Summary: the number of children people are having is declining, and if we project this out for several centuries we see massive worldwide depopulation. Eventually, the population is small enough that it could get wiped out by a disaster, and most people whoāll ever live are in the past.
I find this unconvincing for several reasons:
Theyāre projecting a very recent phenomenon, below-replacement fertility, to last many times longer than it has so far, instead of reverting to the historical pattern.
A lot of the constraints on family size come down to cost, especially cost of housing/āland, and in a depopulating world housing and land would be much cheaper.
Cheap and effective birth control is very new. Historically, explicit desire for offspring didnāt matter very much: strong desire to mate was sufficient. Humanity is probably already in the process of evolving a stronger direct desire to reproduce, replacing the indirect desire. Maybe evolution is too slow (I doubt it: thereās probably a lot of variety among humans here) but Iād expect to at least see the article mention this objection?
As Michael says in his comment, technological change could easily have huge effects on the parental experience, changing his many kids people want to have.
[Disclaimer: I work at the Population Wellbeing Initiative with Mike and Dean].
As quick responses to those bullets based on my own views of this issue:
Itās true that low fertility is recent, but so is wealth and the opportunities that come with that. The main crux Iām left with is that (1) [save for Israel] there is no economically developed country that has fertility high enough to replace itself and (2) there has never been sustained depopulation via low fertility. Something is going to have to give! My money is on a non-insignificant period of depopulation.
I disagree with this point about financial costs. The cross-section and time-series evidence that richer places and times have fewer children is too hard to square with that claim, in my opinion. Iād be interested to hear if you had a further thought about why that evidence is misleading. (The opportunity costs are high, but as long as we maintain a world with good work and life opportunities for parents, I donāt see obvious reasons why this will fall).
Iād guess what they say about āHeritabilityā on pages 14-15 might be what youāre interested in (i.e., selection pressure for sub-groups that have direct desires for children). I count myself as worried if thatās the force weāre relying on though given the universality of low fertility. (Evolution through new genetic mutations is almost certainly going to be too slow; I think Table 1 indicates births will fall to very low levels in ~300 years with European levels of fertility).
Fair enough! I donāt really know what technologies are in our future with respect to childbearing and parenting. For what itās worth though, even if there were a (costless) artificial womb so good that it was just a button that when pressed produced a baby, most people I know who donāt have kids wouldnāt press the button. Obviously, thatās not the only tech that could change the parenting experience. But it is the most common one thatās proposed and Iām just not convinced it would move the needle much on fertility. Robo-nannies or something that made a serious dent in the time parents felt they should spend with their kids seems like a more important margin to me.
I wrote up a draft post, focusing on heritability; any thoughts before I publish it? Iām especially curious why you think evolution is too slowāif thereās already significant variation within humanity, and weāre in a new period than started recently with birth control + sex ed + lower taboos, it seems to me like it could be just a few generations before people with genetically higher desires for having their own children are having a large fraction of the kids?
My money is on a non-insignificant period of depopulation.
Iād bet on that tooāI just think itās way less than 300y, and we only see modest drops before reversal.
I disagree with this point about financial costs. The cross-section and time-series evidence that richer places and times have fewer children is too hard to square with that claim, in my opinion.
I think my point on housing was wrongāin places with declining populations a more typical pattern is probably that less desirable areas, with the least economic opportunity, depopulating faster. So thereās still expensive housing in places where you can get good jobs, and prospective parents still face large costs if they choose to have kids.
most people I know who donāt have kids wouldnāt press the button
But (a) your non-parent friends may not be the marginal parent and (b) some people would probably now press the button dozens of times.
Robo-nannies or something that made a serious dent in the time parents felt they should spend with their kids seems like a more important margin to me.
My impression is this as well, but more as a cost issue and not a time issue. Childcare is very expensive (itās our familyās largest expense, with three kids), and automation might be able to help with that? Not sure.
Greatāglad you wrote that post up on intergenerational dynamics (and remarkably quickly!). I havenāt read through the details in a while, but I think the best paper Iāve seen trying to estimate heritability at the family-level is this one by Tom Vogl, which you might find interesting to dig into. I believe his headline finding is that in low fertility settings that this composition effect accounts for fertility rates being ~4% higher in this generation than it would otherwise be (but thatās just a refresher from my quick skim just now).
My skepticism about evolution is skepticism about the existing variance in biological preferences for children. Obviously thatās not something we can easily get at, since outcomes are the product of environment + constraints + culture + preferences, etc. But (1) this preference isnāt currently common enough to push some economically developed countries above replacement rate and (2) once social/āeconomic conditions that generate low-fertility stabilize, this sort of mental-model would always predict increasing fertility rates (since every generations composition becomes more favorable to high-fertility). Iām not sure thereās even a single country with moderate to low fertility thatās seen an increase over the last 10-20 years, even though the demographic transition occurred in some countries a few generations ago. (And we only have a few more, ~7-10, generations worth of time until weāre at pretty low population levels).
Though Iām happy to admit that this is hard to generate convincing evidence on, so maybe in a few more generations it could start to show up in aggregate numbers. But until thereās a country or two with consistent increases in fertility, through policy or evolution or whatever, I will remain very concerned that the decline will not be self-correcting.
