It is probably wise to take Thiel’s idea of an end to aging (or at least its radical postponement) seriously. Any extrapolation from technological progress over the past quarter-century makes the notion plausible. At least seriously enough to ask the question: Do we want this Shangri-La? Do we want a world of boomerang generations where, like Prince Charles still awaiting his big job, we’ll be lucky to come into an inheritance at 80?

More seriously, given limited natural resources, already aging populations, spreading megacities, a dearth of jobs in the developed world, severe strains on health services, disappearing pensions and growing inequality, the idea of radically extending life (initially for the rich, one assumes) seems ominous — even if human adaptability and ingenuity are always underestimated.

Then there are the deeper moral issues. Nature can, of course, be improved upon or we would still be dying of polio. But it would be rash to imagine that tampering to this degree with our human lot and altering so radically the delicate equilibrium of humankind and nature will not produce plenty of Donald Rumsfeld’s “unknown unknowns,” deathless monsters of our own creation. Radical life extension smacks of an intemperate claim to have unlocked the fundamental mystery of life. That is dangerous territory.