November 05, 2006
Eternal Youth, Overpopulation, And Instincts To Reproduce

World overpopulation is one of the biggest problems posed by the eventual development of biotechnologies that can reverse aging. People who now die from old age will stay around. Since their entire bodies will be rejuvenated they'll also regain or maintain the ability to reproduce. The death rate will drop to a level caused by accidents, murder, and suicides. At the same time, more people will have babies and they'll be able to have babies for hundreds and perhaps even thousands of years.

What to do about it? I have one thought: Genetically engineer offspring to remove instincts for reproduction. Surely instinctive desires for children exist in our DNA and they'll be discovered within the next couple of decades as DNA testing technologies become cheap and easy. So in theory it should be possible to make sure that at least new generations will not desire to have kids.

The people who are born to lack the instincts to reproduce won't miss these desires. Imagine you lacked the desire to eat some kind of food and found the taste of it disgusting. Would you miss it? I know even women who are totally turned off by the idea of having kids. They do not miss that desire at all.

The vast majority of people who are already alive when we develop rejuvenation technologies pose a much bigger problem. Faced with centuries of life and driven by instincts that make them like babies and children they'll want to have kids. Some will want to have more kids after their own have long grown up and moved away. Many want grandchildren and so will oppose genetic engineering of offspring to remove the reproduction instincts. So it is not clear that my proposal here has a chance. But I figure it is worth some discussion.

One final point: Genetically engineering people to lack the reproduction instinct? Are you mad? Well, I'm already imagining a world where most people (at least in industrialized countries) do not grow old. People will use drugs to enhance their intelligence and control their emotions. They'll genetically engineer their offspring to look and think more to the liking of the parents. These are all things most will embrace voluntarily as soon as it becomes possible to do so. But we are driven by instincts as much as by reason and some of our instincts have become quite problematic for the health of society. In the interest of freedom should we allow people to act on their instincts and drive the human population up into the tens of billions? Sounds like a bad future to me. We should find some way to avoid it.

Update: To the people who argue that fertility rates have already fallen in many countries and who expect that trend to continue I say you underestimate the power of natural selection. The fall in fertility rates is exerting a strong selective pressure for genetic variations that increase fertility. Those people who are having babies are passing along more alleles that favor reproduction in industrial societies than existed in previous generations. New generations of the human race are getting selected to have greater desire to have kids. Whatever genetic qualities which increase desire to have kids are getting selected for. What desires and attributes which distract from having kids are getting selected against.

The human race has to defeat Darwinian natural selection if it is to prevent runaway population growth. The only way to defeat selective pressures for reproduction in an eternally youthful society is to genetically reengineer humanity to reduce reproductive urges. Selective pressures for reproduction could be delayed and reduced in a society ruled by a totalitarian government that forbade reproduction. But such a government would not be stable because a very sizable fraction of the population would feel frustration and anger over restrictions on reproduction and would seek to overthrow the government.

Share |      Randall Parker, 2006 November 05 04:37 PM  Bioethics Rejuvenation

Mike Anderson said at November 5, 2006 7:38 PM:

Don't solve a problem that doesn't exist. Nearly all the countries that have the wealth, technology, and desire to extend lifespan indefinitely also have sub-replacement birth rates. If this sort of Demographic Transformation continues to spread, the civilized world may need life extension just to make sure we don't go extinct. High birth rates will be for people who seek Paradise in the next world, life extension will be for those who seek it in this one. Some of us will find it in both.

Christopher Rasch said at November 5, 2006 7:51 PM:

Fertility rates are below replacement in half the world already, including all of Western Europe and Japan. The U.S. is slightly below replacement levels. Increasing lifespan and wealth do not seem correlated with increased population -- if anything, the reverse appears to be true.

In the interest of freedom should we allow people to act on their instincts and drive the human population up into the tens of billions? Sounds like a bad future to me.

Of course, no one wants to live in a Soylent Green future. However, past government attempts to limit population growth have resulted in problems of their own.

Those who wish to have large families are limited by the costs of providing for their children. If the population begins to outpace the carrying capacity, then vital necessities (such as food, housing, medicine) will become more expensive, which will, in turn, cause families to restrict the number of children they have.

What's the trend to date? Historically, in most of the world, the cost of food has declined over the past 50 years, even as the world population has doubled.

Food prices, whether at the store or at a restaurant, have been declining relative to prices of all other items. Between 1952 and 2003, the ratio of food prices to the price of all other goods has fallen by 12 percent. But the drop is more dramatic if we factor in "quality" improvements—the reduced time cost of acquiring and preparing food (convenience), greater variety, and omnipresent restaurants and vending machines. Foods that once were available only seasonally are now available year-round. Advances in food processing and packaging have introduced a multitude of ready-to-eat foods, available virtually anywhere and at any time.


Currently, both population levels and resource costs in advanced nations are in long term declines. I don't think there's much need to worry about the effects of immortality on population growth until those trends reverse.

Jake said at November 5, 2006 7:51 PM:

I heard a speech by a population expert who said that greatly extended life spans would not increase population.

People would have a decreased desire to reproduce as they would feel a lessened need to replace themselves.

Ivan said at November 5, 2006 8:26 PM:

What about space?

Semi-efficient solar power + a space elevator + resources from our solar system = more than enough resources for a trillion people.

That's a guess, obviously, but you only need to compare the volume of the earth to the livable surface area to glean that there is great potential for growth.

Also, the "ultimate resource" is human intelligence. A trillion humans will mean the number of PhDs working on the hard problems mentioned above to alleviate troubles will be quite large.

Talk of genetically engineering a certain motivation is pretty premature, given we don't quite know what people will do with their extra decades/centuries, let alone what they'll do about their kid's brains.

Space solves almost all problems, because almost all problems stem from resource and energy limitations which go away when you can mine even our own system.