Donāt have much to add on the other points you made :)
Summary: the number of children people are having is declining, and if we project this out for several centuries we see massive worldwide depopulation. Eventually, the population is small enough that it could get wiped out by a disaster, and most people whoāll ever live are in the past.
I find this unconvincing for several reasons:
Theyāre projecting a very recent phenomenon, below-replacement fertility, to last many times longer than it has so far, instead of reverting to the historical pattern.
A lot of the constraints on family size come down to cost, especially cost of housing/āland, and in a depopulating world housing and land would be much cheaper.Cheap and effective birth control is very new. Historically, explicit desire for offspring didnāt matter very much: strong desire to mate was sufficient. Humanity is probably already in the process of evolving a stronger direct desire to reproduce, replacing the indirect desire. Maybe evolution is too slow (I doubt it: thereās probably a lot of variety among humans here) but Iād expect to at least see the article mention this objection?
As Michael says in his comment, technological change could easily have huge effects on the parental experience, changing his many kids people want to have.
[Disclaimer: I work at the Population Wellbeing Initiative with Mike and Dean].
As quick responses to those bullets based on my own views of this issue:
Itās true that low fertility is recent, but so is wealth and the opportunities that come with that. The main crux Iām left with is that (1) [save for Israel] there is no economically developed country that has fertility high enough to replace itself and (2) there has never been sustained depopulation via low fertility. Something is going to have to give! My money is on a non-insignificant period of depopulation.
I disagree with this point about financial costs. The cross-section and time-series evidence that richer places and times have fewer children is too hard to square with that claim, in my opinion. Iād be interested to hear if you had a further thought about why that evidence is misleading. (The opportunity costs are high, but as long as we maintain a world with good work and life opportunities for parents, I donāt see obvious reasons why this will fall).
Iād guess what they say about āHeritabilityā on pages 14-15 might be what youāre interested in (i.e., selection pressure for sub-groups that have direct desires for children). I count myself as worried if thatās the force weāre relying on though given the universality of low fertility. (Evolution through new genetic mutations is almost certainly going to be too slow; I think Table 1 indicates births will fall to very low levels in ~300 years with European levels of fertility).
Fair enough! I donāt really know what technologies are in our future with respect to childbearing and parenting. For what itās worth though, even if there were a (costless) artificial womb so good that it was just a button that when pressed produced a baby, most people I know who donāt have kids wouldnāt press the button. Obviously, thatās not the only tech that could change the parenting experience. But it is the most common one thatās proposed and Iām just not convinced it would move the needle much on fertility. Robo-nannies or something that made a serious dent in the time parents felt they should spend with their kids seems like a more important margin to me.
Thanks!
I wrote up a draft post, focusing on heritability; any thoughts before I publish it? Iām especially curious why you think evolution is too slowāif thereās already significant variation within humanity, and weāre in a new period than started recently with birth control + sex ed + lower taboos, it seems to me like it could be just a few generations before people with genetically higher desires for having their own children are having a large fraction of the kids?
Iād bet on that tooāI just think itās way less than 300y, and we only see modest drops before reversal.
I think my point on housing was wrongāin places with declining populations a more typical pattern is probably that less desirable areas, with the least economic opportunity, depopulating faster. So thereās still expensive housing in places where you can get good jobs, and prospective parents still face large costs if they choose to have kids.
But (a) your non-parent friends may not be the marginal parent and (b) some people would probably now press the button dozens of times.
My impression is this as well, but more as a cost issue and not a time issue. Childcare is very expensive (itās our familyās largest expense, with three kids), and automation might be able to help with that? Not sure.
Greatāglad you wrote that post up on intergenerational dynamics (and remarkably quickly!). I havenāt read through the details in a while, but I think the best paper Iāve seen trying to estimate heritability at the family-level is this one by Tom Vogl, which you might find interesting to dig into. I believe his headline finding is that in low fertility settings that this composition effect accounts for fertility rates being ~4% higher in this generation than it would otherwise be (but thatās just a refresher from my quick skim just now).
My skepticism about evolution is skepticism about the existing variance in biological preferences for children. Obviously thatās not something we can easily get at, since outcomes are the product of environment + constraints + culture + preferences, etc. But (1) this preference isnāt currently common enough to push some economically developed countries above replacement rate and (2) once social/āeconomic conditions that generate low-fertility stabilize, this sort of mental-model would always predict increasing fertility rates (since every generations composition becomes more favorable to high-fertility). Iām not sure thereās even a single country with moderate to low fertility thatās seen an increase over the last 10-20 years, even though the demographic transition occurred in some countries a few generations ago. (And we only have a few more, ~7-10, generations worth of time until weāre at pretty low population levels).
Though Iām happy to admit that this is hard to generate convincing evidence on, so maybe in a few more generations it could start to show up in aggregate numbers. But until thereās a country or two with consistent increases in fertility, through policy or evolution or whatever, I will remain very concerned that the decline will not be self-correcting.
Donāt have much to add on the other points you made :)
Thanks! Published the post.