Extended lifespan and population growth

[Omnis]

Just a hypothetical question I thought I'd through out there: if it became common for human beings to live for up to, say, 250 years, with everyone being able to reproduce for most of their lifespan, what effect might this have on the growth of population? Let's assume, for example, that everyone born in the 21st century will live this long. I'm pretty sure the effect would be somewhat dramatic, but I was wondering if anyone out there would care to do a little quantification?

[Ursa major]

Before we can even start to answer that question properly, we need to know how this situation has come about. I don't mean the details of the science, but those of the society (or something outside that society) that makes such an outcome not only possible but universal. Is the whole world "rich" enough to be treated for the many symptoms and causes of ageing? Have some causes of ageing been magicked away (though not necessarily by real, working magic)?


Once we know that, perhaps we could apply what we know about changes in, say, family size in the world we know. What I'm thinking of here is the decline in family size with (apparent) wealth. People in the "richer" countries now choose to have smaller families; biologically speaking, they could still have large families, as their ancestors did, as still happens in some societies today.

Many reasons have been given for this - less infant mortality, more non-family-based care of the elderly, sources of income not based on the number of hands that can be put to the wheel, etc. - which may may not be valid. All other things being equal (only you know if they're not), the same reasons will probably apply in the situation you're asking about.

[Omnis]

I was basically thinking that extended lifespans would be possible through two generations of treatment: the first would involve "somatic" methods such as replacement of defective organs and "cellular cleansing" whereby failing cells are removed from the body so that healthy ones are able to replicate freely (for a picture of what I'm talking about, I would recommend the "Curiosity" episode "Can You Live Forever" on the Discovery Channel). While such treatments would theoretically (but not always practically) be able to extend the human lifespan indefinitely, they would eventually be superseded by a "germ-line" genetic treatment that gives each recipient (and all of their descendants thereafter) a reliably extended lifespan of about 250 years, essentially eliminating the need for "treatments" altogether (except for those adventurous souls who want to try going beyond 250 years). The first generation of treatments would probably be more common among wealthy individuals/families who can afford the expense of continuous treatment over their lifetime, while the second generation treatment would bring extended lifespans within the means of ordinary people by requiring only one treatment in one family generation.

[Interference]

People being what they are, the rise in population would be spectacular and almost impossible to moderate without intrusive government regulation. Of course, some religions will either have to back down from the "go forth and multiply" imperative or come into conflict with the law, which might be an interesting line to pursue in fiction.

Somewhere around here there's a thread about immortality and whether or not people will be more or less likely to get involved in extreme sports, among other things, to pass the time. The same questions hold, I think, for prolonged life. How bored might people become, how would the suicide rate be affected, how dangerous might life become and will it become slightly less valued?

On the other hand, some long space journeys could be made within a single generation

[Vertigo]

There are a couple of threads about immortality where population has been considered as one of the issues. I personally figure that if we discovered life extension of up to 250 years anytime in the near future, it would have to be suppressed because of the population issue or massive birth control would have to be enforced. Paolo Bacigallupi dealt with the latter situation in a truly grim little short story called Pop Squad in Pump Six and Other Stories.

However one point to bear in mind - to achieve what you have stated in the opening post - "with everyone being able to reproduce for most of their lifespan" - would require some major new genetic twists; probably far more than achieving longevity on its own. You would have to either increase the number of eggs a human female is born with, or ensure more of them survive to puberty, and then somehow induce more of the oocytes (I believe they are called) to mature into ova.

Bottom line extending lifespan is a totally different problem to extending female fertility.

However even if women didn't stay fertile for any longer than they do today you would still have a tremendous problem. Currently I suppose on average in any one family there are probably 3 to four generations alive at a time. If life expectancy went up to 250 years you are talking 9 to 12 generations alive at a time. So straight away you have trebled the population before the first of your 250 year olds die.

[Glitch]

You can probably find your answer by looking back at history.

The world's population has increased from 1 billion to 7 billion in the last 200 years.

It looks like it took about 70 thousand years for the population to increase from 1 million to 50 million. This seems due to the invention of agriculture.

Another one thousand years to increase to 400 million. Then by 1800 it had reached the 1 billion I mentioned at the start.

During the Roman Empire, Romans had a approximate life expectancy of 22 to 25 years. In 1900, the world life expectancy was approximately 30 years and in 1985 it was about 62 years, just two years short of today's life expectancy.
source - http://geography.about.com/od/popula...expectancy.htm

It looks like the world has already seen life expectancy double, which is kind of what you are asking ?

