Debunking fertility rate paranoia

A certain type of person loves to obsess over an arbitrary point of “fertility falling below replacement” as if that is the point of no return for population collapse.

The world’s richest man is worried that there aren’t enough humans.

Elon Musk Tweet 1
Elon Musk Tweet 2

So I think I see where the panic comes from. People seem to conflate birth rates falling below fertility with an inevitable population collapse. Once you fall under the replacement rate, a collapse must continue until there are no humans left. Or something like that.

This seems entirely at odds with the reality that there are more human beings alive today than at any point in the history of the universe.

Further, the total number of humans alive today doesn’t really tell us much about the total number of humans that will ever live.

So why the obsession with more humans being alive at the same time rather than over time?

It’s a question I think needs to be asked in these discussions.

There are three main reasons I am not worried about fertility decline.

  1. The experience of countries that saw previous declines
  2. Fertility is probably heritable
  3. Age structure is not that important

Previous fertility declines usually bounce back

Even Elon’s own chart in that first tweet above shows a collapse in fertility in the 1970s and 1980s that then recovered quite substantially. I’m sure plenty of people expressed similar concerns then.

The United State population is now over 100 million larger today that in 1985. Sure, there was a lot of migration. But the fertility recovery contributed too.

It is reasonably common for fertility rates to move in cycles, and even for slight recoveries from the “fertility transition” to occur.

Max Roser Tweet

Is fertility heritable?

It seems likely that fertility is heritable as this paper explains.

Fertility paper

If this is true, we should expect fertility recoveries in many more places. The below charts are the simulations from that paper. The grey lines show the baseline projections and the black lines show the difference that adding some heritability of fertility makes to the projection.

Notice that in Europe, most projections are already for a recovery in the fertility rate over the longer term. Add heritability and you get a more fertile long-term pattern

Global fertility rates

Even the baseline forecasts show world population growing until the end of the century.

Age structure

Lastly, many express concerns that low fertility means an ageing population. The fear is that there will be too many old people for young people to support.

I have a whole report debunking this concern.

Firstly, low population growth is related to higher productivity growth.

Population versus productivity

Indeed, a study by MIT economists found that

…that even when we control for initial GDP per capita, initial demographic composition and differential trends by region, there is no evidence of a negative relationship between aging and GDP per capita; on the contrary, the relationship is significantly positive in many specifications.

Also, ageing doesn’t seem to change the overall participation in the formal workforce.

Population ageing and labour force participation

And lastly, of course, children are dependents too. So those concerned about looking after people who aren’t in the workforce should factor in the fewer dependent children rather than looking at one side of the ledge only.

In sum

Don’t worry so much. Populations change and evolve and that’s fine. Support people to have as many children as they like. But let’s not worry about problems that seem to exist mostly in our imaginations.

Dr Cameron Murray is co-author of the Book Game of Mates. Subscribe to his written work at


  1. kannigetMEMBER

    You missed the whole point, declining fertility rate of the right kind of people will lead to a collapse of the population of the right kind of people…….


    • What a light weight! Ignored that the Roman Empire (and others) fell as a result of several bad pandemics that destroyed their working populations. Clearly doesn’t understand simple math.

      Lefti woke narrative – that we are the disease, and the cure is less of us… self hate means others will replace – and maybe that is why the Chinese (or others) may eventually rule us. Because, they will do something about it.

    • What a fool. I can’t believe DLS ever celebrated with sure a short sited fool. Does he understand the concept of trends. Wonder if he has ever seen Peter Zeihan’s work or saw the population pymarid of south Korea, Germany, Italy, Japan so on. Must understand that all the population rise in the developed world since 1990 is due to rising in older people and not increased births

  2. Fishing72MEMBER

    Elon is worried that without infinite population growth the Earth may not become unliveable to the point that we’ve all got to back his fantasy of relocating human civilisation to Mars.

  3. Ronin8317MEMBER

    US doesn’t have a problem, but it is a problem for Japan (1.3) and South Korea. (0.83). For Japan, it’s based on two simple facts.

    Average salary of Japanese man or marriable age = 3 million yen
    Average salary expectation a woman has for her husband = 4 million yen +.

    For South Korea, it’s purely because of BTS 😛

      • Soon enough will be no honey even if you have the money. Varroa mate!

        Also, watch for the foot-and-mouth disease. Apparently Bali is crawling with it.