Jeff said at November 5, 2006 9:25 PM:

My grandparents on my Mom's side each had over 8 siblings (think my grandfather was one of 13 kids). They lived and worked on a farm, of sorts. When their environment changed (they moved to suburbs and got industrial work), they decided to only have two kids. Note I said "decided". In turn, each of their kids (my Mom and my aunt), had 3 and 2 kids respectively - decisions, not fate or instinct. I have two kids who, since my wife and I had to use fertility treatments, were most definitely results of decisions, not instinct.

So, don't discount how a new environment will change the way humans think and behave. I'd be more worried about the poor masses who are having 9 kids because they still live in a pre-industrialized reality and cannot afford longevity treatments, but they know the wealthy are living healthy lives past 200. They may rise up and solve your overpopulation problem for you with picks and shovels purely out of spite...

Joseph Hertzlinger said at November 5, 2006 9:35 PM:

If there is a limit to the number of people on Earth, we can expect rents to rise. Higher rents usually go along with declining birth rates.

If we look beyond Earth to the rest of the universe, we can expect lots of people to travel close to the speed of light looking for cheaper neighborhoods. In that case, time dilation can slow population growth.

Randall Parker said at November 5, 2006 9:47 PM:

Christopher Rasch,

But what about the other half of the world? In Niger and a few other countries the decline in the fertility rate has stopped and reversed.

The countries with lower fertility rates are becoming a smaller percentage of the entire world population. Total fertility in the next generation will not be an average of the lower and higher fertility nations. Rather, the higher fertility rate nations will become a larger percentage of the average.

In the lower fertility rate nations something else is going on. When the average fertility is, say, 1 child per woman that does not mean that each woman is having one child. Some are having none. Some are having 2. Some are having 3 or 4. Those who are having more will be genetically much more highly represented in the next generation than they were in the last generation.

There's a genetic average difference between those who have more kids and those who have fewer. We will eventually see fertility rebounds in all the nations that are hitting very lower fertility rates. Darwin wins. There's no escaping the power of natural selection with mere industrialisation of societies.


The desire to replace oneself is not the main motivation to reproduce.

Randall Parker said at November 5, 2006 10:04 PM:

Joseph Hertzlinger,

If a high cost of living (as compared to level of income) were a reason by itself to have fewer children then we'd see much lower fertility rates in the poorer countries.

As long as humans are living well above the level needed to get enough calories to survive selective pressures will result in increases the frequencies of alleles that cause a rise in fertility.

The human brain is a product of natural selection and natural selection is still working on it. The aspects of modern industrial societies that cause some people to have fewer than 2 children do not work equally on all. Some will have lots of kids no matter what occupation they have or circumstances they live in. Their genes which increase their instinctive desire to reproduce will be much more widely represented in later generations.

There are 14 countries with fertility rates higher than 6. Their people are going to become an increasing portion of the total world population. They are poor. That is not stopping them from having lots of children.

Fertility rates will not continue to fall. They'll bounce back as natural selection works its effect.

PacRim Jim said at November 5, 2006 11:15 PM:

The reason most of us reproduce is to perpetuate ourselves--more specifically, our genes. A practical immortality, it has been called. If immortality of a sort becomes possible, will we need children? We will become our own children.

spiny widgmo said at November 5, 2006 11:53 PM:

I think people in advanced societies have their reproduction rates drop due to opportunity cost. In North America, the opportunity cost for middle class child number is approximately 300K over 22 years, with the bulk of the payment on the last few years. That is a lot of opportunity cost. It can mean the difference between an enjoyable retirement and none. It can mean the difference in vacations, career and discretionary time. In an advanced society, children are a net economic loss to the parents.

I suspect that culture, economic circumstances, and religion are larger influences than genes over just a few generations. In the advanced countries, opportunity cost plus these influences and a little bit of instinct drive the decisions to have children.

Regarding life extension and overpopulation, I suspect that even the combination of factors that influence higher fertility will damp out with many relatives living rather than dieing out. There will be less parental encouragement for their children to have kids. A counter to this is that in cultures that have mult-generation households, the children may again become household contributors rather than net wealth drains because the working career is extended.

Some questions? If life extension significantly increases lifespan and health, how will family relations change? What does it mean to have your life overlap your children and parents by score of decades? Will families become closer or more distance? What cultural influences will come into play? How will life extension affect marriage?

How will life extension affect finances? I can see wildly different outcomes in a 200 year life between the debt maximizer and the mild saver? Will this lead to more envy or less because anyone who can not use compounding over 200 years obviously has no financial discipline?

DRJ said at November 6, 2006 12:16 AM:

Are you assuming that other factors won't affect the rates of births and deaths? With longer lifespans, a percentage of the population may pursue more adventurous leisure/risktaking activities so accidental death rates may increase, perhaps significantly. In addition, why would longer lifespans necessarily lead to more procreation? Isn't it just as likely, given the trends of the past 30-50 years, that a substantial number of people will devote their extra time to second careers and leisure activities? Most people realize that living longer requires more money over a longer period of time, and they also know that raising several children from one or more marriages only increases the need for money and long-term careers. In other words, for every urge to procreate there may be countervailing pressures. There is also an increased availability and reliance on a wide range of male/female birth control methods.

aa2 said at November 6, 2006 12:32 AM:

Randall you are right about the faster breeding people pushing up the average over time. However this also means the earth's population will grow exponentially even without life extension. Niger and those savage nations are growing exponentially with very low lifespans.

We are going to have to deal with these third world nations reproducing exponentially soon with or without life extension. My solution is a long term plan to non-violently remove most of the third world people from earth. And the best way to do that is to stop most of them from ever being born in the first place. Pay third world women 5,000 US dollars to have their tubes tied. Don't provide food, antibiotics or anything, unless the woman gets her tubes tied. Get them down to 1 child per woman. Then in 200 years 1 billion people becomes less then 10 million. Done across the third world that means 4.5 billion people becomes under 50 million. Keep doing it for centuries and they go almost to zero.

