Would it be good if the average human life-span were not 75 to 80, but 150? 500? 1000? Peter Singer raises the question in
this online editorial. To get the ball rolling, let's ponder three mini-worlds. The first world is more or less like ours, while the second and third involve longer life-spans. In "30-90" people on average have a child at 30 and die at 90 (couples have two children). So, starting with two people, A and B, here's how things look over time--
30-90 WORLD
year people
0 A B
30 A B C D (A and B have C and D)
60 A B C D E F (C and D have E and F)
90
A B C D E F G H (E and F have G and H; A and B die)
120
A B C D E F G H I J (etc)
150
A B C D E F G H I J K L
180
A B C D E F G H I J K L M N
210
A B C D E F G H I J K L M N O P
240
A B C D E F G H I J K L M N O P Q R
Population density stabilizes at: 6
Total people who exist in 240 years: 18
Now picture a world with longer average lifespans--say, 150 years--but the same average age of reproduction.
30-150 WORLD
year people
0 A B
30 A B C D
60 A B C D E F
90 A B C D E F G H
120 A B C D E F G H I J
150
A B C D E F G H I J K L
180
A B C D E F G H I J K L M N
210
A B C D E F G H I J K L M N O P
240
A B C D E F G H I J K L M N O P Q R
Population density stabilizes at: 10
Total people who exist in 240 years: 18
In 30-90, people are replaced by their great-grandchildren. In 30-150, by contrast, they're replaced by their great-great-great-grandchildren. You can picture this vividly by imagining someone on their deathbed. In 30-90, at most there will be two generations of descendants on hand. In 30-150 there could be 5 generations of descendants.
30-150 is an environmentally problematic departure from our world. The increased population density means greater strain on resources. We get something--longer life--but at a high cost. For this reason (I imagine) Singer adds delayed child-bearing to the picture. Now suppose people give birth at 90 and die at 150 (these mini-worlds are my invention, not his)--
90-150 WORLD
year people
0 A B
30 A B
60 A B
90 A B C D
120 A B C D E F
150
A B C D E F G H
180
A B C D E F G H I J
210
A B C D E F G H I J K L
240
A B C D E F G H I J K L M N
Population density stabilizes at: 6
Total people who exist in 240 years: 14
90-150 is no more environmentally burdensome than 30-90, since population density stabilizes at the same level. But fewer people exist in 240 years--4 fewer than in the other two worlds.
1/22 Thanks to a commenter I see I've made a mistake here. I've got only the first generation reproducing at age 90. Will fix when I have a moment....
1/23 Upon further reflection--to maintain the same population density, we just need to maintain the same ratios. People need to reproduce 1/3 of the way into their lives, as in 30-90. So we need to look at a 50-150 world. (If people lived to 900, they'd have to reproduce at 300, etc. etc.)
50-150 WORLD
year people
0 A B
50 A B C D
100 A B C D E F
150 A B C D E F G H
200 A B C D E F G H I J
240 no change
Population density stabilizes at: 6
Total people who exist in 240 years: 10
Will make changes below so that I'm comparing 30-90 to 50-150.
So which is the best world? Singer seems to be open to the possibility that 50-150 could be best. There are fewer deaths from old age per unit time. People spend less time fearing death, since the end of life is further in the future. One downside he mentions is "the missing people"--O, P, Q, and R in my mini-model. They exist in both 30-90 and 30-150, but not in 50-150. We shouldn't be concerned about them, Singer seems to say--
One reason for thinking it better to have fewer people living longer
lives is that only those who are born know what death deprives them of;
those who do not exist cannot know what they are missing.
I'll buy that we haven't mistreated O, P, Q, and R by not creating them. We haven't done them any personal harm, since they aren't around to harm. But that's not the worry I would have about the 50-150 world. My worry is about the people in 50-150, not the people left out.
