Animal suffering is inevitable even without humans---but staying alive allows evolution that’ll produce compassion and prevent it

To conclude this section, we ask a supremely important question: how should we respond to the risk of a catastrophe that would bring about the extinction of our species? If, with Sidgwick, we agree that ‘life on the average yields a positive balance of pleasure over pain’—or if we are not hedonists, but agree that on average it has more positive than negative value of some other kind—we are likely to think that human extinction would be a very bad thing. One reason for not drawing this conclusion would be that the suffering humans cause, and will continue to cause, animals outweighs the value of human existence. But animals also suffer greatly when they live naturally, without human interference, and if humans become extinct, there is no hope of that situation changing, whereas the continued existence of human beings does offer the hope that eventually we will be both intelligent enough and compassionate enough to reduce that suffering.

How bad, though, would human extinction be? That question is not merely theoretical, because there are things that we can do to reduce the risk of human extinction. There is, for example, a small chance that our planet will be hit by an asteroid large enough to wipe us out. We are already tracking such objects in space and seeing if they pose a risk to us. It is probably within our capabilities, if we were willing to devote enough resources to it, to build a rocket that would intercept any asteroid that is on a collision course with us and deflect it from that course. If the chances of a doomsday asteroid hitting Earth during the next century are around one in a million, how much should we be prepared to spend on such a project?52 To reach a sound answer to that question we would need answers to many relevant factual questions, including whether we could spend the resources better combating other risks of extinction (nuclear war, a pandemic, global warming speeding up to the point at which it makes our planet uninhabitable, and so on). But the philosophical issue we have been discussing is also relevant. Parfit shows this by asking his readers to imagine three possible scenarios for the future of our planet:

(1) Peace.

(2) A nuclear war that kills 99 per cent of the world’s existing population.

(3) A nuclear war that kills 100 per cent.

Any sane person will agree that (2) would be worse than (1) and (3) would be worse than (2). But which is the greater of those differences? Parfit’s judgment is that the difference between (3) and (2) is ‘very much greater’ and he justifies this by pointing out that the Earth will remain habitable for at least a billion years, and if we do not destroy ourselves, the entire history of civilization will be just a tiny fraction of human existence.53

Those who accept the prior existence view will not share Parfit’s judgment. They will focus on the loss of life of those who exist now, or will exist in future, irrespective of what we do. On the prior existence view, the difference between (3) and (2) is relatively small, whereas the difference between (2) and (1) is very large. Parfit’s answer presupposes that there is some value in the existence of beings who would not otherwise exist, as long as they live good lives. Because there are so many people who will exist, if our species survives for a billion years, Parfit would not have to hold that their lives have the same value as the lives of presently existing people, but he must hold that they have some value.

We can now return to the question of how much we should be prepared to spend to prevent threats of extinction. The debate over the value of bringing into existence beings who will have good lives, but whose existence is contingent on our making certain choices, is lively, complicated, and raises deep philosophical questions. The widespread belief that couples are under no obligation to have children, even when those children will have good lives, provides some intuitive support for denying that there is value in bringing new beings into existence. This position also has the merit of avoiding the repugnant conclusion. On the other hand it makes sense to hold—as Sidgwick seems to have held—that in contemplating bringing them into existence, we should give the lives they will lead as much value as the equally pleasant lives of anyone else. No one, on the other hand, thinks that the lives of future possible beings should count for more than the similarly good lives of presently existing beings. This situation again seems one in which we ought to compromise, and in our practice, give some positive value to the lives of future beings. Even if we think the prior existence view is more plausible than the total view, we should recognize that we could be mistaken about this and therefore give some value to the life of a possible future—let’s say, for example, 10 per cent of the value we give to the similar life of a presently existing being. The number of human beings who will come into existence only if we can avoid extinction is so huge that even with that relatively low value, reducing the risk of human extinction will often be a highly cost-effective strategy for maximizing utility, as long as we have some understanding of what will reduce that risk.54