This still won't ultimatily solve the problem, but it buys us a great deal of time. And as I mentioned earlier it is something that will have to be dealt with in the next 100 years either way. And with more time other technologies like uploading or interstellar travel may come along that solve the problem longterm.

rsilvetz said at November 6, 2006 1:40 AM:

Overpopulation... Probably not because of some rebound of human fertility. The 10,000 year recap below suggests whatever is going on it is not a short term trend. This trend is pronounced and continuous over the last 2000 years. Something, I don't pretend to know what tho I have suspicions, is over-riding reversion to the mean. A back-of-envelope calculation suggests that absence of reversion to the mean against a 100-generation backdrop has about 1-in-10^30th power odds. This is not an accident and most likely not the consequence of fertility alleles reshuffling. Even if it's only 50 gens, it's still a 1-in-bignum call.

Nonetheless, if we achieve biologic immortality any finite birth rate in the face of attrition deaths means an ever-expanding population. If they are all value-producers/value-creators the problem is self-resolving. We will harness as much mass/energy we need to service ourselves. Malthus applies only in the extreme limit. There may be an inflection point, where for a while we may have to curtail births until the technology advancement curve accelerates far past our limited birth rate.

So the answer to Randall's question is yes, humans most likely can follow their instincts without us getting into severe trouble. Of course, I'm assuming rational populations, constitutional republics and free-markets. Otherwise the technology will not be there to get us where we need to go nor to maintain expanding standards of living.

Year - Population - Births per 1,000 - Births Between Benchmarks

8000 B.C. - 5,000,000 -80 -1,137,789,769
1 A.D. - 300,000,000 -80 -46,025,332,354
1200 - 450,000,000 -60 -26,591,343,000
1650 - 500,000,000 -60 -12,782,002,453
1750 - 795,000,000 -50 -3,171,931,513
1850 - 1,265,000,000 -40 -4,046,240,009
1900 - 1,656,000,000 -40 -2,900,237,856
1950 - 2,516,000,000 -31-38 -3,390,198,215
1995 - 5,760,000,000 -31 -5,427,305,000
2002 - 6,215,000,000 -23 -983,987,500

Historical trivia, the United States is now a sovreignity the size of the Roman Empire at its apex.

Julian Morrison said at November 6, 2006 2:13 AM:

Remove instincts for reproduction? You'll be fighting every ancestor since prokaryotes. Not to mention, anyone who refused would quickly outbreed you.

speaker-to-animals said at November 6, 2006 6:33 AM:

Better idea than trying to eradicate one of the three pillars of evolution (reproduction, survival, death).
Birthright Lotteries.

Christopher Rasch said at November 6, 2006 6:48 AM:


Most of the other half of the world are still relatively primitive agricultural societies. As they catch up technologically and culturally with the West, I expect that their birthrates will decline as well.

Bill White said at November 6, 2006 6:50 AM:

Reply to quote: Remove instincts for reproduction? You'll be fighting every ancestor since prokaryotes. Not to mention, anyone who refused would quickly outbreed you.

As for space, if there is room and resources for a trilliom people in the solar system (and that might be conservative) then whichever subset of humanity gets out there fustest wid da' mostest (to quote that Confederate cavalry general) will be in good position to assure that its memes come to predominate all of humanity. Genes are not the only selfish replicators.

Any society/culture that declines to participate in settling space -- meaning bearing children "out there" -- will see the other human cultures outbreed them. Perhaps not in years or even decades but over centuries.

Russ said at November 6, 2006 6:54 AM:

"Overpopulation" is a word in search of a context.
"Insufficient Resources" is a phrase that actually concerns me.

Bob Badour said at November 6, 2006 7:09 AM:
If the population begins to outpace the carrying capacity, then vital necessities (such as food, housing, medicine) will become more expensive, which will, in turn, cause families to restrict the number of children they have.

Christopher Rasch, I don't see much evidence for your hypothesis. People in the West have limited reproduction at the same time the carrying capacity has increased greatly. People in places like Zimbabwe have done the exact opposite.

I suspect (up until now) status hierarchies motivate reproductive decisions far more than carrying capacity. Achieving status in the West means spending a lot more time and money on each child and by spending large sums on goods unrelated to reproduction. I suspect one achieves status in some parts of the world by having more children. "Oh, he must be a very successful man. Look how many children he can support."

People would have a decreased desire to reproduce as they would feel a lessened need to replace themselves.

Jake, genes do not have desires. Ultimately, genes determine reproductive fitness, and reproductive fitness determines total fertility. In fact, reproductive fitness and total fertility are different names or perspectives for the same measure.

In other words, people do not reproduce because they feel a need to replace themselves. People reproduce because their ancestors passed along the genes that drive reproduction.

In turn, each of their kids (my Mom and my aunt), had 3 and 2 kids respectively - decisions, not fate or instinct.

Jeff, I do not think you have excluded instinct as a driver. For example, when having large families establishes higher status, the instinct to seek higher status will improve reproductive fitness, and natural selection will select for that instinct. If human agricultural society for the past 5000 years up to and including your great-grandparents' generation equated status with large families, then that environment would select strongly for the desire to seek status.

If your grandparents moved to an environment where spending more resources on smaller families establishes status, then that instinct will reduce reproductive fitness, and natural selection will select against that instinct while selecting for different instincts.

In the new environment, natural selection will increase the frequency of genes that cause people to have lots of children regardless of status. This will naturally increase the prevalence of low-status couples who reproduce without regard for the cost involved.

don't discount how a new environment will change the way humans think and behave.

