There are at least three pressures to procreate. First, there’s the lure of pleasure from sex hormones that are released during sex. Humans have learned to control that pressure by separating the pleasure from procreation, with birth control techniques. Second, there’s a limited time in which reproduction is biologically feasible, so that if you’re interested in having children, you’re pressured to do so within only a certain number of years. To some extent, humans have learned to control this pressure too, by setting up infrastructures for child adoption or for raising children by the extended family. Plus, you may not be interested in having children in the first place.
Procreation and the River of DNA
But the third pressure pertains to that question of interest, although this pressure is so mind-shattering that it’s seldom consciously considered. Every animal is chemically connected to what the biologist Richard Dawkins, in his book River Out of Eden, calls a river of DNA that stretches back to the origin of life on this planet. This is to say that we’re each alive not just because of the obvious facts that our parents reproduced and that their parents did as well, but because a continuous stream of our ancestors did so, including the evolutionary ancestors of our species and the ancestors of those ancestral species, and so on back to the simplest sexually reproducing organisms. This is a biological fact rather than just a metaphor and the point isn’t merely the abstract one that humans descended from other species; rather, each one of us, and each animal currently alive, is alive only because that animal’s germ cells were produced by its parents’ sperm and egg, which themselves were produced by their germ cells, which in turn were produced by that animal’s grandparents' sperm and egg, and so on, going back countless generations and thousands and millions and billions of years. Each one of us, therefore, was literally produced indirectly by certain dinosaurs, for example, who stomped around on prehistoric Earth long enough to procreate.
The third pressure, then, is that when an animal fails to reproduce, for whatever reason, that failure is the termination of a multibillion-year-old chemical process that created millions of generations of creatures that necessarily succeeded in sexually reproducing. There’s the sense that although most of our ancestors, including our nonhuman ones, can’t know when we fail to pass their genetic material to a new generation, we nevertheless let them down when we fail in that regard, since we render their struggles ultimately inconsequential. When a person dies without reproducing and raising a child to be able to carry on the genetic legacy, the person is a dam blocking the river of DNA from flowing onward. Did the river flow for countless miles and for billions of years, through its dinosaurian and mammalian host organisms, only to be stopped by Joe Blow, who slips on a sidewalk and dies prematurely or, even worse, who chooses not to have children even when he has the resources to honour his ancestors’ victories by letting their river of DNA flow through him as well? There’s the feeling that life is precious and that if everyone ceased reproducing, ending life on this planet, the loss to the universe would be unfathomable. Thus, when even a single person takes a step towards realizing that possible lifeless future, by failing to procreate, the person sins against the sacredness of life.