Biased Birth Rates

In poor societies richer couples have more kids, but richer societies have fewer kids.  This may be because female kid desires are biased low, relative to genetic interests, and in rich societies women have more relative power.  Ted Bergstrom explains in the May American Economic Review:

The demographic transition … presents a challenge to … evolutionary theories of reproductive behavior.  In Western Europe, starting in about 1870, real wages began to rise about 2 percent per year.  Net reproductive rates fell from an average of three children per woman in 1860 to fewer than two in the modern era. … Evolutionary biologists find it puzzling that a species reproduces less rapidly when individuals have access to more material resources. … Why was there a positive correlation between wealth and fertility before the demographic transition, but not after? …

Because of a genetic conflict of interest between mates, evolution could have shaped preferences so that "human females would fail to bear the optimal number of children in the absence of pressure of mates and kin."  …  Thus men would desire more children and women fewer children than their own genetic interest dictates.  Differences in birth rates across time and between cultures would occur as one side or the other gains increased leverage in this tug-of-war.  In modern economics, women have increased influence in household decisions and, together with improved contraceptive technology, have gained greater control of their own fertility.  …

Malaysian husbands want more children than their wives and, when measurable household bargaining power favors the wife, a couple tends to have fewer children.  In a survey of Brazilian households, … as the ratio of the wife’s nonlabor income increases, couples tend to have fewer children. 

I’ve long been puzzled by the demographic transition, and so am excited to hear of a plausible theory that roughly fits people I know.  If it is true, and if we now have too many or just enough kids, relative to a social or moral optimum, then empowering women has helped.  But if, as I suspect, we now have too few kids, then empowering women may be largely to blame.

Added: Bergstrom credits Barkow & Burley. Ethology and Sociobiology, 1980.  If you want to play "find a better theory," at least try to explain all the related data, including fertility of the rich in poor societies, and the robustness of the demographic transition to cultures and contraception technology. 

GD Star Rating
loading...
Tagged as:
Trackback URL:
  • Stuart Armstrong

    Can we find a trade? Find some issue on which women’s opinions are the more correct ones but male influence is high (foreign policy springs to my mind) and offer female influence there versus male influence in quantity of children.

    Of course, the actual trade will have to be made by a series of incentives and rules on both issues, so it might be argued that we could make the right things happen in either case anyway – but this gives us two right things for the price of one, and everyone feels they’re vindicated.

  • Hopefully Anonymous

    Stuart, very impressive resume/cv!

    As for this topic, I think we’re throwing away a lot of existential problem-solving power by not (at the least) creating strong incentives and structures to maximize off-spring of the most talented existential problem-solvers alive today. Mr. Y1, Y2, and Y3 Ph.D. and Ms. X1, X2, X3, X4, X5, X6, X7, X8, and X9 Ph.D., twelve of the leading economic growth theorists alive today for their respective genders, could between them produce a next generation of more than 900 offspring (through in vitro fertilization and surrogate motherhood), which will probably be more talented at innovating ways for us to improve on economic growth as a class than 900 offspring randomly from the population.

    Perhaps we’ll have the talent of all of current humanity in something the size of pen for the cost of a penny in 20 years, if Kurzweil’s theories are correct. But if not, we have a relatively cheap way to replicate, to a degree, the most useful computing devices known in apparent reality: the brains of people very talented at solving the existential and other challenges that we face.

  • http://www.nancybuttons.com Nancy Lebovitz

    What do you mean by a social or moral optimum number of children?

    My guess is that the original biological incentives for having children were a combination of liking sex and a very moderate fondness for children. Birth control has affected the way those balance out.

    Modern society has weakened many of the incentives and raised the costs for having children. Pensions (both private and government) mean that you aren’t absolutely dependent on your kids for help in your old age.

    Your kids will almost certainly move away. This means that if you like them, you won’t be seeing as much of them as you (and quite possibly they) want. If you wanted to have a right to use them as spiritual scratching posts, they can get away from you.

    The pressure on parents to have kids that turn out well has gone up. The costs of educating kids has gone way up.

    My notion is that we’re going through a bottleneck which is selecting for people who *really* want to have kids.

  • michael vassar

    If we are trying to maximize the utility of existing humans I don’t know what the optimal birth-rate is, but my guess is that efforts to produce it would be politically far too costly to be taken seriously as a means to the relevant end.
    If we want to maximize aggregate human utility, we almost surely have far too few humans being born in rich countries.
    If we want to maximize aggregate utility period, we need some way of sensibly trading off utility between organisms.

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Nancy, yes, birth control, pensions, and mobility have had effects, but the demographic transition has reliably happened even when such effects have been weak.

    Hopefully, yes, there is a separate issue of which kids a society should have.

