June 23, 2009

Generation Length

Here's a simplified thought experiment to demonstrate the impact of generation length on the size of future populations:

Two babies girls are born today. They both will give birth to twins and to no other children, so their lifetime fertility will be at the idealized replacement rate of two. The only difference is that Tiffany will give birth to her twins at age 24 and Emma at age 32. Their descendants will continue these patterns: giving birth to twins at either age 24 or 32 years apart. Ninety-six years in the future, Tiffany's 16 great-great grandchildren and Emma's 8 great-grandchildren will be born.

My published articles are archived at iSteve.com -- Steve Sailer

48 comments:

agnostic said...

"Tiffany" being a recent #1 name among Black daughters.

simon said...

If life expectancy is proportionate to generation length, both populations will remain the same size, though.

The main impact of shorter generation length is as a force multiplier for greater fertility. If you have 20-year generations and 4 children you double the 20-year-old age cohort every 20 years; if you have 30-year generations you double every 30 years.

dearieme said...

I tried long ago to explain the generation-length idea to a Maoist, justifying my claim that China's "one child" policy was unnecessary. As you might expect, he was too thick to understand.

William 1066 said...

If both family groups are reproducing at the replacement rate then, at equilibrium, the only impact the 24 vs. 32 age of the mother should have is the number of generations existing at the same time. That is, assuming they all die at 96, then the 32 year mothers would have three generations co-existing while the 24 year mothers would have four generations.

On the other hand, if the mother each have three babies, then there will be no equilibrium and the 24s would soon greatly outnumber the 32 group.

Anonymous said...

Man.........even I didn't know that.



There is a reason demography is never taught in schools. Boy is this country going to be swamped in the future. If I were an evil billionaire, bent on payback, I think I'd open a bunch of chicken processing plants and other illegal-alien-ridden businesses right outside of left-wing strongholds like Boston, Manhattan, Baltimore, D.C., Seattle, and everywhere else that I could detect much of the DNC/Moveon.Soros money came from. I'd love for these people to see what they are building for their grandchildren up close and personal before they get it. I'd enjoy, Lawrence Auster-like-reading newspaper artilces online from these cities mentioning crimes that mysteriously had no assailants, just "someone was shot" or "a boy was knifed", that demonstratively used Gramascian/Marcusian politically-correct-cultural-marxism to hide how lousy these-once-nice towns had become.

I'd make a special effort to wreck the small town of Crawford, Texas also. If I couldn't get at least 100 MS-13 members to calll that place home, I'd be dissapointed. Im aware of the fact Im such a meanie. m

henry harpending said...

But notice that the numbers of fractional copies of Emma's genome and of Tiffany's genome are exactly the same

J said...

What is Tiffany drops out of school and gives birth at 16 and Emma completes her Ph.D. and marries at 35? If the pattern continues, you have .. how much?

dr kill said...

That ain't nothing. When I lived in Riyadh, Mastercard ran an advert that featured an obviously Indian family-

Five generations in one photograph? Priceless.

Indeed.

Forget the Chinese and their totalitarian and one child country. India will pass by our economy like we are tied to a tree. The Reds won't even get a sniff.

Anonymous said...

So if Maria gives birth to 4 kids at age 16, does that mean she will have 128 great-great-great-great-grandchildren in 96 years?

John Carr said...

Steve,

I take it you've oversimplified for effect. In a developed country the replacement rate is about 2.1 as (a) not every girl survives to reproduce and (b) more boys are born than girls even without sex-selective abortion.

Anonymous said...

Exactly. And guess who are having kids late? College educated white women, that's who. I'm one, and I'm now 59, w/ 3 children and no grandchildren. I work w/ women my age, both races, who are not college educated. They have grandchildren as old as 15. If you have your first child at 20, and they have a baby at 20, then by 40 you're a grandmother, and by 55, you have a 15 year old grand child, and by 60, you'll be a greatgrandmother. This is really happening.

Fred said...

Steve,

OT, but have you looked into the fatal commuter train crash in D.C.? The conductor was apparently a 42 year old black single mother, with only a few months of experience. It would be interesting to know if she was an affirmative action hire and if her error helped lead to the crash.

JeremiahJohnbalaya said...

Willaim 1066 said If both family groups are reproducing at the replacement rate then, at equilibrium, the only impact the 24 vs. 32 age of the mother should have is the number of generations existing at the same time. That is, assuming they all die at 96, then the 32 year mothers would have three generations co-existing while the 24 year mothers would have four generations.

