18 ms·
The heritability of fertility makes world population stabilization unlikely
- marliechiller 7y agoadmittedly i havent read the whole article, only the abstract, but: assuming that children from larger families will partially inherit the trait for having larger families themselves seems like a leap to me - arent family sizes in less developed societies generally considered to be either due to religious superstition or because more children = more workers to provide for the family a la victorian times? Once these factors diminish as a society develops, I would argue (from a position of ignorance) that the "traits" governing a bigger family (fertility) are environmental rather than genetic.
- Shnooper 7y agoI agree it's social. In more conservative countries girls receive an unambiguous encouragement to be wives and mothers first.
- saagarjha 7y agoI found this very strange as well, so I skipped down to the section that discussed this: > In countries that have undergone the demographic transition, twin, adoption and family studies have pointed to a substantial genetic effect on fertility (Fisher, 1930; Kirk et al., 2001; Kohler, Rodgers, & Christensen, 1999; Murphy, 1999; Murphy & Knudsen, 2002; Rodgers, Hughes, et al., 2001a; Rodgers, Kohler, et al., 2001b). For example, Fisher (Fisher, 1930) found that a woman could expect 0.21 additional children for each additional child that her mother had, and 0.11 additional children for each additional child that her grandmother had. From this, Fisher suggested that the heritability of fertility at that time was 0.4 (40% of the variation in fertility is explained by genetic factors). Summarising research conducted through to 1999, Murphy (Murphy, 1999) noted that the heritability of fertility averaged around 0.2 in post-demographic transition societies, with the estimates increasing in recent periods. Kohler et al. (Kohler et al., 1999) examined data on Danish twins born in the periods 1870 to 1910 and 1953 to 1964. The first period covers the demographic transition and the second the end of the baby boom. In the first cohort, the heritability of fertility in women varied from close to zero in the pre-transition period to as high as 0.4 to 0.5 during the demographic transition. Estimates of heritability remained strong for the 1953 to 1964 cohort. From an analysis of data for Danish twins from the 1950s, Rodgers et al. (Rodgers, Kohler, et al., 2001b), attributed slightly more than one quarter of the variation in fertility to genetic factors. Rodgers and Doubty (Rodgers & Doughty, 2000) found a median heritability of 0.33 in a contemporary United States population, and heritabilities for underlying desires, ideals and expectations ranging between 0.24 and 0.76. Where measured, the variance attributable to shared environment in low-fertility populations was generally lower than the genetic effects (Kirk et al., 2001; Kohler et al., 1999; Kohler, Rodgers, Miller, Skytthe, & Christensen, 2006; Zietsch, Kuja-Halkola, Walum, & Verweij, 2014). However, the relative balance of genetic and shared environmental factors can change quickly over time (Kohler et al., 1999; Kohler et al., 2006).
- toyg 7y agoThat is still looking at pre-1970s populations, where the female workforce even in advanced countries was much smaller than today and the religious element was still largely hegemonic.
- saagarjha 7y agoYeah, I'm not sure that this data is completely relevant, especially given that the birth rate in the US has gone down something like 25% since 1970.
- danieltillett 7y agoIn this case it doesn't matter if fertility is genetic or environmental. Parents can pass on the trait either socially or genetically, or as almost is certainly the case as a combination of the two.
- sadris 7y agoIn almost every case, parents do not pass traits socially. Shared environment impact is roughly zero in nearly every trait ever examined.
- deleted 7y ago[deleted]
- lalaland1125 7y agoKeep in mind that religion is heritable to a certain degree in that parents usually educate their children in their own religion (bring them to church with them, etc). Sure, it might not be as strongly heritable as a genetic trait, but you can certainly see it.
- andybak 7y agoCould 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.
- mxfh 7y agoSo 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 origin. Women of Southeast Asian descent deviate from the fertility pattern of their parents, while those of Turkish descent preserve their parents’ cultural heritage. These different paths of adaptation between groups partly reflect cultural distance between parents’ country and host country. They also depend on family social capital, family structure, and family values. Access to a higher level of education is a crucial factor in erasing differences between groups" https://hal.archives-ouvertes.fr/hal-02081758/document https://hal.archives-ouvertes.fr/hal-02081758/document
- acqq 7y agoI 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.
- Al-Khwarizmi 7y agoIf this is true, then how do they explain population stabilization in, e.g., Europe, and other developed areas? Why shouldn't what worked for Europe work for the rest of the world?
- barry-cotter 7y agoPopulation 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 nations obscures that fact.
- Al-Khwarizmi 7y agoSorry, 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.
- toasterlovin 7y agoFertility 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.
- ForHackernews 7y agoI don't think humans are every going to evolve past being a K-selected species.
- toasterlovin 7y agoThey can evolve past having below replacement fertility, though. And then they can evolve to something like 3-4 children per woman while remaining K selected. With 3-4 children per woman, the human population will quickly expand to fill out our ecological niche, just as we have done in the last several hundred years.
- ForHackernews 7y agoI'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 https://paa2008.princeton.edu/papers/80042
- toasterlovin 7y agoThose 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.
