The Loom

When It Pays To Be Dumb

Intelligence is no different than feathers or tentacles or petals. It’s a biological trait with both costs and benefits. It costs energy (the calories we use to build and run our brains) which we could otherwise use to keep our bodies warm, to build extra muscle, to ward off diseases. It’s also possible for the genes that enhance one trait, such as intelligence, to interfere with another one, or even cause diseases. Over the course of evolutionary time, a trait can vanish from a population if its cost is too high.

On the other hand, intelligence may offer some evolutionary benefits, by allowing us to find food, withstand the elements, locate the car keys our children have put in their dollhouses, etc. But it is by no means a given that intelligence is always a net plus. It all depends on the conditions in which we–and other animals–find ourselves in.

Scientists have come to appreciate how optional intelligence is through several sorts of experiments. Last year French scientists reported an experiment in which they bred fruit flies for their ability to learn. They would give the flies oranges and pineapples on which to lay their eggs, but they would dab one kind of fruit with a nasty tasting chemical. Some of the flies learned quickly to avoid the bad-tasting fruits, avoiding them even when the researchers didn’t put the chemicals on them. These smarter flies were allowed to reproduce, passing on their learning genes to the next generation. (The researchers switched the bad taste between the fruits in each generation to make sure that the flies weren’t simply evolving a distaste for oranges or pineapples.) This line of flies became significantly better at learning than their unevolved cousins in a few dozen generations. And in a reverse experiment, they succeeded in breeding stupid flies who did worse at learning than normal flies.

If it was so easy for the scientists to produce better learning in flies, why hadn’t the ancestors of these insects already evolved this sort of intelligence in the wild? The answer is that this intelligence comes at a cost. The researchers put the larvae of the smart flies alongside some normal fly larvae and let them compete for a supply of yeast. They then counted how many of the larvae survived to adulthood. Then they did the same experiment with the dumb flies. They found that the larvae of smart flies are more likely to die off than the dumb ones.

Now comes another experiment in intelligence, this one conducted mainly by nature rather than scientists. Many of the streams that feed the Panama canal are inhabited by the same species of guppy, Brachyraphis episcopi. And in many of these streams, the guppies live in two different habitats: above and below waterfalls. Below the waterfalls, they face a lot of competition from other fish that are trying to eat the fruit and other foods that fall from the trees overhead, and they also have to cope with several predatory fish. But above the waterfalls the guppies enjoy a predator free existence. Researchers at the University of Edinburgh realized that this arrangement created excellent conditions for the evolution of different kinds of behavior within a species. Upstream guppies would not face the same evolutionary pressures that the downstream fish were. And if the researchers were right, they should find the pattern repeated in stream after stream.

The researchers netted guppies from four different streams, both from upstream and downstream populations. They then shipped the fish back to their lab in Scotland and tested their ability to make their way through mazes to find food. As they report in a paper in press at Behavioral Ecology, the fish from the low-predator upstream sites consistently outperformed their downstream counterparts. They figured out the mazes twice as quickly.

The researchers argue that the upstream fish do so well because they have been able to evolve a sort of single-mindedness. In the wild, the guppies appear to size up their stream and figure out the best place to wait for food to drop to the water. They head for that patch quickly and defend it from other guppies. This sort of learning translates well into a laboratory maze. The downstream guppies, on the other hand, would risk becoming easy prey if all they did were to search for the best patch of stream. Instead, they also have to get a better sense of their overall habitat, spotting predators, finding refuges, and so on. In the laboratory, they tended to explore more of the passageways of the maze than the upstream guppies, perhaps due to their instinct to get a lay of the land (or perhaps the lay of the water).

These results raise a sticky point about ourselves. They suggest that different populations of the same species (such as humans) can evolve differences in cognition in response to different environments. I don’t think these results can be used to boost any notion of race-based difference in IQ, though, because we’re not fish or laboratory fruit flies. I don’t think the conditions that people in different parts of the world face are as different as these flies and guppies have faced. The most important lesson from these results, I think, is make us tone down our self-love a bit. Being intelligent does not make us superior to other animals. It only makes us superior in one respect.


