevent the possibility of an inconvenient life interfering with their carbon-perfect ones.

Those of us who have managed to see a pregnancy through to birth recognize the irony of these tales.

If we're not saving the planet for our kids, for whom are we saving it? After we're all sterilized and aborted, who's going to appreciate the fact that global warming is, by golly, under control? Who's going to live to tell the tale?

Tell me: When was the last time you read a good book by a polar bear?

Human beings may unconsciously wish to maintain their genetic line, but that's not the reason most people have children. OK, most of us have children because we get pregnant. But otherwise, the planet -- glorious as it is -- is simply not that much fun with no one around.

The authors of the newspaper story seemed to have a sense of something gone awry, but I don't share their nostalgia for "innocent eyes gazing up ... with unconditional love" and "a little hand slipping into hers -- and a voice calling her Mummy."

Those little pleasures are for all to cherish in their own private moments. Please.

What I'm nostalgic for is sanity.

The couples who choose abortion and sterilization may not save the planet, but they're saving the gene pool a mess o' trouble by purging their own from the mix. The Darwin Awards folks, who honor those who improve the species by accidentally removing themselves from it, will have to create a new category:

People Too Narcissistic To Procreate.

Far be it from me to suggest that people must have children to be content or to contribute to life on Earth. But abortion should never be confused with a selfless act. It is clearly the ultimate and most-vivid expression of the opposite.

Raising children is quantifiably the most persistently unselfish act known to mankind, as millions of veterans of sleepless nights will attest. Parenthood is when "I" takes a backseat to "thou" -- when the infant-self submits to adulthood so that the real infant gets a necessary turn at the well of self-importance.

Although I doubt there are many willing to sterilize themselves in order to reduce the size of their carbon footprint, such extreme materialism is the evolutionary product of our gradual commodification of human life.

Suddenly, the unborn is of no greater importance than the contents of our recycling bin. Like Weight Watchers dieters substituting carbs for sugars, we trade off future members of the human race to neutralize insults to Earth's balance in the present.

Here's how the mental calculation goes: Let's see, if I abort my child, maybe I can travel first-class to the United Nations Climate Change Conference in Bali.

Is this the slippery slope that pro-lifers prophesied? Once such utilitarian concerns edge out our humanity -- and once human life is deemed to have no greater value than any other life form -- how long before we begin tidying up other inconveniences?

Wouldn't it be helpful to eliminate some of the less productive members of society who, like the cows they no doubt eat, are emitting hazardous methane, one of the greenhouse gases that contribute to global warming?

That seems an absurd projection, but then not long ago, so did the aborting of babies to thwart global warming. The deeply caring, meanwhile, are always the ones to watch. Tenderness, it has been said, leads to the gas chambers.

On a lighter note, we might have avoided all such concerns if only the mothers of Toni, Ed, Sarah and Mark had been as "virtuous" as they are.