The heritability of fertility makes world population stabilization unlikely • Hacker News Board

Re: The heritability of fertility makes world population stabilization unlikely

#21

Post by LeanderK » Fri, Jul 05, 2019, 9:28 AM UTC

I have always wondered whether something like this could be observed.

I wonder, shouldn't this be already observable? I would look not at the median/mean fertility, but on the outliers on the upper end. If the share increases/becomes more expressed in social groups that are not associated with a large number of children otherwise, one should see indicators that the theory is has some thruth.

Also, we are talking about heritability and entire generations. If such trend can be identified, I would expect it to be very small and take time (measured in generations) until it will have a real effect.

Re: The heritability of fertility makes world population stabilization unlikely

#22

Post by barry-cotter » Fri, Jul 05, 2019, 9:31 AM UTC

bad_user wrote: post #14

All of my grandparents come from big families. My grandmother on my father's side comes from a family of 12 children. Yet my grandmother only had 4 children and my father only 2, and now I only have 1. This is an anecdote, but I don't think heritabiliy has anything to do with it. Large families simply happen due to poverty. When poor, you want more children because there's strength in numbers. Plus the women are stay…

If a trait is not strongly selected for but variation exists it will be maintained in the population. See height, hair colour, propensity to gain weight, etc.

Then you change the environment so that the trait is under strong selection. The people living in Scandinavia 3,000 years ago couldn’t digest lactose. Now ethnic Scandinavians who are lactose intolerant are basically nonexistent. It’s at above 99% homozygotes.

Imagine taking a population and killing everyone over 18 under 1.8m and doing this for four generations. Assuming anyone was left after the first generation the fourth generation will be substantially taller than the first.

Desire for children was never under strong selection pressure before because desire to have sex led to children pretty reliably up until the birth of the demographic transition in France in the ~1700s. Now it is under selection pressure, everywhere with reliable access to contraception so the people who like children are going to have more children, and their share of the population will grow.

> Large families simply happen due to poverty. When poor, you want more children because there's strength in numbers. Plus the women are staying home and can afford to have children.

This will be news to the Mormons, Amish, Hutterites and the Hasidim among a number of Orthodox sects of Jews. Large families do not just happen due to poverty. Some people want more children and arrange their lives around that.

Re: The heritability of fertility makes world population stabilization unlikely

#23

Post by joaomacp » Fri, Jul 05, 2019, 9:36 AM UTC

sampo wrote: post #18

bad_user wrote: post #14

All of my grandparents come from big families. My grandmother on my father's side comes from a family of 12 children. Yet my grandmother only had 4 children and my father only 2, and now I only have 1. This is an anecdote, but I don't think heritabiliy has anything to do with it. Large families simply happen due to poverty. When poor, you want more children because there's strength in numbers. Plus the women are stay…

Same trait may have different effects in different environments. In stone age, bad eyesight might have been a severe evolutionary disadvantage. After we invented eyeglasses, bad eyesight has no effect on your survival or number of children. In a culture where large families were normal, perhaps genetic traits that push you towards having a large family were hidden by cultural aspects that made you have a large family…

Actually, wearing eyeglasses is sometimes perceived as unattractive, causing lower chances of offspring.

Re: The heritability of fertility makes world population stabilization unlikely

#24

Post by [deleted] » Fri, Jul 05, 2019, 9:36 AM UTC

bad_user wrote: post #14

All of my grandparents come from big families. My grandmother on my father's side comes from a family of 12 children. Yet my grandmother only had 4 children and my father only 2, and now I only have 1. This is an anecdote, but I don't think heritabiliy has anything to do with it. Large families simply happen due to poverty. When poor, you want more children because there's strength in numbers. Plus the women are stay…

[deleted]

Re: The heritability of fertility makes world population stabilization unlikely

#25

Post by adrianN » Fri, Jul 05, 2019, 9:38 AM UTC

Catastrophic climate change makes it very unlikely that people in the future will breed with similar success as in the past. Especially poor areas that today show high fertility will be hit hardest by changes over the next twenty to fifty years.