- j_wtf_all_taken 7y agoWhich "evolutionary process in question" do you mean? Isn't the point that it is NOT about an evolutionary process?
- toasterlovin 7y agoThe premise of the article is that fertility is heritable, which means an evolutionary process is taking place that will overcome the demographic transition.
- j_wtf_all_taken 7y ago> The premise of the article is that fertility is heritable (...) Actually, that was the conclusion, and is exactly the thing that is being disputed.
- toasterlovin 7y agoThe person I’m responding to is disputing that people in developed economies are evolving to become more fertile by pointing to the fertility rates of recent immigrants, which fall within a couple of generations. I am pointing out that these recent immigrants have not gone through multiple generations of selection for fertility in a developed economy, so the fact that their fertility rates drop upon arrival does not invalidate the hypothesis.
- bad_user 7y agoAll 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 staying home and can afford to have children. Nowadays access to contraceptives is common and in Europe for example it's not feasible to have a lot of children due to costs (property, education, women having to eventually quit their job, etc). Anyway, I think the evolution of poverty is a much greater predictor of population growth than anything else.
- benj111 7y agoYes this seems to miss actual examples of developed countries where fertility is approaching and dropping below replacement rate.
- sampo 7y agoSame 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. Only in an environment where having a large family is not the norm, will they surface and have an effect. Just speculating here.
- colechristensen 7y agoThis 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 population and reproduction rates in humans is really far off. We're not having litters of kittens. 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.
- barry-cotter 7y ago> 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.
- ema 7y agoI 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 7y ago[deleted]
- im3w1l 7y agoThis is the strongest (only?) counterargument I've seen. I don't believe it will happen soon though. Politicians only do something when doing something is less controversial than doing nothing and that's pretty far off.
- LeanderK 7y agoI 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.
- DissidentSci 7y agoThis study (https://www.pnas.org/content/114/5/E727 https://www.pnas.org/content/114/5/E727) measured the speed at which selection against cognitive ability is occuring in the Icelandic population (they measured this genotypically rather than phenotypically). The rate at which it occurs is meaningful on the scale of our lifespans. Same is probably true for fertility rates, but as fertility is being selected for directly (rather than the indirect effect on cognitive ability) it's probably even more rapid. Then this study more directly measured fertility's rate of evolution: https://www.pnas.org/content/115/1/151 https://www.pnas.org/content/115/1/151. They used UK Biobank data (genetic data from 157,807 female and 115,902 male unrelated samples). They found the 'Age at First Birth' is the most strongly selected trait in the British population. So in the future we can look forward to a world filled with teenage mums. That this is not obvious to everyone is just a testiment to how little people understand about evolution.
- j_wtf_all_taken 7y ago> That this is not obvious to everyone is just a testiment to how little people understand about evolution. Exactly because things are not obvious, they need to be explained. As long as you do not explain the things you call obvious, you cannot judge if people do not understand a topic.
- adrianN 7y agoCatastrophic 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.
- 0xd171 7y agoIsn't your reasoning backwards? We know that improvements in living conditions lead to reduced fertility. And climate change will worsen living conditions, not improve them. So if areas with poor living conditions have high fertility now, why would even worse conditions (due to climate change) reduce their fertility? Sure, the outcomes and quality of life of the children will be even worse than it is but I can't see how that will impact rates of reproduction.
- adrianN 7y agoSufficiently bad conditions lead to children starving and women not surviving labor.
- sadris 7y agoIn bad conditions humans breed more. There was a ten year famine in Ethiopia yet there wasn't a single year in which the population actually dropped. People stop breeding when they know their offspring will survive
- bhouston 7y agoThe 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 streams their fertility instantly drops in one generation. Israel's government even models this in their demographics projects as the flow between religious streams of Judaism is the biggest fertility modifier in that country. This does means in part conservatives will inherit the earth because liberal culture right now cause smaller families but this is culture. I think liberals have to fix this. Also if a women gets an education her fertility drops and the more education the lower the fertility. This means uneducated women (for whatever reason, religious or other) will inherit the earth. If educated women tend to be those with more genetic talents, and in aggregate this may be the case, then this is quite a problematic trend long term. I think the trends to who has fertility and who doesn't isn't great and should be a real topic of conversation. As a society currently we do not deal with this head on.
- rjsw 7y agoI suspect the infamous variations in average IQ seen in different groups are caused by cultural factors too.
- malvosenior 7y agoThe desire to emigrate from your country/culture could very well be genetically heritable. Birth control is very new all things considered, I don't think it's obvious that the lack of desire to reproduce is purely cultural. It's just too new of an option to see the long term impact clearly.
- j_wtf_all_taken 7y ago>> Also if a women gets an education her fertility drops and the more education the lower the fertility. This means uneducated women (for whatever reason, religious or other) will inherit the earth. If educated women tend to be those with more genetic talents, and in aggregate this may be the case, then this is quite a problematic trend long term. So is there any reason to believe that last "if" is true? Why would that be a problem anyway, as we can simply make sure schools are in good shape to educate those children, no matter the education level of their parents?
