Jason Collins and Lionel Page write,
The United Nations produces forecasts of fertility and world population every two years. As part of these forecasts, they model fertility levels in post-demographic transition countries as tending toward a long-term mean, leading to forecasts of flat or declining population in these countries. We substitute this assumption of constant long-term fertility with a dynamic model, theoretically founded in evolutionary biology, with heritable fertility. Rather than stabilizing around a long-term level for post-demographic transition countries, fertility tends to increase as children from larger families represent a larger share of the population and partly share their parents’ trait of having more offspring. Our results suggest that world population will grow larger in the future than currently anticipated.
Collins is humble about the ability of any model to project fertility, given the importance of cultural evolution. I have not seen the paper, but I would like to know whether they tested their model against actual data in any way. For example, you could “backcast” the model and see how well it “predicts” population in, say, 1980 or 1950.
Predicting fertility across the nation is a lot the stock market or housing prices in which it is exponential function that change over time horizons of 5 – 10 years. And an exponential function with even .1% error of fertility, which is a modest error, has much much bigger effects over 10 years. (And in terms of population you do have model health care changes as well although developed world is fairly consistent.)
1) In terms of Europe and the far Asia with low rates we have a number of nations that the fertility rates has been going up. (Japan, Sweden, Norway) Long term we don’t know if this will continue or stabilize. (Note in the case of Japan there are still less births today than in the 1980s even with higher fertility rates as the number of women declined.)
2) Who would have predicted India is near or at replacement fertility levels and big over decades. (Remember Camp of Saints assumed they would be the raging Immigrant underclass in the early 1970s.) My guess is fertility flatlines with modest growth but who knows.
3) We are seeing all kinds of claims across Africa where the fertility is ‘dropping’ but still high. It is impossible to model here.
4) The US had very unexpected fall in births in 2017 of ~100,ooo although the drop in US fertility is for mostly the right reasons as single motherhood has dropped to 38%.
At this point, I still think global fertility rates will evidently fall to replacement levels as the more technocratic the world, the less people make emotional decisions and that they can not afford too many children.
The one thing about the Nate Silver statistic nerds is they are making predictions of percentages because you really don’t know the reality. I remember the Patriots/Eagles Super Bowl and I said I believe the Patriots would win 55% of the time and the Eagles were underestimated by most people. (In reality if you read Nate Silver 2016 analysis he did predict Trump had a 30% chance of winning and saw three areas of 2016 polls showing his victory. The polls were herding the results too much, state level polls were not good, and there was 10% chance Trump would win the election but not the popular vote. All three were correct.)
Anyway, my favorite clip about experts being wrong is the Simpsons:
https://www.youtube.com/watch?v=RZJSpVb6uFg
On a long enough timeline maybe high fertility genes outbreed low fertility genes. Of course that assumes a constant environment. In the west I suspect the mechanism that would prompt larger families, the freeing up of resources that smaller families aren’t using, will be short circuited by immigration and old age obligations.
I think the bigger issues is perceptions of what’s normal. If all your friends have one kid, one kid is normal. If you grow up without siblings, that’s the new normal. If childlessness is normal, why have children.
I think its a bit harder to change these perceptions once they are in place.
Isn’t the low birth reality Japan and not the far west? Europe and the US are a generations behind Japan. And in terms of birth rates outside of income levels, the two most predictive variables about a nation fertility rate are Religious Levels of the population and population density. (And really what does Immigration have Significance with higher/lower birth rates? There is some negative effect of population density but higher immigration would lower day care costs and it is often the new immigrants that have higher birth rates than natives.)
Anyway, the reality of the US birth drops from 2008 to today is ~80% for the right reasons which is single motherhood has dropped from 45% in 2007 to 38% today. So again, I believe the more technocratic a society, the less people make emotional decisions.
But not many years ago, four or three kids were normal. The point is that what is normal changed. Obviously, the perceptions of what is normal changed, and changed fairly quickly.
Low fertility has been the new normal across the OECD since the end of the baby boom. While it could in theory change, we haven’t seen much evidence that it actually will.
Look at birth rates and availability of the birth control pill. At least in the US they line up well.
It’s a once-ever change with implications that are still working themselves out.
Actually the big fertility lines up better with abortion rights in the early 1970s across all the rich developed nations.
One aspect of the abortion rights is the Nate Silver might call ‘Issue Opportunity Cost’ in which legal abortion right battles limits the political battles of birth control. (Note in the 1960s there were a lot more cases of birth pill than in later decades.)
So you’re saying it was easy to change perceptions and behaviors at “the end of the baby boom”, but it’s very difficult now. That may well be true.