  1. #1 vernaculo
    December 17, 2004

    Faced. Not now. Then. Upstream humans and downstream humans. It has nothing to do with value, except here, now. Which we’re sort of taught is all there is and will ever be, but it isn’t true. Big dumb aggressive athletically superior humans will prosper in the appropriate conditions, as will small cunning intelligent humans. But they won’t be the same conditions.
    The conditions in which we now live are the right niche for certain kinds of behaviors and abilities, and people hard-wired with those abilities prosper, as do people who can learn them. We’re super-adaptive generalists, you’d expect our genetic toolkit to be well-stocked and full of surprises.
    But it’s past time to stop pretending there’s only one kind of human being, and that all humans respond the same to any given circumstance, using the same innate abilities.
    What the eugenicists always miss is the complexity of the genome, the immense possibilities we carry. The upstream and downstream guppies came from the same forebears, for all their present differences.

  2. #2 John S Bolton
    December 17, 2004

    It may be that , presently, we do not have a model of what sort of reproductive isolating mechanisms would prevent a potentially very advantageous character, such as higher intelligence, from spreading into the equatorial regions where it is said to be relatively undeveloped. Considering the powerful influence of parasites of all sizes, to push any species in directions that one might otherwise call unlikely, what if resistance to tropical parasites, and northern-adapted immune systems, cannot both appear at their best in the same individual? It is known that northern-adapted peoples cannot live in malaria-infested districts without using precautions that tropical-adapted populations don’t strictly need. The genes allowing for above-average intelligence would be those which protect the infant’s fever-damageable brain, with DTH appearing strongly even before antibodies. The northern-adapted populations, especially those long-urbanized, have escaped tropical parasites, and needed DTH against pathogens like TB, measles ,smallpox and other crowd diseases. The connections of these specialized resistances could be tested in cell cultures and correlated with intelligence. Then again, our truth-seekers may not want to know what made these differences.

  3. #3 Xguy
    December 17, 2004

    According to the research below, the reason why primates evolved higher intelligence seems to be so that we could successfully deceive each other:

    Neocortex size predicts deception rate in primates

  4. #4 Highly Bemused
    December 17, 2004

    “higher intelligence, from spreading into the equatorial regions where it is said to be relatively undeveloped.”

    “Said to be” by racists such as yourself (yes, that’s what you are, I’ve read your GNXP comments often enough to be certain you qualify.) Why the weasel words about what are in fact your personal beliefs?

  5. #5 nguyenngocduc
    December 17, 2004


  6. #6 onetwothree
    December 17, 2004

    The flies were not bred with superior “smart”ness, but were merely given a new instinct. There is a difference between intelligence and instinct.

  7. #7 TangoMan
    December 17, 2004


    To branch off on the behavior tangent, I found it interesting that selecting for behavior in foxes results in physical changes including brain chemistry.

    “By intense selective breeding, we have compressed into a few decades an ancient process that originally unfolded over thousands of years,” writes Trut. “Before our eyes, ‘the Beast’ has turned into ‘Beauty,’ as the aggressive behaviour of our herd’s wild progenitors entirely disappeared.”

    But that wasn’t the only change. Breeding foxes to strengthen a single behavioural trait also brought about a wide variety of physical changes seen in many animals that become domesticated.

    Their coat colour, used among wild foxes as camouflage, changed. Irregular splotches of white fur appeared in the domesticated foxes. Their ears became floppy, replacing the straight ones of wild foxes. Their tails began to roll, similar to those in some dog breeds. Their tails also became shorter as did their legs. And although the geneticists didn’t select for size, the domesticated foxes were slightly longer on average. Their craniums also changed so that the males became somewhat feminized and both sexes became more dog-like.

    Reproductive cycles were also affected. The domesticated foxes reach sexual maturity a month earlier than non-domesticated foxes do and give birth to litters that are, on average, one pup larger. Even the brain chemistry among the docile foxes changed. Compared with a control group, their brains contained higher levels of serotonin, a neurotransmitter thought to inhibit animals’ aggressive behaviour.


    I think that many people hold “different environments” to a very high standard. As the fox example demonstrates, a different environment can be a situation that elicits a different behavior that rewards reproductive success. The unintended consequences of that selection pressure are hard to predict.

