“Any conjecture gets muddled by our obstinate reluctance to accept that the worst might actually occur. We may be undermined by our survival instincts, honed over eons to help us deny, defy, or ignore catastrophic portents lest they paralyze us with fright. If those instincts dupe us into waiting until it’s too late, that’s bad. If they fortify our resistance in the face of mounting omens, that’s good.”

This is Weisman’s evolutionary explanation of why it is so difficult psychologically for humans to contemplate worst-case scenarios like our own extinction. He suggests that a once-beneficial trait may have become maladaptive in the present era. For early humans, acute awareness of and sensitivity to threats could have inhibited activities like hunting, thereby reducing survival rates, whereas today, it could motivate us to make the onerous behavioral adjustments needed to put industrial civilization on a more sustainable path.

“Suppose that the worst has happened. Human extinction is a fait accompli. Not by nuclear calamity, asteroid collision, or anything ruinous enough to also wipe out most everything else […]. Nor by some grim eco-scenario in which we agonizingly fade, dragging many more species with us in the process. Instead, picture a world from which we all suddenly vanished. Tomorrow. Unlikely perhaps, but for the sake of argument, not impossible.”

Weisman articulates the thought experiment that is the book’s premise. He specifies that humanity is eliminated without collateral damage because he wants to imagine how nature would respond in its present state, not in some future state of even greater degradation resulting from our prolonged, losing battle for survival.

“The matter is more complicated than a killer instinct that never relents until another species is gone. It involves acquisitive instincts that also can’t tell when to stop, until something we never intended to harm is fatally deprived of something it needs. We don’t actually have to shoot songbirds to remove them from the sky. Take away enough of their home or sustenance, and they fall dead on their own.”

This is another evolutionary analysis of human behavior, in this case explaining why we have caused so much environmental damage throughout the history of our species. The instinctual drive to hunt and to acquire useful possessions ensured the survival and flourishing of early humans, but it became maladaptive as mushrooming population and advancing technology expanded humans’ capacity to consume resources and transform nature.