Time magazine cover story on women who choose not to have children (“The Childfree Life: When having it all means not having children“) is igniting a national debate that is both highly personal and highly important to the future of the world.

My wife and I chose to be “childfree” long before the term was invented. We decided that having a child was not for us. It was not a terribly difficult decision. We like children, but we did not like them enough to take on the commitment of raising them. We knew there was a chance that we might later regret that decision, but so far at least there has been no regret.

Some may characterize our decision as selfish, and in a sense it was, but I suspect that the decision about whether to have children or not is inherently a “selfish” decision. Couples who really like children and who look forward to the joys and personal fulfillment that can come with having them are also acting out of “selfish” instincts. They are acting on their personal preferences. They are doing what they want.

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Some, however, would argue that not having children is somehow more selfish than having children. Some, like Satoshi Kanazawa, a psychologist at the London School of Economics, assert that it is not just selfish, it is unnatural:

If any value is deeply evolutionarily familiar, it is reproductive success. If any value is truly unnatural, if there is one thing that humans (and all other species in nature) are decisively not designed for, it is voluntary childlessness. All living organisms in nature, including humans, are evolutionarily designed to reproduce. Reproductive success is the ultimate end of all biological existence.

Unnatural? Really? The fact that most people have a biological urge to reproduce does not make it unnatural for some people to lack that biological urge. From a biological standpoint, it may be important for a species to have enough offspring to ensure that the species survives and enjoys “reproductive success.” But with 7.2 billion people [PDF] on the planet and demographers telling us that we will likely add another 2.4 billion people over the next 37 years, humanity is hardly in any danger of shuffling off its mortal coil.

If Kanazawa and others believe that “reproductive success” requires that we all have children, then we need to have a healthy public debate about what constitutes “reproductive success.”

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I would argue that “reproductive success” for the human race is not having more offspring than the Earth can reliably sustain. And if that is a fair measure of reproductive success, the evidence strongly suggests that we should be having fewer children, not more.

By some estimates, humanity is already using about 150 percent of the Earth’s renewable resources, and by 2030 we may need two planets to sustain us for the long term. We are, in other words, in mortal danger of over-utilizing the planetary resources that our children and their children will need to survive.

Just take a look at the mark that we are leaving upon the world. In many regions, major rivers are being reduced to a trickle by the time they reach the sea. Lakes are shrinking and water tables are falling at a precipitous rate. Tropical forests are being hacked down to satisfy our demand for hardwoods and palm oil. Ocean fisheries are collapsing as a result of overfishing. We are rapidly exhausting our limited inheritance of metal and minerals. Vital bio-habitats, including coral reefs and wetlands, are disappearing at a fearsome rate. Scientists warn that human activity is triggering the “sixth mass extinction” in the history of the world. Within the lifetimes of children being born today, humanity will likely preside over the virtual extinction in the wild of lions, tigers, elephants, and rhinos. And then there’s the question of what we humans are doing to alter the planet’s climate and the impact that will have on the future of all life, including human existence. That’s not my idea of reproductive success.

I do not deny couples the right to have children, nor do I disparage their decision to have children. I would certainly never argue that having children is unnatural. But, conversely, no one in today’s overheated, overpopulated world should ever characterize the decision to be “childfree” as unwise or unnatural.

Reproductive success, however we measure it today, should ensure that future generations inherit a better world, not a more populous one.

See also: Time magazine catches on to the childfree movement, misses the green angle