Jeff, Randall hasn't discounted that. You have discounted the mechanism by which the change will occur. A new environment creates new selective pressures on genes affecting the way humans think and behave. As a result, more and more of the population will have behaviours and instincts that increase reproduction in the new environment.

The reason most of us reproduce is to perpetuate ourselves--more specifically, our genes.

PacRim Jim, Actually, the truth is subtly different. The reason each of us is here in the first place is our ancestors' genes drove them to reproduce. The people born in the next 200 years will be born because their parents' genes will drive their parents to reproduce.

If immortality of a sort becomes possible, will we need children? We will become our own children.

Jim, doesn't Randall's original article already answer your question. No, we will not need children--or at least not as many children. The question is: Will we somehow subvert natural selection to reverse its inevitable outcome?

Are you assuming that other factors won't affect the rates of births and deaths?

DRJ, the other factors only change the environment in which natural selection operates. Natural selection automatically and mechanically maximizes reproduction regardless of any other factors.

Bob Badour said at November 6, 2006 7:16 AM:
As they catch up technologically and culturally with the West, I expect that their birthrates will decline as well.

Christopher, I highly recommend you read Darwin's Dangerous Idea by Daniel Dennett to better understand the process of natural selection. In the short term, birth rates may decline as instincts previously selected for cease to increase reproductive fitness. In the long term, however, natural selection will simply select new instincts that cause birthrates to increase again.

Bob Badour said at November 6, 2006 7:47 AM:

To illustrate some of the points I have made, consider low-status couples and instincts that increase total fertility. Suppose for argument's sake that status seeking drives people in poor agrarian societies to have lots of children and that the new environment created by highly industrialized society causes status seekers to have fewer children.

Natural selection means that genes for different instincts will become more prevalent in the general population of industrialized societies. One might ask: What sort of instincts? While it is hard to predict a winner, I can think of one instinctive reproductive strategy that will increase in prevalence: brood parasitism.

I know quite a few people who have large numbers of children: ie. men with a dozen or more children and women with six or more children. Over 90% of those are low-status people who avoid the cost of parenting by leeching off of others. Generally, these people are considered unfit parents and the state removes the children they produce from their care. The children are then raised in foster families or adopted much in the same way other species of birds end up raising the young of the common cuckoo.

I am not saying that brood parasitism will become the dominant instinct to increase total fertility. I merely observe that it is one of many phenotypes currently competing for position.

Chris B said at November 6, 2006 7:53 AM:

Bob and Christopher,

All major populations with above TFR have sharply decreasing TFR's. With the Industrialized countries at below TFR, and China, India, and S. America experiencing sharply declining TFR's, at current trends, the world will be depopulating within a century or two.

I suggest visiting the U.N.'s website for a bigger picture of population trends.

Bob Badour said at November 6, 2006 9:31 AM:

Chris B,

I agree the evolutionary landscape has changed. The declining TFR's in some places have already started to reverse. Are you suggesting that natural selection won't reverse the trends within a century or two?

Steel Turman said at November 6, 2006 9:55 AM:

How do you balance the disparity of wealth?

The industrialized societies would be 'neutered' and the rest would continue to breed amok.

The only logistically possible way would be involuntary application of whatever agent proved efficacious.

Considering the religiosity extant today (and that shows no signs of abating), would that not be tantamount to an act of war?

And, I don't imagine a UN mandate would prove useful, either.

You COULD wait until after some virus decimates the population, reducing it by two thirds, but then you'd no longer need to reduce the population.

Programs to limit population are not working all that well in those countries that are currently trying them and
the unintended consequences are problematic.

Call me an idealist, but I suspect that population is ultimately self-limiting.

Especially human population.

Randall Parker said at November 6, 2006 12:33 PM:

Christopher Rasch,

You assume the rest of the world is going to catch up. That is not happening. Per capita GDP growth rates are widening the gap, not narrowing it. There are exceptions such as China. But the gap is getting even bigger between the US versus Latin America and versus Africa.


Good bye wilderness.

Randall Parker said at November 6, 2006 12:47 PM:

PacRim Jim,

People reproduce in order to have children. They aren't thinking they need to further the species or to achieve immortality thru their kids. They want to have kids of their own. This is an instinctual desire.

My argument is simple: Natural selection will reverse the decline in fertility by selecting for genes that heighten the desire for children. Does anyone dispute that?


You are correct, eternal youth just makes the problem come faster. Natural selection is going to work in increase the incidence of genes that favor the desire to have offspring regardless of whether we develop ways to engineer negligible senescence with eternally youthful bodies.


Avoid the mistake of thinking that just because fertility has been dropping in many countries it will continue to drop. In some countries it has already reversed. It will reverse in more countries as natural selection produces new generations with stronger instinctual desires for offspring.

Do any of you think people do not have instinctive desires to reproduce? Why do you suppose women like babies? They aren't just blank slates programmed by our culture to like babies.


Thousands of years is a very long time. People will be able to pursue 10 different careers. But why will that cause them to not want to have kids? They have kids now with just one career.

rsilvetz said at November 6, 2006 2:40 PM:

Randall -- I agree in principle that reversion to the mean is bound to happen. But which mean? There is fertility and fertility. Niger, today's champion of fertility, has a rate one-half [52 births/1000women] the historical norm [80-100 b/1000wo] that kept the species alive from prehistory to the birth of Christ.

The fact that this drop has persisted (and worsened for the rest) against a background of almost 100 generations means something. Some powerful factor is acting as a damper and I can't help thinking the uncoupling of sexual pleasure from procreation is the culprit. We are the only animal that does this. Niger offers an interesting case study for this, since the penetration of oral contraceptives is about 50%, meaning that the breeding should be bimodal, a peak of family-planning births with 2-3 children and non-family planning births running 6-8 children. I'm seeing if I can find out the real distribution.