You are confusing terms. The "replacement rate" takes into account the length of the generations, among other things. All other things being equal, the group givnig birth more often (ie. 24 years versus 32 years) has a higher "replacement rate"

Anonymous said...

You are a racist thought criminal for even mentioning this. These are hate facts.

The sooner the liberals breed themselves into minority status, the sooner we can return to sanity as a country.

William 1066 said...

By replacement rate, I mean the number of births per woman that (eventually) leads to a stable population size. This number may be around 2.1. All else being equal, the rate does not change with the generation length. In equilibrium the generation length only determines the number of co-existing generations.

One thing that may cause confusion is comparing the number of Tiffany and Emma's offspring, but for different generations. This makes for apples and oranges - note that Tiffany's 16 great great grandchildren would each have 1/16 her DNA while Emma's 8 great grandchildren would have 1/8 - and adding it all together you still get a total of one Tiffany (or Emma) in each generation. Alternatively, Tiffany is only one of 16 great great grandparents, while Emma is one of eight great grandparents. It took twice as many ancestors to get those 16 ggg as it did those 8 gg.

Anonymous said...

I know a certain very bright Mormon family. Very mathematical and musical. All five kids married at young ages and began popping them out. E.g. the smartest of the lot is a 30 (male) math professor and has three kids.

We should be encouraging secular/Protestant smarties to follow the Mormon model.

Nanonymous said...

But notice that the numbers of fractional copies of Emma's genome and of Tiffany's genome are exactly the same

But if both Emma and Tiffany and their offspring mate assortatively then Tiffany's genes are a lot more evolutionary fit.

Anonymous said...

"The sooner the liberals breed themselves into minority status, the sooner we can return to sanity as a country."

Assuming that the children of high-birthrate conservatives remain conservative.

::eyeroll::

Does Bristol Palin seem like a conservative to you?

Media uber alles.

Anonymous said...

"What is Tiffany drops out of school and gives birth at 16 and Emma completes her Ph.D. and marries at 35? If the pattern continues, you have .. how much?"

I have been belaboring this point for years. Thanks, Steve, for making it more public. I read it first in a Garrett Hardin essay.

The age at which women begin producing their children matters even if the number that they produce isn’t excessive.

Take, for example, Woman A, who postpones children until she is 30 to pursue education and passes these cultural values on to her children. Then take Woman B, who begins bearing children when she ends her education at 18 and passes these cultural values on to her children. If we restrict the number of children per generation to 2 and the years between births to 2, we can quickly see some major demographics.

The second generation isn’t too dramatic. By the time that Woman A has completed her family at 32, Woman B still has only her 2 children, born when she was 18 and 20. Then it starts to get interesting.

By the time that Woman A first becomes a grandmother at 60, Woman B has 4 grandchildren and 8 great-grandchildren. That makes 3 descendants for Woman A at age 60 and 14 for Woman B.

Let’s assume that they both live into their early 80’s. By the time, she dies at 83, Woman A will have produced 2 children, who will have produced 4 grandchildren, making her descendants total 6 at her death.

Meanwhile in this same 83 years, Woman B will have produced 2 children, 4 grandchildren, 8 great-grandchildren, and 16 great-great-grandchildren for a total of 30 descendants.

The difference between 6 and 30 is quite remarkable. Needless to say, if you lower the age at which Woman B begins her childbearing even a couple of years and raise her number of children to 3 or 4, “demographic change” can kick in very quickly.

D Flinchum

Anonymous said...

"I'd love for these people to see what they are building for their grandchildren..."

They're building it for mine, actually.

Anonymous said...

"We should be encouraging secular/Protestant smarties to follow the Mormon model."

They helped put us here. I welcome their demise.

rec1man said...

I have seen this phenomenon in the muslim ghettos of Hyderabad, India

The girl at 15 - married ( to visiting Arab Sheikh tourists )and pregnant
Her mother at 30 - married and pregnant
Her grandmother at 44 - married and pregnant

3 generations giving birth at the same time, with the goal of islamic demographic takeover

Richard Hoste said...

Wow Steve, I never looked at dysgenics from that perspective.

Thanks, you ruined my night.

Sideways said...

Read something over the weekend that this reminded me of. The oldest man in the world died in Japan Friday at 113.

He had 8 children. Those 8 children had 25 children. Those 25 children had 52 children. Those 52 have had... 6 children. Really illustrated both the falling birth rates and the slowing of the generational cycle in Japan.

Anonymous said...