  • http://www.timworstall.com Tim Worstall

    I’ve always approached this from the point of view of opportunity costs.
    First, a note: if you Google “desired fertility” you’ll come across a paper which insists that 90% of changes in actual fertility are as a result of changes in desired fertility. Contraception helps, but a lot less than many think.

    To opportunity cost. The aim of life (in an absurdly reductionist Darwinian sense) is to have descendents. It’s not that long ago that in order to be reasonably certain of doing so one needed to have 5-8 births per married woman for said woman to have second and third generation descendents (from Greg Clark’s upcoming “A Farewell to Alms). This started to change about a century ago (US and UK etc, maybe 150,) and much more recently in some other places.
    There is a correlation (no, of course I have not shown causality, I’m an amateur!) between the rise of public health (and thus steep drops in child mortality) and the “next” generation having fewer children per marriage.

    So, the cost of reaching the goal (grandchildren) has fallen as more of the first generation survive…one needs to have fewer children to reach the goal.

    It’s also true that another effect of the empowerment of women is that they get to do more interesting things these days than simply pump out babies.

    So, purely an amateur view, but I would say that the opportunity cost of having many children has gone up (all those other things not done) and the opportunity cost of having few (the liklihood of not having grandchildren) has gone down.

    In such a situation, wouldn’t we expect families to be smaller?

  • http://profile.typekey.com/sentience/ Eliezer Yudkowsky

    Worstall, the optimization criterion of natural selection (you can’t call it a goal) is to have as many descendants as possible. It’s not like a human who says, “Gee, I’ve achieved my goal, what next?” Evolution is not a satisficer. The criterion is unbound and unlimited and if an allele has 1% more descendants than its alternatives, it can become universal in the gene pool over time. This is what makes dropping birth rates a puzzle.

    (Actually, the optimization criterion of natural selection applies to alleles, not individuals; if you took the individual viewpoint at all you would count the number of relatives surviving into a given generation weighted by their relatedness, not just direct descendants, but mostly you would just count gene copies.)

  • Pseudonymous

    It does not follow that individuals have an inherited desire to have as many children as possible anyway. For most species a desire to have it off with the opposite sex whenever you come into heat is probably good enough.

    Consider the difficulty we have getting some species to reproduce in a zoo.

    (I think Desmond Morris described a city as a human zoo.)

    As for the effects of feminism…

    IIRC the fertility rate in Iran was ~ 6 just after the Iranian Revolution and is now 1.71, according to wikipedia: http://en.wikipedia.org/wiki/List_of_countries_and_territories_by_fertility_rate

    I find it hard to believe that that change was due to changes in womens empowerment.

    The figures for rich countries (post-transition) do not obviously show that more “feminist” countries have a lower fertility rate than less “feminist” countries (eg Japan, South Korea and Italy have a lower fertility rate than the US or UK).

    Is there any evidence that women desire children less than do men, closer to home than Malaysia and Brazil? People have been known to look for results to prove their theory…

    The traditional explanation of the demographic transition (at least, the one I vaguely remember being told in school) was that peasant households can use children on the farm, so they do not cost that much (the value of their labour is comparable to the cost of their food).

    In the cities of the early Industrial Revolution, children were still sent out to work, so large families would still be relatively cheap, even for the poor.

    Now that people do not enter the workforce until they are 16-25, they are a larger item of household expenditure. So if people do not want children for themselves any more than they did before, naturally family sizes will tend to drop.

  • http://bbnflstats.blogspot.com Brian

    Why is it assumed that wealth is the driving factor? What about medical advancements? Modern parents are far more assured that their children will reach reproductive age themselves.

    If we want “as many descendents as possible,” that might not mean as many children as possible. It may mean ensuring that a small number of children reach reproductive age with suitable enough resources to attract a mate and support their own children.

  • David Johnson

    Evolutionary biologists find it puzzling that a species reproduces less rapidly when individuals have access to more material resources.

    There are lots of plants that reproduce more in harsh conditions. Want lots of roses? Be harsh to your rose bushes! A lot of grasses are this way as well. Don’t water your lawn and it tends to go to seed. Pamper your lawn, and it will be nice and lush but it won’t head out.

    In the case of humans, however, it’s not that more prosperity causes less sex. It’s just that we are consciously choosing to have fewer kids.

  • Hopefully Anonymous

    Elizier,
    I don’t think it’s much a puzzle. I think the emergent phenomenon of genes has just run up against the emergent phenomenon of subjective consciousness. Subjectively conscious beings engage in their own decision making criteria, unlike apparently non-reflective allele propagators like ameobas. Otherwise more ordinary men would max out on fertility clinic sperm donations and more exceptional people would engage in tactics like Dr. Cecil Jacobson. Even now, some transhumanists are talking openly about substrate jumping by “uploading” themselves -those aren’t subjective conscious entities that care too much about allele propagation.

  • Norman Siebrasse

    There are two questions here, an evolutionary question – why are people not increasing the number of descendants when they have increased means to do so; and an economic question – if the desire for children is a normal good, why are people not having more children as they get wealthier.