    • Don’t forget to include Taiwan (1.3 from memory) in the same club as S.Korea and Japan.
      The same sentiment is common in China itself and this has nothing to do with China’s 1 child policy, having multiple kids is just not what young Chinese want from their lives.
      I know several young Chinese women (under 40) that have had 1 child and made sure they won’t have any more. They’re very open about it, the 1 child was for their parents, more often then not the child is raised by the grandparents (but that is also a very Chinese thing)

      • Let’s face it, as soon as women have had the chance to control their own fertility they have grabbed hold of it with both hands and won’t let go. It’s just how it is.

        • I’m not sure that I would go there. For me it’s all just a real time experiment in social change.
          We ‘re actively reinventing the society that we want to live in and this new society (like all social groupings before it) demands adherence to its maxims.

          • All populations of every species wax and wane. Very interesting to me what happens on the downside.
   has good graphs on this, but it’s the same dynamic everywhere regardless of race or creed.

    • I think you’ll find that the important question is what is the population density of Japan in comparison with say the US.

  4. blindjusticeMEMBER

    The best proxy for quality of life, for the general population, would be the fertility rate and how many children a couple would want to have versus how many they have. Throw all the ‘most liveable ‘ city indexes in a bin.

    Falling fertility rates are not a problem unless the rate is below replacement AND the incumbent population would like to have a higher rate but cannot afford to AND the population is increasing through other means.

  5. Wilhelm Von WobblecockMEMBER

    Yeah Elon is worried because Japan and South Korea tax inheritance at 50 and 55% respectively for the wealthy, instead of taxing the hell out of workers to pay for the old people. Wouldn’t want that system implemented where he lives!

    • Instead of throwing Elon in a box of billionaire = bad man how about you do someone real reaseach into him. Infact better yet you should invest in tesla and in 10 years when your money has gone up 20 fold you may not be so resentful.
      Of course that would require using the thing between our ears so most people do the easy things and sook instead of real thinking

      • Amazing to me how people who think they are capitalists are actually monarchists desperately looking for a master to be a subject to.
        The heart of capitalism is harshly questioning the wealth of people and if they are worth it.

  6. Jeez, Cam, that’s a pretty lame assessment. The big issue is the shape of the population curve. The reason the global population continued to grow is because we raised billions away from the starvation line and more people are living much longer. Then we stopped having kids at anywhere near the same rate except in a few countries. That older cohort – the pig in the python – will soon pass through. Have a look at Chinese demographics and project forward. Or Italy’s. Or Germany’s. Go read Peter Zeihan’s “The end of the world is just beginning”. It’s clear that 80 years of peace since the 2nd World War has provided a once-off dividend in terms of prosperity and population growth (with the inevitable downside of population growth and pollution).

    IF, as Zeihan predicts, the US largely withdraws from world affairs to concentrate on itself and not policing the world. Nor letting itself be the one paying the privilege of open markets and having the global reserve currency. (Why withdraw? Because it has cheap energy, the best and largest amount of agricultural land plus the cheapest and largest riverine network to move it all about on and more deeper ports than the rest of the world, a huge internal market Canada Mexico, the most liquid and deepest capital market, and no border issues worth worrying about – with the added value of cheap Mexican labour on its doorstep), then that global withdrawal buy the USA spells the end of many complex supply chains currently dependent on unfettered maritime trade (no pirates) and secure borders with globalisation humming at max warp.

    What happens if and when that fails? Not enough fuel or food. “Energy is life” as Doomberg puts it. We’re going renewable? Really? Ask how well that’s going or Sri Lanka? Venezuala? Libya? They’re just for starters. Who has babies when they have no money (in the West)? What does that do to demand…and therefore output…and jobs…and income…and spending?

    Saying that because a woman’s mum and grandma popped out babies therefore it’s all good is facile, That we had babies once so we can do it again? This presupposes that economic conditions encourage women to have MORE babies…and they don’t because the economy is shite and only likely to get a whole lot worse. Ot the fact that sperm counts have been plunging. Your argument is rooted in the past. The simple and obvious conclusion is this: Old people don’t make babies. You can’t print 20-35 year olds. If they don’t exist now in large enough numbers you can’t magic them into being and force them to have babies. No baby boom = no consumption boom. Of course, immigration is a help, but it has major drawbacks. Low-end chain migration that comes to get free school and medicare with loads of grannies in tow doesn’t add much in the way of productive value and burdens the system, at least for a generation or two. Migration is designed to lower wages and increase profits in the short term. It is not structurally designed to increase total productivity and therefore national wealth. You know that. So at least be honest and look at both sides of the situation, instead of claiming it’s all cooler than a Perry Como groupie because…yay, history is going to repeat. It won’t. It can’t. The drivers that enabled it to happen are gone.

