Bryan Caplan  

Fruit Flies and Foresight; or, Evolution for Dummies

Free Responsibility, Con't... Old News...

A common objection to hereditarian theories of intelligence is that "Intelligence is SO important, evolution would have eliminated genetic variation." A simple fruit fly experiment (discussed in shows how wrong this is:

The team first bred a group of fast-learning flies. They allowed fruit flies to lay eggs on gels flavoured with either orange or pineapple juice. But one or the other was also spiked with bitter quinine. The next time round the flies were given the juice only - but some remembered which had previously been laced with quinine and laid their eggs on the other flavour...

After 20 generations, most flies from the selected line could learn the task in one go. They were not just better at tasting different juices or more averse to quinine, as ordinary flies could eventually learn to avoid the sabotaged flavour too, but it took them three to five sessions...

However, when the larvae of the more astute flies were made to compete with ordinary larvae for scarce food, fewer of them survived.

"They are slower at feeding," says Mery. He speculates that the flies may have to invest more energy in making or re-arranging connections between neurons in their brains, leaving them with less energy to forage when calories are limited.

Now I've never noticed that smart human beings are slower at feeding. But there is an obvious evolutionary drawback to human intelligence, too. Namely: Smart people are, almost by definition, more foresighted, which in turns leads to more responsible sexual behavior, and thus fewer children. In the National Longitudinal Study of Youth, for example, a linear estimate says that the most intelligent respondents have .88 more children than the least intelligent. Foresight has a lot of evolutionary advantages, but it's not a free lunch.

Of course, if you're really, really smart, you will be convinced by my argument that it is selfishly optimal to have more kids!

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Jody writes:

linear estimate says that the most intelligent respondents have .88 more children than the least intelligent.

I think you mean that the most intelligent have .88 times as many children as the least intelligent.

0.88 more children would contradict your point about there being an evolutionary drawback to intelligence...

Steve Sailer writes:

There's a correlation between IQ and brain volume in the, roughly, 0.3 or a little higher range when measured with the most sophisticated modern tools. Brain volume is expensive in terms of calorie consumption, so smarter people would die faster during famines if they couldn't use their brain volume to find more food.

Also, bigger skulls mean either more trouble birthing babies or longer periods of immaturity. People with big-headed babies need wider pelvises, which makes them slower runners.

Paul N writes:

Smarter human beings are reproductively deficient in other ways, too: they tend to stay home playing Dungeons and Dragons instead of mating :)

Jody: I think Bryan meant "0.88 fewer" rather than "0.88 more".

Brad Hutchings writes:

What a bad idea for an experiment!! Now with all these smart fruit flies out there, the next time the State of California decides it needs to kill them with malathion, they'll have to use Stealth fighters instead of regular helicopters to drop the stuff.

jaimito writes:

I am for more children, but the note is not convincing.

Foresight should cause the increase in surviving children. I think still it does.

Comparing the most moronic with the most intelligent is vorthless. Under IQ 60 people is unable to reproduce, specially males.

High IQ causes, in our society, less than average children. Particularly in females.

I am sure the author know all these but did not take the time to write an intelligent note.

David Friedman writes:

The argument is broader than "more resposible sexual behavior." The more intelligent person will be better at recognizing conflicts between his interests and the interests of his genes and evading the design features that exist to make him pursue the latter. There is a tradeoff between that and the advantages of intelligence--from the genes' point of view.

On the issue of head size and deaths in childbirth, my piece Why We are Getting Smarter suggests that the Flynn effect (rising IQ over time) could be due to improved obstetrics.

[Corrected URL: Why We are Getting Smarter. David: You have to include the entire URL, starting with "", for your clickable links to function. Your recent links have been starting with your internal folder structure.--Lauren Landsburg, Editor]

Alberich writes:

David Friedman,

Just to let you know I have clicked on a couple of your links but have only been led to "this page can not be found." It could just be me but in case other people are having the same problem I thought I would let you know.

Lord writes:

The intelligent just chose a different R strategy - fewer children but greater investment in them, consistant with their leadership position in society. There is more power in rule and wealth than in numbers.

Chris Bolts writes:

After reading your previous blog, Bryan, maybe the reason I am so focused on wanting five kids (1 now, 1 in the oven, three more to go) is that I am trying to maximize my utility of living a high quality life in my golden years. And just to illustrate this point, I compare and contrast my family and my in-laws. I nine siblings (five boys, four girls) and my wife has a brother and sister. Given this, one could probably expect my parents to have more grandkids and have a happier life, but they would be woefully incorrect: although my two oldest brothers have kids, they have problems with their babies' mothers which prevent the mothers from bringing the grandchildren around my parents, my parents shower my son with love that none of their other grandkids have been able to experience and because of this inefficient use of love and affection there is bound to be problems in the future with my son and my nieces and nephews.

However, my in-laws have five grandchildren, which will soon increase to seven and they thoroughly spread their grandparenting across each child, thus maximizing their love and affection across all of the kids and possibly avoiding any conflicts in the future amongst their grandkids.

However, there is another selfish reason for having more kids, but it is very controversial and so not to offend anyone I won't talk about it.

Half Sigma writes:

In our cave man days, intelligence must have contributed to a better chance of survival or more sexual partners.

In the 21st century, the less intelligent have more children, at least that's the case in the U.S. Survival of the fittest doesn't mean survival of those with the most admirable traits. Today, welfare moms are more "fit" to the environment than people getting PhDs.

eric writes:

There's a whole "optimal IQ" literature out there, where super braniacs seem to have this John Nash feast/famine aspect to them. I suppose you need a 160 IQ to win a Fields Medal, but I would guess the mean quality of life for these people to be below that of mean 130 IQ people. The ability to empathize, and thus manage, consort, and delegate, is probably decreasing at some level of IQ.

Jim Glass writes:

Ernst Mayr, who knew a little bit about natural selection, argued that it selects against intelligence. (Once notably in a on-line debate with Carl Sagan, giving a rationale for the Fermi Paradox rejoinder to the Drake equation that so impressed Sagan.)

Behaviors like herding, and organic structures as complex as the eye, evolve independently over and over and again -- but even normal mammal-level intelligence is rare among all species, and human-level intelligence seems a statistical aberration, one time among how many species over how long?

A big brain is very expensive in many ways, high calorie consumption, prolonged gestation, vulnerability of the mother, slow reproduction rate (small litters on top of long gestation), long vulnerable childhood, etc. For all those costs to be overcome by some benefit a large number of happy contingincies must fall into place ... so he said.

More recently, research cited in the Economist argues that females of easy morals select to reduce the intelligence of males generally. So if men are dumb we know whose fault it is.

(Although I think this line reasoning was on display back in the Revenge of the Nerds movies.)

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