I think the circumstances of modernity are so different from everything that came before that we can’t assume human beings will be able to adjust to new equilibriums easily, quickly, or while preserving states of affairs most of us would prefer to preserve. The 20th century, for instance, had many examples of not being able to adapt well that we’ve all read about in history books.
We did not evolve to thrive in this environment. We evolved to survive in some malthusian agricultural environment. We may or may not adapt now that we are here, that’s a maybe.
Per Collin, I think we’ve been moving more on the technocratic lines that minimizes correcting mechanisms by building up tail risks and spending down social capital (see Taleb’s anti-fragility).
Low fertility among the high IQ allows us to spend down their intelligence on economic production and not ask difficult social change of them, leading to higher GDP and “stability” now, at the expense of future human capital. It’s very emblematic of the kind of “solutions” our technocratic regime comes up with. We haven’t seen the long run effects yet.
@asdf: “We did not evolve to thrive in this environment.”
True, but if this environment lasts long enough we will eventually evolve to thrive in it. Which is to say that future humans will be much more reproductively efficient than we are in this environment.
Given the magnitude of the behavioral differences observed across families (no kids vs. 4+ kids), the rate of evolution should be rather fast. I’d expect noticeable effects within a few centuries, maybe a few generations.
Like others, I suspect that forecasting fertility rates, especially for developed countries, is extremely difficult. So who knows; maybe some kind of unforeseen technological or social revolution comes along that radically changes the opportunity costs of having children. Even now, the share of women 40-44 who have given birth at the US is apparently at a high level; 86%. So just a few changes which get women giving birth earlier may lead to a relatively rapid increase in the fertility rate. If the economy keeps going like it is, and people can get themselves into jobs with a family supporting wage by age 20 reliably, you might start to see something of a trend towards younger marriages and more kids, as happened once the country rebounded from the Great Depression.
A 2008 working paper and a 2012 published article (La Ferrara, Eliana, Alberto Chong, and Suzanne Duryea. 2012. “Soap Operas and Fertility: Evidence from Brazil.” American Economic Journal: Applied Economics, 4 (4): 1-31. ) has been widely and frequently cited for the proposition that seeing small families on TV encourages poorer women to have fewer children. The abstract states that:
“We estimate the effect of television on fertility in Brazil, where soap operas portray small families. We exploit differences in the timing of entry into different markets of Globo, the main novela producer. Women living in areas covered by Globo have significantly lower fertility. The effect is strongest for women of lower socioeconomic status and in the central and late phases of fertility, consistent with stopping behavior. ”
Bannerjee and Duflo’s book “Poor Economics” discuss this and other random cultural components of fertility.” For example they mention Peru where land reform resulted in women getting their name on property ownership documents. Fertility in women who now had title to property declined sharply.
From this I gather the impression that different factors may influence fertility in different ways in different cultures. This tends to confirm my priors that micro-level analysis is where the larger truths are at and that macro-modeling is likely to be largely descriptive and non-explanatory. People are not fungible.
I wonder if there’s not a bit of long-run game theory here too? To the extent that a given culture’s fertility drops below replacement rate for too long, is there an impetus to promote fertility, and is that effective? (i.e. a given Italian family will make the best decision for itself, all things equal, but will “Italians” be satisfied with the growing prospect of a shrinking culture?)
I don’t know the answer — so purely speculative. (And not intended as xenophobic, although it could certainly be read as such, I suppose.)
Robin Hanson has written a bit about this, and I would recommend anyone interested in this topic start there, and “Fertility Fall Myths” is a decent first step on the path. One stubbornly persistent myth that is quite common is that low fertility is due to lack of resources, but as soon as societies start to become wealthier, then anywhere one looks, one finds that it is always the rich and elites who start having fewer children voluntarily first, and the the poor who have the most. Yes, extreme economic conditions (booms and busts) and the affordability of housing and family formation in general matters on the margin, but it can’t account for the dramatic changes we’ve observed over the past three generations.
The fact is that we do have a few historical examples before ‘modern’ circumstances and chemical contraception (e.g., France from 1750-1800) and we actually know a lot about what is going on, but that the correct analysis of the real state of affairs quickly runs into some socially discouraged truths, and the obvious implications for any state interested in boosting natality tend to upset a lot of people which make them unmentionable in the current climate. If discussions about quantity are already difficult enough, then discussions about quality are altogether taboo.
A reasonable first step approach to discovering explanations is to look for patterns in the detailed data. Do we see big differences with regards to wealth, race, education, status, zip code, etc. It’s common to report data aggregated across entire countries, but it’s the disaggregated data where the strong patterns and correlations are most clear (though, as above, too sensitive to discuss openly).