[hopewrites]

Vertigo, women are born with enough ova to hold that fertility up, its menopause that cuts us short. So if we assume that the slowed aging that allows humanity to extent it's life expectancy also slows the onset of menopause then there is no problem with the fertility of the proposition.

I think the biggest mitigation on family size would be cultural, and whether or not the governments provided help to families that could not provide fully for themselves. I would assume that retirement would move back to 225-245, which would increase the incentive to finish lots of schooling before entering the work force. With multiple generations able to work we might be able to convince people/governments that "minimum wage" doesnt need to be a "living wage" and thereby help bring back "entry level employment" positions.
Social and biological pressures to 'start a family' would decrease on young people and you will likely see the average age of parents (especially new parents) rise. which would help to spread out the generations alive at one time to between three and five.
We could add an age classification that we give other species but not to ourselves; "sub-adult" covering persons aged 16-52(age range based on the equation [X to X+2X] where X=the time it takes for a creature to reach what appears to be physical maturity), where it is acknowledged that one is physically mature, but not yet emotionally/ mentally mature.

I would like to think that people would slow down and take more time to enjoy life while living it, but feel it is more likely that we would keep rushing on at an exponentially exhausting pace.

[Vertigo]

Hopewrites I am certainly no expert on the subject however this is what I found, though I certainly can't vouch for it's correctness:

A baby girl is born with egg cells (oocytes) in her ovaries. Between 16 and 20 weeks of pregnancy, the ovaries of a female fetus contain 6 to 7 million oocytes. Most of the oocytes gradually waste away, leaving about 1 to 2 million present at birth. None develop after birth. At puberty, only about 300,000—more than enough for a lifetime of fertility—remain. Only a small percentage of oocytes mature into eggs. The many thousands of oocytes that do not mature degenerate. Degeneration progresses more rapidly in the 10 to 15 years before menopause. All are gone by menopause.

The real question then is whether slowing down the aging process will also slow down the degeneration of the oocytes. If it does you are correct but I'm not so sure this is actually an "aging" process but I may be wrong. Certainly the first form of life extension mentioned - replacing of organs - would not fix this problem (incidentally one aging organ that would be very hard to replace would be our skin).

However the bottom line is, I am certain, that without controls there would be a very significant increase in population. Considering it is estimated (I believe) that, living as we do in Europe, the sustainable maximum population that the planet can support is reckoned to be around 3.5 billion (more like 2 billion if everyone lived as they do in America), and our current population is 7 billion I think the situation would rapidly become catastrophic.

[David Evil Overlord]

I was about to post, and then my post became a short story idea. So I'm keeping it. So there.

[mosaix]

The question remains whether people would want to continue reproducing. I know there are many examples of extremely large families but the average number of children per family is 2.4

In western society, at least once, it would appear that parents have two or three children then choose not to have any more. That's a social thing, not a question of fertility.

I'm 65 and, along with my wife, brought two children to adulthood. Although I love them both dearly, it's not an experience that I would choose to repeat - no matter how long I lived.

[Interference]

I think some people will continue to enjoy highly active lives. Whether any new lives that result from these activities are within wedlock or not is an entirely other matter.

Even today, it isn't only "celebrities" who brag about the number (in some cases in the thousands) of "conquests" they've made. A guy I knew at college needed to be tied down at parties

[mosaix]

Originally Posted by Interference

I think some people will continue to enjoy highly active lives. Whether any new lives that result from these activities are within wedlock or not is an entirely other matter.

Even today, it isn't only "celebrities" who brag about the number (in some cases in the thousands) of "conquests" they've made. A guy I knew at college needed to be tied down at parties

I agree with what you say Interference. But the activity you describe doesn't necessarily have to result in offspring.

[Ursa major]

"'Til Death Do Us Part": a whole new ball game.

[Interference]

That would be a sport I'd watch

Originally Posted by mosaix

I agree with what you say Interference. But the activity you describe doesn't necessarily have to result in offspring.

True, so true, so why then is our population currently standing (sometimes sitting, often lying) at 7 billion + while the number of marriages is declining, re-marriages rising and divorces, separations and undefined independents are going through the roof?

I'll tell you why:

The population is full of gosh-darned people, that's why!


And the roof is leaking.

[mosaix]

Originally Posted by Interference

That would be a sport I'd watch



True, so true, so why then is our population currently standing (sometimes sitting, often lying) at 7 billion + while the number of marriages is declining, re-marriages rising and divorces, separations and undefined independents are going through the roof?

I'll tell you why:

The population is full of gosh-darned people, that's why!


And the roof is leaking.

I read somewhere, can't find it now, that the population of Japan is projected to fall by half by the end of the century.