  8. #8 Steve Sailer
    December 17, 2004

    You can think of the narrow-minded high IQ fish above the waterfall as the Nerd Fish who live in a safe enough environment where they can concentrate single-mindedly on just one job, whether searching for food or programming a computer. In contrast, the fish below the waterfall are the Big Men Fish who live in an environment where “situational awareness” is as important as it is to a fighter pilot or a point guard, so therefore they aren’t as good as “single-tasking” intellectually, but are better at “multi-tasking,” which is harder to measure using standardized tests than is IQ, but is still a very important mental skill in hazardous environments.

    Here’s my Nerd vs. Big Man theory as it plays out in the political world:

    And here’s how the Nerd vs. Big Man theory works in sports and business:

  9. #9 David
    December 17, 2004

    Pay no attention to the man behind the curtain.

    Have you read what you just wrote?

    You don’t think that, oh, people living in an urban environment with civil servant exams for 2000 years (the Chinese) might be facing different challenges for reproductive success than people trying to avoid being stampeded by a rhino or eaten by a leopard?

    You might want to ponder more deeply the different environments humanity has experienced during our development as a species. We do, after all, occupy every continent except Antarctica and have done so for about 10,000 years. No opportunity for experiencing different pressures there? Malaria? cold adaptation? how about those diabetes rates in Southwestern American Indians?

    But heavens no, pressures that could produce sickle cell disease and diabetes could not POSSIBLY have ANY effect on IQ. No sirree.

    Oy. you’ve got to be kidding me.


  10. #10 Jason Malloy
    December 17, 2004


    This is a pretty terrible version of history, and why the attitude?

    I don’t believe there is a scientific answer to the question of how different human selection environments have been to result in differences in a trait such as intelligence. We just don’t know enough about human intelligence to know why it has the structure we think it does (i.e. quantitative trait with a surprisingly high heritability). For instance it seems plausible (to me anyway) that outside of modern industrial societies where intelligence is inversely related to fertility, higher general intelligence would have almost always been a fitness maximizer. But this raises the question of why all the variability wouldn’t be quickly selected away? Economist Ed Miller has tried to answer this with a Red Queen scenario. In short, I don’t know any reason why intelligence should be variable for humans in any specific world environment for the same reason I don’t know why intelligence should be variable *at all*. If cold environments were more conducive to intelligence than warm environments I imagine we should see this with animals in the wild, or (at least) in laboratory breeding experiments. I have seen evidence from neither. Jared Diamond, on the other hand, reverses the typical supposition of genetically pigeon-holing the “haves” and “have-nots” by hypothesizing that the pre-modern environment of the Papuans probably selected for increased analytic ability. This too seems doubtful/unsupported (ironically, although intended as an anti-racist alternative to usual theories in this department, similar theories about the dysgenic effects of “domestication” were previously used to buttress anti-Semitic ideas. See for instance some of the embarrassing earlier writings of Konrad Lorenz).

    I think the best we can do with this question in a multi-racial society is to always emphasize just social policies and condemn unjust ones; legally challenge discrimination; provide special opportunities for those with histories of unfair treatment; while *also* taking the idea of possible variability in to account, and to put sufficient resources into testing it with the methods we have available. To quote Ernst Mayr:

    “Even though all of us are in principle equal before the law and ought to enjoy an equality of opportunity, we may be very different in our preferences and aptitudes [NB – he’s referring to race – JM]. And if this is ignored, it may well lead to discord.

  11. #11 John S Bolton
    December 18, 2004

    Replying to the ‘highly bemused': I am pleased to be an inspiration to your bemusement. To be thus bemused, though, could cause one to use a presumably ad hominem approach, when rational argument is not necessarily unavailable against my suggested line of inquiry. Assuming that this bemusement has not prevented one from spending enough time on college campuses, one may have acquired uncertainty as to whether the term racism is not one of the most equivocated to be often used polemically thereabouts.