But first, a word about delayed reproduction. Singer and other life-extension advocates seem to think delayed reproduction might be in the cards. He writes--
contrary to what most people assume, success in overcoming aging could itself give us breathing space to find solutions to the population problem, because it would also delay or eliminate menopause, enabling women to have their first children much later than they can now.
I don't really understand this. In what sense would people in 50-150 be better positioned than people in 30-90 to solve the population problem? (Indeed, what population problem? Population density is no greater in 50-150 than in 30-90.) In any event, my understanding is that menopause is not a product of aging. A fascinating
article Jared Diamond published a couple of years ago says menopause is actually adaptive. Women go through menopause because it helps them have more descendants if they function as grandmothers instead of adding to their existing offspring. So anti-aging research isn't going to eliminate or delay menopause. Only anti-menopause research is going to eliminate or delay menopause.
But OK, suppose we undertake both. So we are biologically able to shift from 30-90 to 50-150. Would we really want to? I have three misgivings--
(1) Delaying child-bearing until 50 sounds about like putting off sex until age 50, or romance, or reading novels, or drinking coffee. The good stuff in life shouldn't get postponed 50 years! I don't see the proposed trade here (early reproduction for delayed death) as a terribly attractive one.
(2) I think life extension advocates are mistaken about the psychology of death in old age. They see 50-150 as preferable because, though there's just as much living going on in 50-150 (there are just as many person-hours) as in 30-90, there are fewer deaths in 50-150, and fewer hours of apprehending death. But how do people feel as they approach death? Surprisingly unbad. It's intriguing that positive psychology shows, quite consistently, and all around the world, that happiness over time fits a U-shaped curve. We are happier as we leave middle age and get closer to the end of life. My experience spending time with very old people is that they're remarkably cheerful. They are masters of black humor, and don't worry over much about impending death. So 50-150 solves a problem that may not really exist to begin with.
(3) My most serious worry is about the lower total population of 50-150. 10 people wind up existing in 240 years, in contrast with 18 in 30-90. The reason this troubles me is not because I'm concerned about the four missing people. They are not harmed by not coming into existence. The reason why 30-90 seems better is because it has greater human richness. It's more diverse because eight more people come into the world, and that diversity has advantages for the people who exist in that world. Greater human diversity goes along with more intellectual and technological progress, or so it's been hypothesized by authors as diverse as Matt Ridley (
the Rational Optimist), Toby Ord (see this
short post, watch
this video, and Cass Sunstein (
Infotopia: How Many Minds Produce Knowledge). They hypothesize that the huge current population of the world is one reason why we are at a point of unprecedented development in many areas. More people means more specialization, more minds working on problems. The crucial thing here is not just how many people exist
at a time, but how many exist
over time. Arguably, 30-90 is better than 50-150 for the reason that more people are around to contribute to the human enterprise in 30-90 (though the same number exist at one moment in time).
Now, the progress we get from large populations comes at an environmental cost. So nobody's saying "the more the merrier (period)". But the extra diversity of 30-90, compared to 50-150, has no environmental cost at all. The population density of the two worlds, at any moment in time, is identical. So by transitioning to 50-150 we'd be giving up human diversity (with probably loss of progress), and gaining nothing, environmentally speaking.
People do fear death and want more years of life, of course, so there's something attractive to most of us in the idea of anti-aging research. The talk of human diversity and progress doesn't have any power to help us face death. It's all abstraction and speculation, no consolation. Or is it? I actually do find some consolation in the notion that new people make the world a better place. It would not have been for the best if our ancestors in 1500 had discovered a longevity pill, allowing them to live for 1000 years. The cast of characters on the human stage would have been much reduced and that would have been for the worse. I think we
can take comfort in the idea of a new cast of characters coming into existence, especially if we live in such a way that we identify strongly with future people. That way we will one day be out with the old, but we'll also (in various attenuated senses) still be in with the new (see Mark Johnston's interesting book
Surviving Death for thoughts along those lines). I think 30-90 is OK, if not perfect, and possibly quite a bit better than 50-150.