Lets compare across cultures. Raheema has an arranged marriage at age 15 and produces a child every 2 years until she is 45. Meanwhile, Megan completes her masters and then her Phd and goes on to a lucrative corporate career and finally gets around to having her first child at age 40 and decides one is enough. I think I see where this is going in a few generations...

Anonymous said...

Statistics leaked to the press in London, England indicate that 51% of schollchildren do not speak English at home.
By today's standards, 51% doesn't sound too dramatic, but let's dig a little deeper.A huge proportion of London's population is in fact of carribean descent - and they speak English as the mother tongue, another huge proportion is mixed race black/white, again English speaking.Add the fact th mass immigration has been going on for so long now that threre must be as least as many 2nd and 3rd generation non-White children in London as there are 1st generation.
Combining all this, it is very likely that 80% of children in London are non-White.This number will only increase in the future.
Furthermore, the majority of Whites in London are in the old to elderly bracket and presumaby will pass in the next few decades.
The upshot is that London's demographic revolution will be very, very rapid and with an accelerating trend to the point where in a generation or so Whites will be a distinct rarity on the streets of London - a proposition unthinkable 50 years ago.

Anonymous said...

Gulp. This doesn't end well at all.

Anonymous said...

I accidentally put this comment on the wrong comment thread. So, I am resubmitting it here.

This topic is covered in the film, Demographic Winter.

The film explains the impact of falling fertility on prosperity.

The goal of avoiding overpopulation seems reasonable. The current situation suggests that those most willing and most able to change behaviors to more sustainable modern lifestyles are also the people who are decreasing quickly, while those lacking the interest and ability to help develop sustainable lifestyles are increasing.

Zimbabwe.

pzed said...

But if both Emma and Tiffany and their offspring mate assortatively then Tiffany's genes are a lot more evolutionary fit.

if tiffany's genes are more evolutionarily fit b/c she reproduces at a younger age and assortatively mates, then why is anyone complaining?

if you meant to say emma's genes (and her kids mates' genes)are more fit, well apparently they aren't b/c the environment is selecting against them.

Lucius Vorenus said...

Anonymous: Statistics leaked to the press in London, England indicate that 51% of schollchildren do not speak English at home.

Do you have any sources for that?

BTW, the very same thing appears to be happening just north of the border, in Toronto:

Explosive, super-secret Toronto demography report
spengler.atimes.net

A survey of Grade 7 to 12 students finds 42 per cent of high school students were born outside Canada and East Asians and South Asians make up a larger proportion than whites...

Say hello to Sharia Law.

And don that Burka.

PS: Canadian immigrants from the Pacific Rim have extinction-level fertility rates, just like their sistren back home:

Report on the Demographic Situation in Canada
128 PAGE PDF FILE
statcan.ca

...With a total fertility rate of 1.94 children per woman in 1995-1996 and 1.70 in 2000-2001, visible minority women had higher fertility than non aboriginal women in the rest of the population for whom the figures were 1.63 and 1.51 children per woman. The total fertility rate of Aboriginal women was 2.86 and 2.60 for the same years. There were significant fertility differences among the various visible minority groups. Fertility rates were highest for women belonging to the Arab and West Asian groups, with a total fertility rate of 2.60 and 1.99 children per woman in 2000-2001. On the other hand, Korean (1.30), Chinese (1.23) and Japanese (1.18) women had lower total fertility rates than the national average...

Compare:

IQ and the Wealth of Nations
en.wikipedia.org

Hong Kong: 107
South Korea: 106
Japan: 105
Taiwan: 104

List of countries and territories by fertility rate
en.wikipedia.org

Japan, UN: 1.27
Japan, CIA: 1.22
South Korea, UN: 1.21
South Korea, CIA: 1.20
Taiwan, UN: N/A
Taiwan, CIA: 1.13
Hong Kong, UN: 0.97
Hong Kong, CIA: 1.00


The Derb says that Pop Culture is Filth.

I say that Modernity is Death.

Anonymous said...

"OT, but have you looked into the fatal commuter train crash in D.C.? The conductor was apparently a 42 year old black single mother, with only a few months of experience. It would be interesting to know if she was an affirmative action hire and if her error helped lead to the crash."

Virtually all the DC metro drivers are black. They dont' need AA. Non-black drivers would though.
Possibly there is an AA trak for females, but I doubt it any special consideration had to be dredged up to hire her. As a previous bus driver and nursing student (no info on her performance in these areas) she was as good a candidate as any.
I ride the metro every day and have been in the first and last car between Ft. Totten and Takoma countless times in the last 30 years.

My guess is cell phones were
Iinvolved.