Re: The heritability of fertility makes world population stabilization unlikely

#26

Post by acqq » Fri, Jul 05, 2019, 9:41 AM UTC

mxfh wrote: post #11

andybak wrote: post #5

Could someone with more time than me summarize how they reached the conclusion that fertility was heritable? It seems very counter-intuitive unless I'm misunderstanding the precise meaning of "heritable" that enables them to draw this conclusion.

So far the consesus was that migrants from traditonally child rich societies, acclimated already a generation later at local lower levels if prosperitiy and education level was reached as well. So it's the economy and social stability through the state that replaces children as the only "pension and care" provider for retirement. FRANCE: "We show a convergence towards French standards that differs across groups of or…

I suspect that “Southeast Asian” women observed had different religion than those where “fertility pattern of their parents” is preserved.

Not all religions have the same effect on the outcomes, ignoring that in the studies is misleading.

Re: The heritability of fertility makes world population stabilization unlikely

#27

Post by ptah » Fri, Jul 05, 2019, 9:43 AM UTC

bad_user wrote: post #14

All of my grandparents come from big families. My grandmother on my father's side comes from a family of 12 children. Yet my grandmother only had 4 children and my father only 2, and now I only have 1. This is an anecdote, but I don't think heritabiliy has anything to do with it. Large families simply happen due to poverty. When poor, you want more children because there's strength in numbers. Plus the women are stay…

in the old days manual labour was an incentive to have as many hands as possible. also infant mortality was high

Re: The heritability of fertility makes world population stabilization unlikely

#28

Post by pas » Fri, Jul 05, 2019, 9:53 AM UTC

barry-cotter wrote: post #22

bad_user wrote: post #14

All of my grandparents come from big families. My grandmother on my father's side comes from a family of 12 children. Yet my grandmother only had 4 children and my father only 2, and now I only have 1. This is an anecdote, but I don't think heritabiliy has anything to do with it. Large families simply happen due to poverty. When poor, you want more children because there's strength in numbers. Plus the women are stay…

If a trait is not strongly selected for but variation exists it will be maintained in the population. See height, hair colour, propensity to gain weight, etc. Then you change the environment so that the trait is under strong selection. The people living in Scandinavia 3,000 years ago couldn’t digest lactose. Now ethnic Scandinavians who are lactose intolerant are basically nonexistent. It’s at above 99% homozygotes.…

> It’s at above 99% homozygotes.

Meanin 99% of people who have this allele (trait) have two set of the corresponding gene/genes.

Okay, but is lactose tolerance a dominant allele?

Re: The heritability of fertility makes world population stabilization unlikely

#29

Post by car12 » Fri, Jul 05, 2019, 9:59 AM UTC

acqq wrote: post #26

mxfh wrote: post #11

Earlier quoted context omitted.

So far the consesus was that migrants from traditonally child rich societies, acclimated already a generation later at local lower levels if prosperitiy and education level was reached as well. So it's the economy and social stability through the state that replaces children as the only "pension and care" provider for retirement. FRANCE: "We show a convergence towards French standards that differs across groups of or…

I suspect that “Southeast Asian” women observed had different religion than those where “fertility pattern of their parents” is preserved. Not all religions have the same effect on the outcomes, ignoring that in the studies is misleading.

What it is pussyfooting around is that there is not that drastic of a drop in fertility rates of muslims.

I guess it shouldn't be hard to conceive where Islamic parties start having a major voice in elections because of demographics.

Re: The heritability of fertility makes world population stabilization unlikely

#30

Post by barry-cotter » Fri, Jul 05, 2019, 10:07 AM UTC

colechristensen wrote: post #15

This is ridiculous. The replacement fertility rate to maintain population before modern medicine could be closer to ten than two not so long ago. War, famine, disease, accidents, and infant mortality made it so surviving until you were old enough to start having your own children was rare and women were often pregnant or nursing continuously as long as they were fertile. The premise of heritable fertility driving pop…

> The premise of heritable fertility driving population and reproduction rates in humans is really far off.

Yes, until reliably accessible contraception fertility was driven by the desire to have sex.

> If it were true fertility rates could not possibly have dropped so far in so few generations after modern medicine and the insane reduction in violent death rates seen in the last thousand years.

This assumes no change in the environment, when it has manifestly changed. In this new environment in which desire to have children leads to having more children, on average, the desire to have more children will be selected for.