  7. In my lifetime, global population has rocketed from 2b to ~ 8b, and it will hit ~ 11-12b before it even begins to stabilise. SCOTUS has just declared open season on US women, whether by gun or by impregnation. Musk himself has seven US kids with disturbing names – just the ones that we know about. At what point would he shut up and stick to driverless EVs?

    • 7.8Bn people, with an additional 81m (births minus deaths) added annually. Global population is forecast to plateau at 9.7bn around 2064. The replacement fertility rate is roughly 2.1 live births per woman for most industrialised countries (the current average globally is ~2.66). With the exception of Israel, no developed nation has a replacement birth-rate. More surprisingly, more than half of the developing world has birth rates around (e.g. India at 2.2) or below (e.g. China at 1.2) replacement levels.

  8. pfh007.comMEMBER

    I am sure all the animals that we have driven to extinction are very amused by humans yapping about how 8 billion resource consumers are simply too few.

    Has there ever been a more self absorbed animal on the planet?

    Truly amazing how the creator of the universe looked just like us!

    What are the odds of that?

  9. Population growth is a core part of economic growth, the fuss is about the fact our economic systems require the growth to function, otherwise they fall into a piling heap. We’ve been using the 3rd world, immigrants and printing to mask the decline in population growth. Problem is those tricks are no longer effective or cannot be done at the scale to help stop the decline.

    So don’t be surprised to see governments change and start pushing people to have more kids soon. The recent drama in the US is pretty much all about that.

  10. Agree, as tar population declines housing will become cheaper & more children will be born. Also in coming decades our advanced technology will be able to more than make up for any shortage of people. And time will be benefits to the environment. Not to mention if the world wants to live the same lifestyle as an Aussie then we have to have falling population.

  11. Leroy Huggins

    What idiotic analysis. Societies which have had birthrates fall below replacement have NOT shown a tendency to be able to lift them back again. Going from a below replacement birthrate, to a higher but still below replacement birthrate is still walking out of existence, not into health.

    Moreover below replacement fertility rates are occurring in a context of other humans (differing culturally, religiously and genetically) being imported, which acts to speed up the rate the population on the receiving end is replaced, disenfranchised and sent out of existence.

    Even if a healthy fertile core were to remain within the receiving population, this would occur thanks to mass immigration in a scenario where that group had been politically & culturally disenfranchised… living as a minority amongst people different to it, and not necessarily in alignment with its needs, desires and views.

    Below replacement fertility is a massive problem for any group on the receiving end of mass migration, an existential threat, directly charting a course to (at the very least), the political dispossession of the receiving population. i.e. their colonisation by people foreign to them, and the turning of their society to serve the foreign group’s needs, not their own. (You know that teaching that Whites are evil is not IN the interests of White people right?).

    • Australia’s Genuine Progress Indicator peaked in 1972 when we had a population of around 15 million. I agree with you about mass migration. According to the 2006 Productivity Report on Immigration, the only winners from it have been the owners of capital and the migrants themselves. Unfortunately, those owners of capital also own the politicians who supposedly represent us.

      If we want replacement level fertility, then we must make our society a lot more family friendly. According to the demographer Joel Kotkin, high density is a more effective way to bring down fertility rates than China’s one child policy.

      We also need to make motherhood less financially risky or punishing to women, perhaps giving mothers some of the benefits that we now give to veterans, since in both cases, individuals are making sacrifices that have benefits to the community. As it is, the fastest growing group of homeless is women over 55. In the past, society could get its reproduction done on the cheap, because women were second-class citizens without many options in life. This is no longer the case.

  12. kiwikarynMEMBER

    It seems that a lot of countries are experiencing a record low number of births in 2022, although you wouldn’t have heard about as the news has been scrubbed from the Internet and Google search results (despite the fact that everyone is talking about it). Funny that. So Taiwan births were down 23% in May (after 7-8.5% drops in March and April). Fortunately, Google hasnt managed to delete official Chinese Govt websites yet so here’s proof that its not a figment of imagination from crazy conspiracy theorists.

    • drsmithyMEMBER

      Doesn’t look like much of a smoking gun in context. It’s a relatively large drop YoY, but the downward trend in births for the last decade (and probably a lot longer) is pretty clear.

      May 2021: births increased 0.53% over May 2020
      May 2020: births decreased 16.12% over May 2019
      May 2019: births decreased 4.53% over May 2018
      May 2018: births decreased 3.11% over May 2017
      May 2017: births decreased 9.09% over May 2016
      May 2016: births increased 6.61% over May 2015
      May 2015: births increased 3.91% over May 2014
      May 2014: births decreased 3.48% over May 2013
      May 2013: births decreased 12.51% over May 2012

  13. This is only a concern for certain generations who still think retirement at 65 is a viable option. For later generations who’ll need to keep working until they drop it’s not really an issue. Allow people a maximum of 5-10 years retirement, they can choose when the clock starts.