It might be that it is not about raw fertility pressures. In the end, we are conscious, that implies choice/free-will (or at a minimum feedback loops on behavior for the determinists out there), such that in industrial society the evolutionary norm is close to replacement and we oscillate around that. (?)

Food for thought.

Dezakin said at November 6, 2006 3:29 PM:

"My argument is simple: Natural selection will reverse the decline in fertility by selecting for genes that heighten the desire for children. Does anyone dispute that?"

Yes. By the time this statement becomes realizable, the question will be meaningless. It will take many generations to realize this, and by then the shape of the world may very well be driven by populations of machines.

jon said at November 6, 2006 4:45 PM:

Something's missing from this discussion: the reasons for falling fertility.

Fertility used to be very high because many parents saw them as child labor important for the family's livelihood and prosperity: e.g., as farmers.

Nonfarm families prefer to have fewer kids, because the return is much farther off, and despite the reduction in food costs, the cost of raising children is rising rather discouragingly quickly.

There are several reasons. Labor, and thus childcare and schooling costs are always on the rise. Increasing need for longer education. High govt regulation and involvement. The increasing development of highly useful, but expensive services like disease screening in IVF-implanted embryos, and increasingly continuous testing; Grandma expects DVDs of ultrasounds these days. And of course, there are more kinds of special schooling than you can throw a stick at.

Those are all pretty powerful disincentives, especially if you're a responsible kind of parent and intend to limit your numbers of kids to what you can feel you can support in a high level of care.

These factors are all getting worse. And, in fact, these factors seem likely to make even farm kids increasingly less economically helpful in the 1st world.

imp said at November 6, 2006 5:35 PM:

This is nonsense. Population growth leads to economies of scale and greater longterm economic growth. As a result, it leads to greater technological growth. Mankind will have challenges in the future such as extraplanetary colonization, and "sustainability" hogwash does nothing to prepare us for those challenges.

Parker is spouting a political agenda. Likely an ex-post rationalization for his own less than fecund ways and choices.

Randall Parker said at November 6, 2006 5:51 PM:

Robert Silvetz,

Reversion to a mean? No, that's not how evolution works. The environment is new. Therefore the selective pressures are different than those that came before.

We have harnessed huge amounts of resources. We could give birth to many more children than we now have. Natural selection is relentless and will produce humans who will so want children that they'll accept lower living standards to get them.

Chris B,

Niger does not have a rapidly declining total fertility rate. Some countries have bottomed out on fertility rate declines and have begun bouncing back. I saw a demographer give a speech about this on C-SPAN about a year ago. This isn't surprising. It is what Darwin would have predicted.


Schooling costs will not always go up. Education will become automated. But the economic costs that are disincentives for having large families are not disincentives for everyone. Those who have children in spite of the economic signals are obviously responding to other signals. Those are the people to watch.

Randall Parker said at November 6, 2006 6:10 PM:


If people retain their human instincts they will reproduce.

I do not see space colonization as a solution to natural selective pressures. Space colonization really means solar system colonization. Once we can do that it will provide some more space for a while. But that too will be exhausted eventually. Once we use up all the mass in this solar system the cost in mass and energy to move us to another solar system defeats the purpose of leaving in the first place.

Wolf-Dog said at November 6, 2006 6:26 PM:

"I do not see space colonization as a solution to natural selective pressures. Space colonization really means solar system colonization. Once we can do that it will provide some more space for a while. But that too will be exhausted eventually. Once we use up all the mass in this solar system the cost in mass and energy to move us to another solar system defeats the purpose of leaving in the first place."

By the time we attain immortality, it will be at least 100 years. And after that, the level of intelligence will be enhanced dramatically, so that the new generation will not think like we the primitives do:) Thus nobody knows how exactly people will be thinking after 100 years, but Steven Hawking stated that genetic engineering will increase the complexity of the human race in the future.

Thus it is also quite conceivable that the human organism will become so much more efficient that its existence will require less space. Perhaps the human mind will sustain itself in an electromagnetic field, with minimal need for organic material. It will perhaps be possible to circumvent the "human analogue of Moore's Law", and perhaps optical and electromagnetic computing will allow trillions of humans to get compressed in a cup of water. As if this were not enough, I also disagree that the colonization of the solar system will be the end of our territorial expansion. Nothing can be further from the truth. Space travel will be accelerated by totally new propulsion systems after a few hundred years, the laws of physics will expand into new realms.

Randall Parker said at November 6, 2006 7:44 PM:


Sure, if the human race goes extinct due to a take-over by machines we won't have to worry about overpopulation. But I would rather focus on making sure machines do not take over and then try to solve the problems that'll come from how humans respond to and use technological advances.


Your decision to have kids was the result of instinct. Your instinct was not strong enough to make you want 5 or 6 kids. Others in similar circumstances but with stronger instincts have more kids.

Randall Parker said at November 6, 2006 7:46 PM:

Julian Morrison,

Those with the strongest instincts to reproduce will oppose this proposal very intensely. That's a problem. I think the odds are against my proposal precisely because human instincts are against it. But the alternative is not going to be pretty.

Doug Dante said at November 6, 2006 9:16 PM:

"World overpopulation is one of the biggest problems ...."

The hidden presumptions in the article are:

1) We humans can't leave the world - i.e. Earth

2) There is some relatively small number of humans, probably no more than 2x today's world population, that can live on the Earth sustainably, and it's impossible for future generations to increase this faster than their rate of unaltered population growth.

100 years ago we were just beginning to fly. Can any one of us guarantee that 100 years from now we will not have cheap transport to space habitats that can house our excess population?

Our environmental technology is rapidly improving, but still in its infancy. Can we be sure that we can't double or more the effective carrying capacity of human beings on Earth in the next 100 years, e.g. through the creation of urban archologies, exclusive use of wind and solar, recycling of waste water, composting of human waste, and the elimination of non-biodegradable and non-recyclable products?

