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What none of these predictions address, however, is the impact those extra years, decades or centuries may have on our wellbeing — and on what it means to be human.

The oldest person on record is Frenchwoman Jeanne Calment, who died at the age of 122 in 1977. She married well and never had to work. She was still riding a bike at 100 and smoked until the age of 117. She also survived a husband (food poisoning), her only daughter (pneumonia) and her lone grandson (car accident).

As some ethicists have started to ask, how much life is too much?

The answer to that question is deeply personal, of course. But it is political as well — because the average life expectancy in the United States has already doubled over the past 200 years, to 78.7, while in other parts of the world it has stalled at 52.

Those pushing for extreme longevity are also the ultimate “haves,” white, male tech billionaires: The founders of Google and Facebook have put huge money behind anti-aging research; SENS is backed by PayPal’s Peter Thiel and German internet entrepreneur Michael Greve.

“I doubt there are many people in Ethiopia or Bangladesh who are clapping their hands at the idea that some rich guy in Silicon Valley is trying to live another 100 years if their kids are dying from malnutrition or some easily handled health problem,” says bioethicist Arthur Caplan.

And if only the ultra-rich can afford longevity therapies, could their success lead to a new underclass of the un-enhanced, “parallel populations,” as University of Manchester philosopher John Harris has described it, “of mortals and immortals existing alongside one another”?