  14. MathiasMEMBER

    > It seems likely that fertility is heritable as this paper explains.

    Thats great analysis on human biology and heritability but doesnt take into consideration external factors ( Lack of Food, Oil, Homeless Generations ). So a famine has no impact on fertility rates at all?

    I’d also like to present two charts.

    US Birth Rates –
    US Bond Rates –

    Unless Im mistaken, those two charts look very similiar.

    • MathiasMEMBER

      > Lastly, many express concerns that low fertility means an ageing population. The fear is that there will be too many old people for young people to support.

      Dont know much about low fertility correlating to an ageing population. However, surely a Booming Health Care Sector seems like a pretty good sign.

      Its not just Australia. Health Sectors have been booming in many other countrys as well. The signs are obvious.

      > I have a whole report debunking this concern.
      > Firstly, low population growth is related to higher productivity growth.

      x Countries with older populations maintain high workforce participation
      … Yeah, coz the young people are looking after the old people. ‘Bed pan economy’.
      x Low net immigration of between 50-80,000 permanent migrantsper year can alter the age structure over the long-term by stabilising the population
      … Why is it that Bond Yields are correlated to Birth Rates but dont seem to be overly correlated to Migrant rates all that much? You can clearly see a pattern for Birth rates but despite all the migration we’ve pulled in over the years, it hasnt affected yields much.
      x There is a real economic cost to high population growth due to the diseconomies of scale inherent in rapid infrastructure rpansion
      … I dont think anyones debating that. Things do look different when looked upon in GDP per Capita terms. A good model, imo.
      x Reframe ageing as the economic success story that it is
      … The Social Inequality that exists between the young and boomers, has effectively set the young back 20 years. From 2005 to 2022, we’ve seen massive house price rises that has basically destroyed young lives. Migration has completely wrecked job opportunities. The young have effectively been swimming up a stream as a result of an aging crisis. Granted, a smart government could have implemented a nice plan to sort all this out but that never happened. The only plan was ‘Fear and Denial’, ‘Lies (Avocado and Toast)’ and tonnes of other bullsh-t. There was also many documents that young people where just staying at home and not moving out ( a by-product of this aging crisis and the fact housing was too expensive ). Im pretty sure Im not making this stuff up. Latest census has just seen home ownership rates fall from 40% to 30%. A lot of young people cant grow up because they are deadlocked in a situation of no house, lost job opportunities and crap tonnes of damage. There entire lives have basically been held on ice for 20 years. To look at it another way, there lives have basically been stolen from them. Im pretty sure if you asked most young, they wouldnt call that an Aging Success story. They are p-ssed off ;p

      Your article sounds more like a political argument then an unbiased fact piece. Debating an argument towards a series of values, bringing forward all the positive case scenarios without actually identifying any of the bad realities we’ve seen for the past 20 years. You’ve basically ignored the problems of the past 20 years as if they didnt happen.

      I couldnt care less really whether populations rise or shrink. Doesnt matter to me either way. However, destroying 20 years of life and watching all the social fragmentations starting to form seems pretty real to me.

      In 2019 census, Marriages collapsed by 30% in one of the largest falls we’ve ever seen. If I accept that less population growth is good for society ( better for gdp per capita ), has anyone given any consideration to how this will change Australias Social Future? Singles societys, Hikomori, Loneliness pandemics, Lack of motivations, suicide rates and all the rest? Im pretty sure there’s going to be social implications to all of this.

      My concerns arent really about collapsing populations ( I like peace ) but more the fact we’ve just wiped out 20 years of young life, have a social timebomb we are pretending doesnt exist, health sector relabeled as productivity, homeless crisis because boomers wont give up power and pretty much no future plan for when all this decides to go bad.

    • MathiasMEMBER

      and hopefully Im wrong about this ;p

      Am I to understand that we are going to waste 20 years of peoples lives ( 20 20 = 40 ) and expect 40 year olds to start getting a job and saving for a house?

      Whats wrong with this plan? Oh I know… by 40… they’ve given up and walked away from society ;p

      20 years is a generation and thats a generation thats been wiped out completely. This doesnt sound like a good plan to me.

    • drsmithyMEMBER

      Unless Im mistaken, those two charts look very similiar.

      In that they’ve both got blue lines ?