We can't be sure these things aren't true.

If we're not sure about the next 100 years, how can we be sure about the 100 after that?

Why fret about a non-issue?

rsilvetz said at November 6, 2006 11:50 PM:


"Reversion to a mean? No, that's not how evolution works. The environment is new. Therefore the selective pressures are different than those that came before."

Galton, Charles Darwin's cousin, would disagree. Reversion-to-the-mean is an essential aspect of natural selection. It's what provides stability for the species and I submit to you that it the other half of the evolution coin. This is why the prediliction of women for tall men does not result in runaway height*. It is EXACTLY what supports your idea that birth rates should rise without any hand-waving of unspecified selective pressures. Because, it's just as likely it could be going the opposite way. Selective pressures could be sanctioning low-birthing women every bit as much as high-birthing women.

In fact, I submit to you that is more likely what the last 2000 years have done. Applied to the problem at hand, if raw historical fertility rate is north of 10 and Niger is running 7 with the species running 2-3ish, we should have reverted with a bang a long-time ago. It's been dropping since Rome ruled the world. We haven't reverted... against immense odds... and what does that say to you? And what does that imply for Niger... namely that it can't last...

In point of fact we are on the same page, only in opposite directions. I've given the thread a table showing that we are running below half-normal or worse for any large subset of the species and that we have been doing so now for millenia. My message is that a fertility rate of 6 or 7 is really no big deal historically. In fact, it's low. What is important is that we crushed infant mortality and thus have a planetary population boom.

You're right in that any postive fertility rate in the face of immortality adds massively to population. But it's a non-issue because if they are producers/creators we will all be fine.

Ok. Dead horse duly beaten. See y'all next week.

(*) Galton,F. 1886, "Family Likeness in Stature", Proc. Roy. Soc. London, vol 40, pp 42-73

Brett Bellmore said at November 7, 2006 4:19 AM:

"Surely instinctive desires for children exist in our DNA"

I think not. We have instinctive desires to have sex, and in a pre-technological society, having sex leads to having children. Then other instincts kick in to make sure you raise 'em instead of drowning them.

But instincts to "have children"? Nope, I see no real evidence of an instinct instilling that high a level goal.

Bob Badour said at November 7, 2006 8:52 AM:


Natural selection has only one outcome and no goal. It increases the prevalence of genes that improve reproductive fitness in the current evolutionary landscape. By ascribing it a "goal", one anthropomorphises a very mechanistic process.

Instincts to have sex and instincts not to drown the offspring are instinctive desires for children. However, having met and having seen interviews of teenaged girls who actively want to become pregnant by any means possible, I suggest at least some of the population have genes that drive a direct desire to reproduce.

Dezakin said at November 7, 2006 2:01 PM:

Again people, think about how many generations it will take for these 'active reproduction desire' genes to replace/augment the sexual pleasure genes in the human population.

By the time they do, humans born the old fasioned way will be in direct competition with humans who copy themselves to more machines. The old fasioned reproduction doesnt have a chance in winning this race. The future shape of civilization is in the hands of machines.

Bob Badour said at November 7, 2006 2:53 PM:


Assuming rejuvenation, the genes will never 'replace' those in the founding population because the founding population will hang around forever.

I believe someone pointed out that a 1% reproductive advantage would become ubiquitous in the human population in less than 1000 years. A heritable trait that causes one to desire conceiving lots of children would give one far more than a 1% reproductive advantage--perhaps more like a 300% advantage.

How many generations would that take? Let's see, if a dominant trait causes one to have 6 children at an average age of 20 years, in 300 years one will have 14 million descendants with the gene in the youngest generation (assuming half of the offspring in each generation inherit the gene.) With rejuvenation, all of the generations will still survive giving over 21 million descendants carrying the gene.

However, that does not take into account the effect rejuvenation will have on total fertility: If someone with the gene has 6 children while young, what would happen when a still-youthful, still-fertile 45 year old faces an empty nest? Such a trait may cause the person to have even more children.

Dezakin said at November 7, 2006 3:03 PM:

You still aren't getting me. 300 years for some 21 million decendants is still at least 150 years too late to compete with the trillions of trillions of machines crawling for resources, that are better equiped to utilize them. Flesh and blood humanity cant win.

Randall Parker said at November 7, 2006 5:04 PM:

Doug Dante,

Travelling between planets takes far more resources than travelling between continents. Even if we assume a space elevator and enough energy to move people out to Mars how many people will want to live on Mars even after it is terraformed?

We could pull in lots of materials from asteroids and build up space habitats. But space has high radiation and contained spaces will be small compared to continents.

But even if lots of people are willing to move to terraformed Venus and Mars and even if we have the technology to move them how does that help? It pushes off overpopulation by a couple of generations at best. But people won't be willing to even go off-planet in large numbers until the crowding here becomes really bad.

Randall Parker said at November 7, 2006 5:17 PM:

Robert Silvetz,

The selective pressures for higher fertility that I speak of are not unspecified or hand-waving. Fertility has dropped. Yet humans have enough resources to support far more offspring. Those who have alleles that make them have more offspring will have their alleles increase in frequency in future generations.

Fertility has not steadily dropped since the Rome Empire. It has gone up and down depending on conditions.

I expect the human population of the world to rise into tens and even hundreds of billions if natural selection is allowed to run its course.

Bob Badour said at November 7, 2006 6:26 PM:


You are not getting me. Those 21 million hypothetical descendants are from a single individual. Current evidence suggests millions of Americans have genetic traits that increase the desire for children. If 1% of the US population have a genetic trait similar to the one I hypothesized, in 300 years there would be a maximum of 63 billion descendants with those traits, which is nearly 10 times the current population of the entire earth.