In general, when women are able to reallocate their efforts away from children and towards status, they tend to choose status, and so having lots of kids starts becomming a signal for low status, which feeds back into the mechanism. Natalist religions which elevate the status of women depending on the number of children they bear tends to mitigate this tendency, as does the perception of social normalcy conveyed by both real experience of the actual number of children typical (and especially high-status women) have, and virtual experience of consuming media and entertainment.
The countries with the highest natality rates tend to be those that are Islamic, poor, and where women marry and procreate early, and are dependent on husbands or fathers, where “immoral influences” media is filtered, and have very little opportunity to independently pursue education or status. The highest status women tend to be family matriarchs. The countries with the lowest rates tend to be secular, rich, and with lots of financially independent, employed, and highly educated females free to choose to seek status over motherhood, and with delayed marriage and childbearing. The highest status women are often single and/or childless.
Now, it is true that to the extent anything in inheritable at all and has superior adaptive fitness in terms of number of descendants, the determinants of that expressed trait will gradually increase in frequency. But if the more fecund group does not otherwise resemble the less fecund group in many important respects, then that (eventually) higher fertility future will look a lot different than the present.
> In general, when women are able to reallocate their efforts away from children and towards status, they tend to choose status, and so having lots of kids starts becomming a signal for low status, which feeds back into the mechanism.
Interestingly, the home school movement seems to be reversing this trend. The ability to form communities around homeschooling, especially when mediated by social media, allows women opportunities to gain status by being mothers. Do you know how much status a woman can have when she posts pictures of 5 beautiful children all playing happily or studying Latin together? 0_o
Furthermore, such communities are creating roles for women whose children have all “left the nest”. It becomes a natural transition from parenting and teaching one’s own kids to helping other parents do the same.
It’s still a relatively small movement, but it seems to be growing pretty rapidly and largely under the radar.
This is a really good summary of things impacting fertility. This is merely anecdotal, but my impression among my relatively liberal social and secular social circles has been that having more kids does raise status for women, all else equal. Also, it is a more reliable path to increased status than trying to gain status through professional achievements; unless you are something like a CEO, or you have a high prestige and interesting profession, people seem not to care about what a woman is doing professionally. But if you have kids, everyone wants to ask you about the kids, and see them, play with them, talk to them, etc. Nobody cares if you are a highly compensated attorney, nobody wants to hear about it. I think this jibes well with the figure that 86% of women ages 40-44 have given birth. So maybe some future cultural evolution will be more women emphasizing motherhood as opposed to career, as we move on from the period of time when the professions and corporate careers were opened up to women and new and exciting, to where we have a relatively long and established history of women in the professions and corporate careers, and women take a more cold eyed look at what they can and cannot likely expect from their choices.
A lot of the status and satisfaction from having children can be achieved by having a single child. Two at absolute most. In fact having only one kid opens up certain social status options that aren’t available to larger families. You can afford private school tuition (which scales linearly). You can make do with a smaller living space. You’ll note both of these are really important in an urban environment where space and good school districts are scarce and expensive.
I’m not saying more kids doesn’t bring more joy, only that under certain circumstances its not such a surprise to see all these single child families amongst liberals, and almost no 3+ kid families. You’ll note that in a society where some people don’t marry and have children, everyone who does having merely having two kids will mean lower than 2.0 TFR.
Tyler always used to say that liberals are more afraid of a disappointing child than afraid of having fewer children. I think that makes sense. Getting three kids into Harvard doesn’t garner more status than one, but having one black sheep ruins the other two. At least in the liberal mindset.
The conservative pro-life attitude is about more than abortion, it really is a totally different mindset when it comes to having children.
Then of course there is age. When you start having kids late, you tend to have fewer kids. Part of this is women’s biology. Part is a lack of youthful energy to keep up with kids. There are all sorts of reasons. But when you get started late you tend to have a small family.
I agree with at least some of what you are saying. I guess that one thing that I would predict is that if we have a persistently tight labor market, we will see more people marrying and having kids at younger ages, and hence more kids overall, just like happened in the 1950s during the rebound from the Great Depression. Also, I would expect the slow shifting of population away from expensive metros to have both some impact through people having more space, but also having an impact in terms of norms (a lower share of people living in metros that obsess over educational credentials).
Some of the economic forces pushing people into urban metros (and a limited number of them) are independent of fertility trends discussed here. Also, the labor market is only “tight” for those that have the kind of skills that gravitate towards those same metros.
I suspect that immigration will short circuit the effects you’re hoping for. They will keep labor markets from getting tight. They will crowd into already crowded areas.
In a globalized sense…high TFR groups will replace low TFR groups. However, that might not mean that conservatives replace liberals. It could just as easily mean that the global south will replace the global north.