    It strikes me that Nancy is right with respect to the evolutionary puzzle. Bergstrom notes that “Evolutionary theory predicts selection for genes that produce behaviour that tends, on average, to maximize the number of their surviving descendants.” He doesn’t say, nor should we expect, selection for a desire for children per se. It seems pretty clear that the major behavioural adaptation for producing descendants is the sex drive. Bergstrom continues: “This theory suggests evolution would select for individuals who act as if personal consumption is not an end in itself, but rather an instrument for reproductive success.” Read “getting sex” for “reproductive success” and the evolutionary puzzle disappears. There has been no “sex drive transition.”

    Substitution effects seem like a very likely answer to the economic puzzle. Nancy’s suggestion of pension substitution strikes me as at least as plausible as Bergstrom’s argument of a substitution from men’s to women’s preferences, but it could be some of both. In any event, neither of these explanations of the demographic transition requires an evolutionary shift in the underlying preference for children.

    There is a relationship between the two. If all substitution effects can be ruled out then we would be forced back on a preference shift explanation, which would itself require an evolutionary explanation. But we’re certainly not at that point yet.

    There is an important evolutionary issue here, though. With effective birth control decoupling sex from reproduction, and economic factors apparently leading towards lower birth rates, the sex drive is becoming less effective as an adaptation for reproduction. I would expect selection for other types of adaptations leading to more children; perhaps a preference for more children per se, or maybe something correlated with wanting children or ability to avoid having them, such as selection for reduced impulse control, or reduced intelligence, or increased altruism.

    I think Nancy is right in suggesting that the demographic transition is a bottleneck. Demographers who assume that the demographic transition is a permanent facet of economic growth are entirely too sanguine.

  • Doug S.

    If children and their parents tend to have similar beliefs, then, in the long run, is democracy simply rule by the fertile?

    On an unrelated note, I wonder if, in the future, inability to tolerate hormonal contraception and allergies to latex will become more common…

  • TGGP

    Find some issue on which women’s opinions are the more correct ones
    That reminds me of Bryan Caplan’s research on political rationality which found that women think less like economists than men. One aspect in which this was interesting was that it had been assumed that women were less protectionist, because men see their wages hurt by competition, while women see the high prices in goods while they are shopping before their husbands get home from their protected jobs, but it turns out women are more protectionist. I suspect Stuart is right in that males are biased toward hawkishness.

  • http://econlog.econlib.org/archives/2007/07/who_wants_more.html EconLog

    Who Wants More Kids?

    It may well be the biggest puzzle in evolutionary psychology: Why do humans have fewer kids when they get richer,…

  • http://econlog.econlib.org/archives/2007/07/who_wants_more_1.html EconLog

    Who Wants More Kids?, Part II

    The GSS asks: “What do you think is the ideal number of children for a family to have?” So who…

  • Floccina

    Will the Mennonites (about 5 children per family) inherit the USA?

  • Floccina

    BTW Did not the fertility rate fall during the great depression?

  • http://www.sistahcraft.typepad.com sahara

    Doug, that’s interesting. One of the (secret) fears of the wealthy minority, is of the fertility of the poor, especially people of color. I chuckle in discussions, where after a couple of drinks, folks are honest enough to speak of being “overrun.”

    I live in a neighborhood where the fertility rate among immigrant groups of color is very high. Birth control and all that aside, you need to take into account cultural dynamics, and/or religion, which can stifle behavioral evolution. For many people of color, lots of kids is still seen as evidence of a man’s virility (hawkishness, Stuart?). And no, poor women secretly don’t want to have all these kids, that wear you and your reproductive system out. But what else do you have to show for your life, and how do you keep your man? Children are seen as a necessary blessing. This may seem simplistic to you all, but it is a reality for a vast majority of us.

    It should not be puzzling that having more material resources, means less kids. We’re not just economics, or genetics. For wealthier couples, less kids mean more discretionary income for themselves, and for the few kids they do have; consumerism, enjoyment, and quality of life, are the key words here. I have to explain this concept to my neighbors, who view this as selfish. As I have no kids of my own (partially due to economic factors), I am viewed as the epitome of selfishness. My behavioral evolution is viewed through lenses, varying from sympathy to hostility. I also have to explain to them that our history, economic and political policies have never favored large families, from the Irish Catholics to the present Mexicans, residing around me.

    There is a huge cultural and ideological gap in many of the theories I read and discuss; it’s a shame too, as the people who many academics render invisible, are some of the fastest reproducing folks on the planet. Maybe the meek will truly inherit the earth?

  • TGGP

    Maybe the meek will truly inherit the earth?
    Are you saying that the groups that reproduce the fastest have the lowest rates of assault? I think that might be the case for Mormons, Hassidics and Mennonites, but not lots of other groups.