John Seiler said...

How'd women get roped into "feminism," anyway? Our grandmothers had kids starting early, commonly at 18-22, and were a lot happier than modern women. For one thing, our grandmas weren't strapped with tens of thousands of dollars of student loans to pay off from worthless P.C. college degrees.

Andrea Freiboden said...

History is 'written' by those who decide what can and can't be discussed. Steve Sailer wrote a book on Obama, but the MSM and mainstream academia will not discuss it, and therefore, most people will never hear about it.

Same with crime. Most people never heard of the Knoxville Massacre whereas we all know about Emmitt Till because one is openly discussed and remembered while the other can only be found through search on the web.

Eric said...

How'd women get roped into "feminism," anyway? Our grandmothers had kids starting early, commonly at 18-22, and were a lot happier than modern women.

Hard core feminists come from the Marxist tradition that sees every action in terms of power struggles between groups. The happiness of individuals isn't something they spend a lot of time worrying about.

Simon said...

anon:
"Combining all this, it is very likely that 80% of children in London are non-White"

A view from the front line:

In the local schools in my part of London around 1/30 of the pupils are white, going by a rough head count. But most middle class whites have kids, who you see in the play grounds, then move from London when they reach school age, or send them to private school. Also there are a lot of east European kids who are about to be old enough for school - my 2 year old son got attacked by a Russian 3 year old in the play ground today. Luckily my son is part Finnish and built like a champion wrestler, so he was unperturbed.

I am worried about what happens when he goes to school and is dealing with knife & razor wielding Somali 8 year olds, though.

The trends overall are pretty complex. I'm sure that indigenous British are a small minority in London schools; and the Irish population has decreased. A fair number of Poles have gone home, albeit many seem to be staying. OTOH those Russians are immigrants from the Baltic Republics and they sure as Hell aren't going anywhere. The same NHS that helps the Somalis pop out 8 kids apiece helps abortion-scarred Russian women have 2-3 kids, and those kids are tough little scrappers.

Overall though, in demographics terms the Somalis have got to look like the winners. They're terrorising the poor al Qaeda wannabe Pakistani street gangs in my neighourbood - not much Islamic solidarity there. The current Somali teens are the children brought here not long ago; when their UK born siblings reach maturity I think it's going to get really nasty. Pakistanis, Brits, Russians - without getting seriously organised, none of us are going to do well. And if the Arab radical preachers incorporate the Somalis & Pakistanis successfully into a broad pan-Islamic front, London will be as Muslim as Leicester.

simon said...

pzed:
"if tiffany's genes are more evolutionarily fit b/c she reproduces at a younger age and assortatively mates, then why is anyone complaining?"

Being evolutionarily fit - good at reproducing - carries no moral weight. AIDs and Herpes are evolutionarily fit, if they reproduce above replacement weight. The Shakers were evolutionarily unfit, but they made some nice tables. Rats and rabbits are evolutionarily very fit, while pandas, not so much. Doesn't mean pandas are bad or should be exterminated.

Anonymous said...

"...abortion-scarred Russian women have 2-3 kids, and those kids are tough little scrappers."

Good, we're gonna need them.

Anonymous said...

"I know a certain very bright Mormon family. Very mathematical and musical. All five kids married at young ages and began popping them out. E.g. the smartest of the lot is a 30 (male) math professor and has three kids. "
_____________

this is very true. I am not Mormon but I travel to utah often on business. The mormons seem successful at getting young people to marry early and have lots of kids.

I am thinking that if I want my three young daughters to grow up, find good husbands when they are 18 or 19 and produce a very large number of grandchildren for me that perhaps my wife and I should convert to mormonism?

I mean, overall I know of no other religion in the usa that I can possibly join that has as good a track record of producing economically productive, patriotic young people that get marrried young and produce four or five kids each.

If anyone else has a better idea please share it

Bookslinger said...

someone wrote: "We should be encouraging secular/Protestant smarties to follow the Mormon model."

someone #2 wrote; They helped put us here. I welcome their demise.

Does your "they" refer to the secular/Protestant smarties or the Mormons?

------------------

Non-Mormon dad wrote:
"I am thinking that if I want my three young daughters to grow up, find good husbands when they are 18 or 19 and produce a very large number of grandchildren for me that perhaps my wife and I should convert to mormonism?"

Participation in all Mormon programs (outside of the temples) for young-children, teens and adults is open to all whether you officially join or not.

Ronduck said...

"We should be encouraging secular/Protestant smarties to follow the Mormon model."

