There’s good reason to believe the fertility transition as a general phenomenon is subject to negative feedback, thus almost certain to be self correcting. Selection self-evidently favours high fertility culture and genes.
See this study for an attempt to model the effects:
Correlations in fertility across generations: can low fertility persist? Martin Kolk, Daniel Cownden and Magnus Enquist Published:22 March 2014
″… Our models suggest a mechanism in which the recent fertility decline may be reversed in the long run. Intergenerational fertility correlations create cultural and genetic selection processes that favour lifestyles with higher fertility. Only through continuous cultural change, introducing novel lifestyles associated with reduced child-bearing, can low fertility persist.”
An example in favour of this model is France. France is generally regarded as a low-fertility pioneer, but today has the highest TFR in Western Europe.
It’s still worth paying attention to policy, but worth noting the strong undercurrents at play which are likely somewhat independent of govt tweaking. I think genetics are likely a more relevant factor than has been mentioned in this thread so far.
So other than the sheer resource model I mention—where a declining population frees up job slots and housing and education slots—cultural and genetic selection.
Would this possibly explain countries with extreme long term decline, like Japan? Japan seems to have closer to a true cultural/genetic monoculture, where there may simply not be enough diverse subgroups for ones with the right (cultural and genetic) alleles.
The trend started going back down again, but I think short term trends are unreliable especially with the economic upheaval from the past few years; we’ll have to see if it continues in the longer term.
Imo Japan is one of the more illuminating examples on this topic:
Japan had a TFR of 5 in the 1930s. It’s been only 3 generations since Japan’s TFR began to fall, and France took 5 to stablise around the current level (1830s-1980s). I agree that the trend since 2005 is too short term to be sure, but it’s interesting to note! The above modelling suggests that a faster fertility transition should result in a faster bounceback—the lower the TFR the more adaptive high-TFR genes + cultures will be relatively.
The fertility transition hit East Asia harder and faster than it did Europe. There’s merit to the theory that it’s because Europe had a slower transition to today’s mainstream fertility-surpressing universal culture (technological advancement, enlightenment values. women’s lib etc), since much of these cultural changes were developed in the West (consider the analogy to megafauna in Africa).
It’s extremely difficult to quantify this sort of thing but it does support a model where both genes and culture are load-bearing inputs to TFR. In countries where culture propped up fertility one way or another there could be said to be a cultural fertility overhang, and when these forces were removed TFR naturally cratered in the short term. Where countries had less cultural overhang, or a slower transition from high-TFR culture to low-TFR culture, the transition was less dramatic because there was time for cultural counter-developments or genetic selection to act.
The example of Sth Korea (TFR >5 until the 60s) supports some of these theories. The timing is especially interesting—the 60s were a major leap forward in progressive cultural hegemony, and Sth Korea (an extremely poor society prior) copped that right in the face after the Korean War. The idea is that the speed of TFR-decline is related to the severity of cultural change—makes sense to me.
An optimistic Sth Korean pro-natalist could interpret this current ultra-low TFR period as evidence of an extremely effective ‘weeding’ process which is sure to be followed by a period of high fertility preferences as the most enthusiastic ‘breeders’ will be all that remain!
Note: When I refer to culture above I take the expansive definition which includes technology, wealth, social changes—ie. anything that isn’t genetic.
@Gerald Monroe On the question of Japan’s unique lack of variation, I think it’s unlikely to be decisive here. The ‘monoculture’ argument may have some merit, but even a genetically ‘homogenous’ population has plenty of variation—especially one 125m strong like the Japanese.
Fertility related traits are just so fundamental to genetic fitness that selection is guaranteed to wring out the higher fertility alleles where the environment allows.
I agree, but in a less diverse environment the necessary genes might be rarer/there might be less choices for recombinations. I agree that if there are subgroups in Japan’s populations that under the current conditions are breeding above replacement, and if somehow Japan’s conditions stayed static for centuries, eventually their ‘problem’ would self correct.
Ultimately it doesn’t matter because the conditions are likely to change rapidly in the next ~5-50 years. (leaving a wide window for the event “AGI + follow up developments”)
I mean even ignoring broader scale changes from AGI, the “salaryman working to death” model doesn’t make any sense when those kind of somewhat rote tasks can all be automated.
There’s good reason to believe the fertility transition as a general phenomenon is subject to negative feedback, thus almost certain to be self correcting. Selection self-evidently favours high fertility culture and genes.
