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The heritability of fertility makes world population stabilization unlikely

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Re: The heritability of fertility makes world population stabilization unlikely

#71

Post by [deleted] »

ema wrote: post #45
barry-cotter wrote: post #30

Earlier quoted context omitted.

> 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 chang…

I agree, however this doesn't necessarily mean that average fertility will rise again. The environment could keep changing faster than the genes can adapt. Also "desire to have children" might be difficult to encode in DNA so genetic adaptation to the availability of contraceptives might be really slow.

[deleted]

Re: The heritability of fertility makes world population stabilization unlikely

#73

Post by pharke »

barry-cotter wrote: post #66
bin0 wrote: post #63

Earlier quoted context omitted.

> Large families do not just happen due to poverty You're right, they happen due to culture. However, the cultures you listed are notably insular and traditional, meaning they do not have large families for the same reason much of the world does (high infant mortality). I doubt these will ever change, but it is very possible the rest of the world will.

Though I’m sure the Mormons would cop to traditionalism calling a religion where the median man spent two years of his life in a foreign country insular is slightly odd, considering most Americans never leave their own country. Even aside from that cosmopolitanism Mormons have been state governors and been contenders for the presidency. Insular they are not.

Insular was probably the wrong term to use, culturally rigid or conservative might be better. The point is they maintain a high fidelity to the cultural and behavioural patterns of their group. One of which is to eschew birth control and purposefully create large families.

Re: The heritability of fertility makes world population stabilization unlikely

#74

Post by bin0 »

barry-cotter wrote: post #68
bin0 wrote: post #64

Earlier quoted context omitted.

I think there was such a selection pressure when we were nomadic hunter-gatherers. Agriculture is a very recent development anthropologically, so we were still in the mode of one-kid-per-pregnancy, though multiple might have been advantageous. It's possible we developed higher fertility due to that, but we didn't have enough time for that new pressure to kick in.

It’s been 5,000 years since the dawn of agriculture. If multiple births were fertility increasing they’d be, if not normal, at least common in some groups. You don’t even get 1 in 3. Single births are clearly not being found wanting by the Blind Idiot God.

Not necessarily. Mortality of mothers is higher in multiple births; maybe that's a counter-pressure (fewer children). Children do worse as well ([0], [1], [2]). Ladies are not built to carry more than one child, especially considering the size of our children, and agriculture has been such a blip on the evolutionary/anthropological timescale that we have not had time to evolve so significantly as to change our basic reproduction.

[0]: https://watermark.silverchair.com/151663.pdf?token=AQECAHi20...

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5541191/

[2] https://bmjopen.bmj.com/content/4/4/e004514

Re: The heritability of fertility makes world population stabilization unlikely

#75

Post by wcoenen »

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…

But your anecdote is exactly what is explained in the article: the new environment (such as contraceptives) which lead to your ancestors having less kids, will cause increased selection on fertility traits in the future. This will reverse the trend of decreased fertility.

Traits that will be selected: a desire to have more kids, physiological changes that cause resistance against contraceptives, tendency to have twins, etc.

Re: The heritability of fertility makes world population stabilization unlikely

#76

Post by rjsw »

bhouston wrote: post #31

The main factors currently in determining family size is not genetically heritable, but cultural. Culture appears to be heritable but that is just because culture tends to be passed down. Culture can change fast in either way, towards more children or less. This does not mean we will be stable but rather culture matters. For example soon as a member leaves a conservative religion stream and shifts to a more liberal s…

I suspect the infamous variations in average IQ seen in different groups are caused by cultural factors too.

Re: The heritability of fertility makes world population stabilization unlikely

#77

Post by aluren »

_liww wrote: post #52
aluren wrote: post #43

Earlier quoted context omitted.

A lot of people love to chime in about "genetics" or "heritability" despite having no background in actual genetics (no, evopsych or behavioral "genetics" don't count) and publish in low-impact factor journals that are virtually unknown in the actual genetics community (or derided as a joke, like plos one). I'm not sure what to make of this paper to be honest.

What you should understand is: most geneticists wouldn't have had the balls to write this even though it's obvious to them. Someone did have the courage to write it. Now wrap your head around what they wrote.

It's not "obvious" at all and I've never heard anyone in the community express such sentiments, even in more informal settings. I don't even know what "courage" you're referring to. The courage to be associated to a journal with an IF < 4, maybe?

Re: The heritability of fertility makes world population stabilization unlikely

#78

Post by toasterlovin »

Al-Khwarizmi wrote: post #16
barry-cotter wrote: post #13

Earlier quoted context omitted.

Population didn’t stabilise, anywhere, ever. Nothing “worked” for Europe. Most of Eastern Europe is losing population to emigration. If you look at breeding populations rather than geographies you see some populations growing and others shrinking. You don’t see steady states. The population behaviour of the British and that of descendants of those resident in Britain in 1900 are not the same thing. Focusing on nation…

Sorry, I didn't make the best choice of words. With "stabilized" I really meant "stopped growing". And indeed, in practice this has resulted into shrinking, not a steady state.

Fertility rates declining for several generations is not stabilization. It’s a bump in the road while humanity evolves resistance to whatever it is about modernity that causes us to have fewer children.

Re: The heritability of fertility makes world population stabilization unlikely

#79

Post by toasterlovin »

ForHackernews wrote: post #10

I'm sceptical of this result. Most previous research suggests that in countries where immigrants are able to assimilate, second-generation fertility levels converge with local social norms: https://paa2008.princeton.edu/papers/80042

Those immigrants haven’t started the evolutionary process in question, since they have, by definition, only been exposed to a modern developed economy for one or two generations.

Re: The heritability of fertility makes world population stabilization unlikely

#80

Post by novalis78 »

wcoenen wrote: post #75
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…

But your anecdote is exactly what is explained in the article: the new environment (such as contraceptives) which lead to your ancestors having less kids, will cause increased selection on fertility traits in the future. This will reverse the trend of decreased fertility. Traits that will be selected: a desire to have more kids, physiological changes that cause resistance against contraceptives, tendency to have twin…

That makes sense from an evolutionary/ biological perspective- it’s like contraceptives appear to nature like a filter - a global pandemic, an extinction event of sorts. So those who nevertheless have more children - ipso facto- pass down their trait of having larger families despite the availability of a baby pill. Fascinating hypothesis. My next question would be if there is a biological link to religion and fertility.
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