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.

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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?

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

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

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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...

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Who Wants More Kids?

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

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Find some issue on which women's opinions are the more correct onesThat 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.

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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...

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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.

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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.

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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.

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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.

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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/wik...

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.

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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.)

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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?

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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.

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