- j_wtf_all_taken 7y agoThe authors seem to have a background in economics, does that really fit the research topic of that paper?
- j_wtf_all_taken 7y agoOne of the sources: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126821 https://journals.plos.org/plosone/article?id=10.1371/journal... >> This finding implies that individuals with genetic predispositions for an earlier AFB had a reproductive advantage and that natural selection operated not only in historical, but also in contemporary populations. The observed postponement in the AFB across the past century in Europe contrasts with these findings, suggesting an evolutionary override by environmental effects and underscoring that evolutionary predictions in modern human societies are not straight forward. << Yeah, so basically we got a simple model by two economists vs. decades of empirical data? It'd be funny if it wouldn't sound like a scientists version of the "immigrants will have a lot of children and replace us" lie.
- DissidentSci 7y agoBecause that never happened before in human history: https://www.amazon.com/s?k=Who+We+Are+and+How+We+Got+Here&ref=nb_sb_noss https://www.amazon.com/s?k=Who+We+Are+and+How+We+Got+Here&re...
- j_wtf_all_taken 7y agoWhat exactly is your point?
- deleted 7y ago[deleted]
- j_wtf_all_taken 7y agoSorry, my mistake, forget it. I should have read your other comments first before replying.
- Merrill 7y agoIn rural societies, children are productive members of the workforce and the care of the aged depends on having surviving children. This encourages large families. In urban societies, children are expensive to rear and educate until they can become productive, and the care of the aged depends on social institutions. This encourages small families. However, if urban societies socialize the cost of rearing and educating children, then that disincentive will be removed and families may become larger. Ethnic subgroups with strong extended families and religious solidarity tend to have larger families, even in urban settings.
- nobrains 7y agoSome anecdotal data. My father's parents had 8 surviving children. My mother's parents had 8 surviving children. My parents had 4 surviving children. I have 4 children. My siblings have, on average, 3 children, and will probably have 3.5 over time. My cousin's have on average 3.5 children. Grandparents: Asian. Parents: Asian and lived in Middle East half their life. Me and siblings: Living primarily in Middle East.
- lotsofpulp 7y ago"Asian" is too broad to be a useful descriptor of ethnicity or culture.
- temac 7y agoWell, the finite nature of the world makes its population stabilization likely.
- malvosenior 7y agoThere only needs to be enough resources to advance technology enough to enable space colonization.
- PaulHoule 7y agoHow about a counter effect? Many couples today reproduce with the assistance of reproductive technology. This releases selection pressure, so low-fertility genes proliferate.
- deleted 7y ago[deleted]
- deleted 7y ago[deleted]
- dannykwells 7y agoWhat a garbage article. Clearly misses decades of research on the impact of education and poverty and fertility.
- maire 7y agoThis is the opposite of what Hans Rosling says in his book Factfulness. According to Hans Rosling's findings family size is linked to child mortality which is linked to poverty. When mothers see their children die then they want to have more children. When they see their children grow to adulthood then they have fewer children. You can also play with the data yourself on his site https://www.gapminder.org/ https://www.gapminder.org/. He also looked at family size relation to culture and religion and found even in religions that promote large families, family size is still declining. Family size has dropped world wide everywhere except for Africa. There is an unfortunate link between poverty and family size in Africa. The Bill and Melinda Gates foundation is tracking this exact issue. I am not a data scientist, but the heritability of large families seems a difficult thing to pull out of the data when environment plays such a large role. In my personal family history child mortality and religion did play a large role in family size. We all now have small families.
- theotherview 7y agoThis is a 20+ year recollection...but while working on a Masters in Public Health, we learned that the only causal factor that could be linked to both number of children birthed and age at which a woman gives birth to her first child is the education level of the mother. That is, as women in a society have greater access to education, they postpones when they have their first child and in the end have fewer children in their lifetime.
- maire 7y agoYes - Hans also said the same thing although indirectly. His life work was reducing child mortality (under the age of 5.) He discovered that the biggest factor in reducing child mortality was the education level of the mother. It turns out that most child deaths are preventable if the mother understands how to prevent the death. For instance, dehydration due to diarrhea and vomiting can be prevented by sanitation. Also access to vaccines is linked to the education of the mother. It goes without saying that access to birth control also plays a big factor. Melinda Gates tells a story about how she was talking to a group of African women about vaccines and what they really wanted was birth control so they could plan their family. They couldn't use condoms because culturally it implied they had AIDs. This also seems linked to education.
- neffy 7y agoThe Beak of the Finch by Jonathan Weiner describes (extremely well, it´s a great book to read btw.) the evolution of Finch beaks on the Galapagos Islands. There was one particular Finch/beak size that had relatively small families and population growth, and was clearly being outcompeted by other, better adapted Finches. Until there was a severe drought, when that type of beak was able to take advantage of a neglected source of foods, which wasn´t accessible to the other Finches - who were more sucessful, but only when there was abundant easy food. After the resultant die-off this particular Finch subtype dominated of course. A lot of the discussion of evolutionary traits implicitly assumes an adaption to an unchanging environment, but that is very unlikely to be the actual situation, especially as in adapting, the adaption itself can change the larger environment.