Worldwide, as Randall's latest blog article points out, there are about a billion Muslims who exhibit higher fertility with no valid reason to think it will decline. Those 21 million descendants of a single individual then make a maximum of 21 trillion muslim descendants. Granted, the actual number will be smaller than 21 trillion due to inbreeding and the apparent habit of muslims killing lots of other muslims.

Ivan said at November 8, 2006 8:21 AM:


I think you are off by orders of magnitude on your estimates of the resources of space.

There is space for millions of earth-surface-areas, and the surface area of a dyson's sphere is the logical extent of the energy capture potential of our solar system.

"But space has high radiation and contained spaces will be small compared to continents."

So, I disagree. Space in space will be large compared to continents. I'm not talking about SpaceLab-1 here. I'm talking closer to ring-world.

Sci-fi today, but not with semi-efficient solar power and a space elevator.

Dezakin said at November 8, 2006 4:21 PM:

Naive extrapolation and curve fitting run amok. If there was a gene that made people successfully produce 6 successful offspring per woman, we could have this conversation. There isn't; theres trade offs in genetic variability. Higher desire to have children often corolates with inferior resource utilization which influence things like child mortality. Oh sure, we have selective pressures, but we dont have infinite resources, and these changes take time.

"I expect the human population of the world to rise into tens and even hundreds of billions if natural selection is allowed to run its course."

Sure, but it wont. We're at the dawn of the age of machines, and at the twilight of humanity.

rsilvetz said at November 8, 2006 7:07 PM:


Do you disagree with my posted table of births/1000 women per various historical period?

If you don't, the assertion that the overall 2000-year trend is one of long-term decline stands as dose the reversion-odds estimate. In which case the long-term trend is one of a stable replacement society in the tens of billions.

If you do, give me an alternate table to work with and perhaps we can close the gap. I've already shown that the fertility champion Niger is nowhere close to what women were doing prior to Christ.

And to those with the Terminator:Judgement Day syndrome, what on Earth makes you think we will crack Artificial Intelligence/Life before we crack DNA repair? One problem is orders of magnitude harder than the other!

Bob Badour said at November 8, 2006 7:50 PM:
Naive extrapolation and curve fitting run amok.

I offered the example for illustrative purposes only, and I maintain that it very clearly illustrates the point.

Higher desire to have children often corolates with inferior resource utilization which influence things like child mortality.

Did the horse really need flogging? I already ceded that the actual number would work out to something less. Thus, if the figure is out by a full two orders of magnitude, the muslims would only engender 3 times the earth's current population in 300 years. But then again, that's only the muslims. What about the catholics?

We're at the dawn of the age of machines, and at the twilight of humanity.

What was that about naive extrapolation and curve fitting run amok?

Dezakin said at November 9, 2006 1:17 PM:

"And to those with the Terminator:Judgement Day syndrome, what on Earth makes you think we will crack Artificial Intelligence/Life before we crack DNA repair?"

Nothing. It doesnt matter if we do DNA repair and perfect health today and dont do AI for the two hundred years. AI simply has a far more efficient reproduction strategy.

TomC said at November 29, 2006 1:09 PM:

The most effective counter to desire to have children... is to have some.

The number required to shut down any instinctive desire to reproduce will vary from person to person - for some, merely being an aunt or uncle is sufficient, for others, "eight is enough", and a very few seem to feel kids are "cheaper by the dozen". But eventually grandkids come along and that cheaper "fix" for infant-addiction, combined with memories of the reality of child-rearing, will almost always be sufficient to shut down the reproductive urge.

As a result, once life extension becomes practical, we'll find that the reproducing fraction of the population will drop steadily until eventually zero growth will be hit as suicides match births. Population will likely grow until that point is reached.

In fact, we'll probably find that for the first century or so after full control over bodily health is possible, population won't grow nearly as fast as it could, as people who grew up thinking that death was inevitable, and perhaps are infected by 'death = heaven' memes, find ways to shuffle off this mortal coil. Not simple suicide - more likely it'll be a death-wish, expressed as exuberent risk-taking "celebrating restore youth", by people who don't realize that they feel guilty about having "cheated God".

Eventually we'll have many alternatives to suicide - uploading, suspending animation with periodic revival if anything interesting happens. Perhaps even an implementation of reincarnation, by allowing an uploaded mind to experience life "from scratch", with memory of previous lives slowly integrating as the child grows older.

Mike said at January 14, 2007 8:32 AM:

One aspect of this unaging society might be the inability to change it's mind. Unending years of the same old same old. Children bring more than physical renewal, but a new way of looking at things. . Today , many people substitute children with pets. Imagine a future where this was the norm. Finally, a primal reason we do the things we do is to reproduce, and provide the resources for that. Is it possible to remove this aspect and retain the desire to explore, find new things, or will we finally become drones in truth, doing the bidding of the remaining few who can reproduce?

oris said at April 7, 2008 4:40 AM:

what is the status of overpopulation in the third word countries

Josh said at February 11, 2009 5:01 PM:

Randall, I agree with you. I came to the same conclusion myself after I saw a documentary about women who were serial surrogate mothers. One had 11 babies through in vitro, another had 8 babies through artificial insemination (so they were biologically hers); they admitted to being "addicted to pregnancy." It occurred to me that people like that would eventually dominate the population in the future, along the same line of reasoning as yours. I can see some people here are missing the point, though...

Knowledge is power said at November 13, 2015 4:46 PM:

I have read allot of articles on this topic for the last 5 hours and In conclusion after reading an unholy metric fuck-ton of comments and ideas
that people have posted I have decided to post my own views and collectively gather all I have read into a single entity so that people may
get the Omniversal views of all who shared their views as well as my own views and ideas on this topic.
#1 So first off to those of you who just randomly searched up something that lead you to this, This topic is about immortality. So before we
get into the The logistics of how, why, and when Let us First clearly define (Immortality) According to Wikipedia Immortality is

("The ability to live forever; eternal life") This is referring to Eternal Life,never ageing not (Invincibility) please do not confuse the two.