They helped put us here. I welcome their demise
.

Protestants did this? What about Ted Kennedy? What about all of those Evangelicals that have been fighting the culture war?

Not the father of a multitude said...

When Emma is 64 as a prudent middle class retiree she can fund 529 plans for her 4 grandchildren which would seem more appealing to a middle class educated person than having a more grandchildren and great grandchildren than she could reasonably get to know well. Racking up raw numbers is not as attractive as doing one's best to insure that none of the grandchildren fall into poverty. Think of it this way: if raw numbers really mattered there would be first world men deliberately traveling the third world to father as many children as possible. This would provide genetic variation among the descendents and the children who flourish would be tougher than pampered first world children. The cost would would be the suffering among the less successful children and nobody really wants that.

Anonymous said...

"If anyone else has a better idea please share it."

Orthodox Jewry.

Anonymous said...

Does your "they" refer to the secular/Protestant smarties or the Mormons?

The former.

Anonymous said...

"Protestants did this?"

As I said, they certainly helped, and are far more culpable than most. I don't think it's a point of debate here at Steve's blog.

"What about Ted Kennedy?"

What about him?

"What about all of those Evangelicals that have been fighting the culture war?"

Some portion of the folk want a little more out of their broader racial group than poorly-dressed halfwits getting bonked on the head by Benny Hinn and quoting the
Torah and anathematizing Darwin and adopting Asian cast-offs. I don't know what culture war they're fighting, but any who put belief in the miracles of Jebu above the realities of nature aren't "fighting" for me.

Anonymous said...

How'd women get roped into "feminism," anyway? Our grandmothers had kids starting early, commonly at 18-22, and were a lot happier than modern women. For one thing, our grandmas weren't strapped with tens of thousands of dollars of student loans to pay off from worthless P.C. college degrees.

Feminism happened at the same time integration did.

If you want one group of women to breed, you have to get another group to do or pay for their housework and childcare, either directly or indirectly.

Anonymous said...

The numbers are certainly daunting on the face of it; but what’s truly problematic here is not that, effectively, the human ecology of the northern hemisphere is changing; what’s more troubling is that we (meaning Northern Europeans) are utterly paralyzed in adapting personally and socially to these changes. and far from blaming “the liberals” the problem is more with ideological perspective of conservatives, who’ve clung to an outmoded model of collective decision-making that is long gone--if it ever existed in the first place.

What I’m speaking of here is that the perspective of conservative debate still takes place form the bird’s eye view of what we should all do, as a singular, monolithic culture. This presumes that there is such a monolith of culture that can be turned en masse by simply controlling some mythic center of communication that could be captured and simply switched from broadcasting the poisonous, self-destructive message of the other, and which could possibly be made to belong to us.

Again, this presumes that such a center exists. But it also presumes that the issues of “the decline in white fertility” or “mass third world migration” are secular and superficial--in that they are caused simply by certain messages being incidentally repeated in the media--and have no deeper, structural antecedents. And that, furthermore, these antecedents have not become internalized to a degree that, even if they were to be eliminated, change would be slow--too slow--in coming to make any kind of difference in the demography-as-destiny of the western world.

It is in this way that a debate that should be conducted in the realm of concrete, personal actions gets transposed into a fantasy land of “what things would be like if I were king” where one can, ultimately, wash one’s hands of any responsibility.

Ronduck said...

"Protestants did this?"

As I said, they certainly helped, and are far more culpable than most. I don't think it's a point of debate here at Steve's blog
.

It is a point of debate for me. I brought up Ted Kennedy because I think the Catholic church is culpable in this mess. Right now Catholic hospitals in Massachusetts are preparing to offer abortions. Second Ted Kennedy has promoted a lot of this crap, and he has never been excommunicated for it.

Mark said...

"Read something over the weekend that this reminded me of. The oldest man in the world died in Japan Friday at 113.

He had 8 children. Those 8 children had 25 children. Those 25 children had 52 children. Those 52 have had... 6 children. Really illustrated both the falling birth rates and the slowing of the generational cycle in Japan."

Compare this guy's family with that of Ms. Elma Wickey, an Amish woman who recently died in Indiana at 91.

She also had 8 children. But her 8 children gave her 75 grandchildren. And her 75 grandchildren have given her, to date, 447 great-grandchildren. Though the vast majority of her great-grandchildren are under 20, the ones who aren't have given her, to date, 38 great-great-grandchildren.

http://www.decaturdailydemocrat.com/content/view/165401/32/1/1/

Imagine dying with over 500 direct descendants.