See this study for an attempt to model the effects:
Correlations in fertility across generations: can low fertility persist?
Martin Kolk, Daniel Cownden and Magnus Enquist
Published:22 March 2014
https://royalsocietypublishing.org/doi/10.1098/rspb.2013.2561#d3e788,
″… Our models suggest a mechanism in which the recent fertility decline may be reversed in the long run. Intergenerational fertility correlations create cultural and genetic selection processes that favour lifestyles with higher fertility. Only through continuous cultural change, introducing novel lifestyles associated with reduced child-bearing, can low fertility persist.”
An example in favour of this model is France. France is generally regarded as a low-fertility pioneer, but today has the highest TFR in Western Europe.
It’s still worth paying attention to policy, but worth noting the strong undercurrents at play which are likely somewhat independent of govt tweaking. I think genetics are likely a more relevant factor than has been mentioned in this thread so far.
So other than the sheer resource model I mention—where a declining population frees up job slots and housing and education slots—cultural and genetic selection.
Would this possibly explain countries with extreme long term decline, like Japan? Japan seems to have closer to a true cultural/genetic monoculture, where there may simply not be enough diverse subgroups for ones with the right (cultural and genetic) alleles.
Japanese TFR actually has had a bit of a reversal since 2005: https://data.worldbank.org/indicator/SP.DYN.TFRT.IN?end=2020&locations=JP&start=1960&view=chart
The trend started going back down again, but I think short term trends are unreliable especially with the economic upheaval from the past few years; we’ll have to see if it continues in the longer term.
Imo Japan is one of the more illuminating examples on this topic:
Japan had a TFR of 5 in the 1930s. It’s been only 3 generations since Japan’s TFR began to fall, and France took 5 to stablise around the current level (1830s-1980s). I agree that the trend since 2005 is too short term to be sure, but it’s interesting to note! The above modelling suggests that a faster fertility transition should result in a faster bounceback—the lower the TFR the more adaptive high-TFR genes + cultures will be relatively.
The fertility transition hit East Asia harder and faster than it did Europe. There’s merit to the theory that it’s because Europe had a slower transition to today’s mainstream fertility-surpressing universal culture (technological advancement, enlightenment values. women’s lib etc), since much of these cultural changes were developed in the West (consider the analogy to megafauna in Africa).
It’s extremely difficult to quantify this sort of thing but it does support a model where both genes and culture are load-bearing inputs to TFR. In countries where culture propped up fertility one way or another there could be said to be a cultural fertility overhang, and when these forces were removed TFR naturally cratered in the short term. Where countries had less cultural overhang, or a slower transition from high-TFR culture to low-TFR culture, the transition was less dramatic because there was time for cultural counter-developments or genetic selection to act.
The example of Sth Korea (TFR >5 until the 60s) supports some of these theories. The timing is especially interesting—the 60s were a major leap forward in progressive cultural hegemony, and Sth Korea (an extremely poor society prior) copped that right in the face after the Korean War. The idea is that the speed of TFR-decline is related to the severity of cultural change—makes sense to me.
An optimistic Sth Korean pro-natalist could interpret this current ultra-low TFR period as evidence of an extremely effective ‘weeding’ process which is sure to be followed by a period of high fertility preferences as the most enthusiastic ‘breeders’ will be all that remain!
Note: When I refer to culture above I take the expansive definition which includes technology, wealth, social changes—ie. anything that isn’t genetic.
@Gerald Monroe On the question of Japan’s unique lack of variation, I think it’s unlikely to be decisive here. The ‘monoculture’ argument may have some merit, but even a genetically ‘homogenous’ population has plenty of variation—especially one 125m strong like the Japanese.
Fertility related traits are just so fundamental to genetic fitness that selection is guaranteed to wring out the higher fertility alleles where the environment allows.
I agree, but in a less diverse environment the necessary genes might be rarer/there might be less choices for recombinations. I agree that if there are subgroups in Japan’s populations that under the current conditions are breeding above replacement, and if somehow Japan’s conditions stayed static for centuries, eventually their ‘problem’ would self correct.
Ultimately it doesn’t matter because the conditions are likely to change rapidly in the next ~5-50 years. (leaving a wide window for the event “AGI + follow up developments”)
I mean even ignoring broader scale changes from AGI, the “salaryman working to death” model doesn’t make any sense when those kind of somewhat rote tasks can all be automated.