Now as allot of debates on this subject clearly depict there are actually two types of immortality The first being that of a spiritual one. Where your spirit never dies that when your body dies your spirit simply sheds itself of it's former body like a piece of clothing and is reincarnated into another life(The Buddhist view of afterlife and death) Or perhaps one of the many monotheistic religions Such as Judaism, Christianity, or Islam where when your body dies your soul leaves your body and is placed in either Heaven,Hell,or (Purgatory based upon the Roman Catholic view of afterlife) Where you are placed is a matter of how well you preformed in your life according to That specific religions rules and guidelines. .Finally when your body dies according to the Greek's polytheistic view of gods and goddess when your body dies your spirit either goes to Elysium or Tartarus Where your spirit goes is dependent upon how well you preformed in life according to That specific religions rules and guidelines. Now upon reading this article you have seen or should have seen the connection these seemly vastly different religions and timelines all have. They all support the idea that (a) or (the) (Spirit or Soul is Immortal)and cannot die,perish, be consumed or otherwise destroyed. Therefore With all religious views in agreement we can definitely agree that Our souls are immortal. (Sorry Atheist people)

#2 So now that we have covered spiritual immortality what about physical immortality? 60 years ago this article along with the internet and everything this article represents would have never even been contemplated let alone online published for you to be reading it right now. However as the pendulum of time swings ever in motion new inventions and innovations come to become a reality such is the way with advancement momentum. Every 18 Months our computing power roughly doubles that of it's former self. As with all things in this last century Bio-engineering has been rapidly advancing and evolving itself in new and innovative ways such as nano-bots.These tiny little robots are currently under experimentation on animals for the purpose of finding hazardous cells or objects such as cancer or blood clots and attach themselves to hazards and alerting you of the hazard at the soonest possible moment.

These little Robots are just one example of how lives that would of been lost 10 years ago can now be saved by Bio-Engineering. Among other things such as the invention and practical application of Genetic DNA Scissors in 2012 which allows tacticians to modify Our genetic sequences feats only dreamed about in the 1970-1980.Along with the development of stems cells which allow one to regrow a missing limb or an organ. As we continue in our unique paths of destiny we each add our own piece of the puzzle that will ultimately lead to immortality. So one way or another is immortality within our grasp? Yes indeed it is I truly believe that we can achieve immortality within the next 20-40 years the question is no longer about whether or not it's possible to achieve immortality but Will we? and if we do what happens tomorrow.

#3 Now that we have firmly established immortality is a very possible feat in the near future what will we do? No matter where you come from or where you may have initially heard of the concept of immortality since the beginning of time all around the world there have been myths and legends of immortal gods, Beings, And even other Humans that have dabbled in dark magic or evil pacts with demons or even the devil to obtain immortality.

("Magic is just science yet to be explained") So there you have it are there any immortals watching us right now as we steadily progress towards immortality Ourselves? I Suppose only time will tell. Much of the truth of immortality is shrouded in darkness or common place misconceptions. However the general view of Immortality is a rather dark and grim cursed existence. Watching, sitting around alive and young while your children and anyone you have ever loved grows old and dies Truly dead to the world. However that may be so for one who acquired immortality from one of the above mentioned methods what would immortality be like if everyone was immortal? I can name a few movie titles that have a similar concept to this one of them is called "Time" The other is called "Elysium". (Huh guess the Greeks had it right after all) So What do you think it would be like let me know in the reply's below.

#4 So now what? What happens tomorrow? Everyone is immortal and continuing to have babies and since no one wants to stop having sex and kids The population is now starting to exceed the maximum limit that the earn can sustain. No one ages so no more death from old age So that tallies death up to disease, accidents, and wars. Well with immortality achieved i doubt there are very many diseases left around that could seriously start dropping a body count. Your now immortal now so you have allot of time to practice anything and everything extensively so i doubt very many accidents will happen now and everyone wants to live forever and will start to realize material goods are worthless when you are eternal so i doubt war will happen very often either. So how do we lower the body count? Well I see only 4 options here either you put a 1 child per 5000 years limit, everyone turns completely single forever, everyone turns gay forever,or we start colonizing space. Which leads us to number 5

#5 So we fixed the whole not dying overpopulation issue by colonizing space and putting up that whole 1 child per 5000 limit so were all good right up until we run into other alien explorers/Colonizers like us and ......? I never understood the entire argument about other spaces people all it all ever states is that we 'May' run into aliens on our path colonizing the stars.This is Extremely Unlikely as the universe is both unfathomably massive and endless as existence itself. As well as a moot point because in all actuality if we did find another explorer like us we would A work with them B Avoid them C Wait them out since you know the whole were Immortal thing or D Kill them so the whole running into another alien argument is entirely moot and pointless. Eventually we wouldn't even need substance to sustain ourselves as we further continue to modify our genetic code we could very all well eventually reach a point in controlled evolution that we no longer need bodies at all and once that happens none of this will concern anyone anymore ever again.

#6 So This has been A really fucking long article on this topic I have been researching and reading everyone's comments , ideas, and views on the Issue of Immortality and I have done my very best to compile all the evidence of such a possibility happening in the near future from various sources. Integrating all of the various peoples views and comments that I found interesting or enlightening and dashed in a side of my own personal views and opinions.

Please tell me what all you think in the replies below and if there was anything I should of added in i left out and if there are any spelling mistakes or grammatically incorrect sentences I am sorry I have been reading this subject for like 5 hours and writing it for about 3 now Anyways Peace out and Follow your path of destiny to immortality. "Carpe Diem"

'Knowledge is power the Universe is Simply waiting for you to grasp it' my own quote :)

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