There is no myth of falling fertility. But uf course, there is an inverse relationship of high income and low fertility per nation. It is clear as cloudless day and it really is a contradiction the richer we are the less we can afford children. So why do capitalist societies with incredible production capabilities have the reality that people are having less children than they desire:
1) Capitalist societies through price can control the expensive items. And kids are increasingly more expensive so this is a way for a family to control cost. Kids are more increasingly expensive because now people want more education and healthcare not just food and housing.
2) Capitalist are smarter but more technocratic in their decision making that includes children and marriage. Note the age of first marriage is pushed out to thirty as divorce rates are declining.
3) The opportunity cost of mother job is a lot higher.
4) The cost of not getting an education is higher to most people.
5) Finally, most of the production and resources are going to the top 20% who can afford to have more expensive children while the bottom 80% are learning to have less.
Doesn’t this prove too much? If fertility/fecundity were heritable, then why has it been decreasing in the first place?
Because of environmental change. Traits that were adaptive in the ancient environment (e.g. eating the sweetest foods available, having self-control where sex is concerned) became maladaptive when candy and condoms were introduced to the environment.
Not sure this answers the question. If what you say is true, and high fecundity/fertility is now maladaptive, then why are the authors treating high fecundity/fertility as causing a population surge?
You’re getting it backwards. Creating viable copies of your genes is by definition adaptive. Traits like a sweet tooth or self-control may or may not be adaptive, depending on whether they lead to additional viable copies of your genes. If a grape is the sweetest thing around, a sweet tooth promotes good nutrition, good health, and is adaptive (i.e. likely to promote reproduction). If your environment has candy, then the same trait leads to obesity and diabetes (and few offspring).
Over time, whatever traits are adaptive will become more common in the human population* – they lead to copies of themselves.
*Averaged over the environments experienced by that population over the period in question.
Not really. The assumption is that this subset of folks that are having a lot of kids today are not (and their offspring will not be) subject to the same environmental pressures that everyone else who has had fewer kids is facing.
@taimyoboi: They will be in the same environment* and subject to the same pressures, but the ones who thrive in that environment will be the ones whose traits are adaptive in that environment. Adaptive traits may include having a distaste for very sweet foods, avoiding birth control**, or something else entirely. Whatever makes the most copies of itself in the environment at hand.
* Assuming the environment doesn’t change again, which it may.
** Possibly due to religiosity, possibly due to shortsightedness. Whatever gets the job done.
It makes more sense when you realize that nearly all behavioral traits have a substantial genetic influence.
http://journals.sagepub.com/doi/pdf/10.1177/1745691615617439
Women should be wage-slaves, not mothers!
At least, feminists equal to men should be — you don’t see men being mothers, do you? But lots of them are wage slaves …
I think one part of the #MeToo movement and the rage is that the reality of being at work in a nearly dead-end job, like male farmers >> male factory workers >> even male entrepreneurs in the 4 of 5 startups that don’t make it past 5 years, that reality is getting old for a lot of college educated women. Instead of having it all, great career and great family, many are in wage slave “not to be a VP, ever” tracks, plus way, way past their prime marriage and baby making age. An increasing number of them will be choosing more motherhood over rat race. Or their younger and more attractive siblings or cousins or non-related coeds will be wisely learning the lessons of corporate impotence that so many men have so often learned, and choosing less than upper or upper-middle class, to have more quality of family life.
The pro-life, pro-family families are also likely to have about a 1% or more greater fertility, and they’re more likely to raise pro-life kids. (Bayesian prior estimate — anybody have better figures for pro-life fertility vs pro-choice?)
We need culture change — and Trump / Brexit / Central Europe populists — this looks like the culture is changing, to me. With the prior culture elites not liking it.
Demographics is destiny (we have 4 kids).
For most of the ten thousand years since the development of agriculture population grew very slowly. Individual women might have multiple pregnancies, but war, famine, pestilence, and environmental disasters kept population growth quite small. Then technology, science, medicine allowed a real growth spurt. Perhaps the “natural” state is not population growth but steady state.
Malthus was right in the long term but just had really bad timing?
He wasn’t so much wrong as 200 years early.
I agree, with three caveats:
1) It is important not to confuse equilibrium with peace. From a total population perspective, it doesn’t matter whether (e.g.) Palestine is populated by Arabs or an equal number of Jews. From the perspective of a person living on that land, that’s all that matters, and we can expect them to use all the force and fraud they can muster to get the answer they want.
2) The increase in global population is substantially due to our use of fossil carbon for fuels and agricultural fertilizer. Unless adequate substitutes are developed, the current level of population may not be sustainable.
3) Even before technology, nature was not entirely stable. Farmers had better and worse harvests; supplies of food and other necessities fluctuated and populations fluctuated along with them.