  12. #12 harold hicks
    December 18, 2004

    Technically, the fruit fly work in particular studies “learning” rather than “intelligence” per se. “Learning” – modification of behavior as a result of a repeated environmental stimulus – is relatively easy to study. To be even more precise, the flies were selected for relatively rapid adaption to “operant” conditioning – in which the stimulus comes before reward/punishment (in this case, they taste the fruit first, find out it’s bitter next) – a form of conditioning often associated with the work of B. F. Skinner. (The other intensively studied form of conditioning is “Pavlovian”, in which the reward or punishment comes first – rats learn to rush forward at the sound of a bell because it has been consistently rung just before food appears, for example). The physiologic changes underlying conditioning are of great interest to neuroscientists, and the genetics of “fast-conditioning” or “slow-conditioning” flies could provide valuable clues. Conditioning is clearly a form of “memory”, and we may intuitively feel that it is a type of, or related to, “intelligence” as well (hence the researchers joking designation of the slow-conditioning flies as “dull”). Nevertheless, it is an overgeneralization, and anthropomorphic in the extreme, to insinuate that the fast-conditioning flies are analogous to “more intelligent” humans. Furthermore, the experiments actually show the powerful influence of the environment on behavior – all flies, fast- or slow-conditioning, learned to avoid an otherwise desirable type of fruit – something we would never see in unconditioned flies. This type of learning is the opposite of “instinct”, by the way – it is entirely a product of the environment.

    David uses these experiments as the prelude to the introduction of a stereotyped, inaccurate, and greatly oversimplified description of the respective histories of Africa and China (I don’t mean to sound insulting; I think this critique is accurate). Both Africa and China are geographically vast, diverse, and ancient. Nor would his sweeping conclusions about human genetics be warranted even if his historical summary were accurate. It is difficult to avoid seeing this as an attempt to justify applying racist stereotypes to modern people of African or Chinese descent.

    Steve Sailer’s contribution is, unsurprisingly, amusing, yet laden with racist implications. In the end, though, it is nothing but a false analogy. The experiments he alludes to tell us a great deal about the guppies in question, and broadly support the principle that behavioral tendencies can have an inherited component (something almost no-one denies). They may even point the way to understanding some components of what we call “intelligence”, with the caveat that we have a great deal of trouble defining and limiting exactly what “intelligence” is. It is not logical to suggest that upstream guppies are biologically similar to human computer programmers. If it weren’t for the racial stereotyping implied by its creator, this might be considered an imaginative literary comparison, but it is by no means a rational scientific conclusion. Also, Mr Sailer seems to overlook the fact that in humans, the traits he alludes to are not mutually exclusive. It is perfectly possible to be a fighter pilot and also a good computer programmer.

  13. #13 Paul
    December 18, 2004

    There are some serious issues here in ascribing taste avoidance and curiosity with the moniker of intelligence.

    How is it not know that the fruit that “learned faster” did not merely evolve to have better taste perception or taste avoidance? Did they test the smarter fruit flies against other types of bad tastes?

    As for the fish, simply stating that fish with a greater curiosity are “more intelligent” might be reaching. It could simply be that the fish strain at the bottom of the waterfall are more impulsive, in which case a two-year old child is more intelligent than an adult.

    Or it might be that the fish above the waterfall are more sedate in the behavior, in which case a St. Bernard would be seen as less intelligent than a Chihuahua. I just feel there are other ways of interpreting these results than jumping on the intelligence conclusion.

  14. #14 razib
    December 18, 2004


    well, a normal distribution of a trait implies usually that its fitness implication is not that strong in one direction otherwise it would fixed into one phenotype and become “genetic.” the link you provide uses the model of balancing selection, but i think the conception of “one environment” is problematic, not only is there are a great deal of social detail in many world societies in a narrow geographical expanse, these social variables alter in weighting as a function of time. the normal distribution of intelligence might be ‘metastable,’ that is, an artifact of various social conditions that are always in flux which increase and decrease fitness of various genetic conformations.

  15. #15 Jason Malloy
    December 18, 2004

    J.L. Gould and C.G. Gould’s The Animal Mind is an excellent primer on the controversies and suppositions of animal cognition, including the often amusing debates about instinct vs. intelligence in various species (Kohler’s chimps, etc).

    Of course since mice have an intelligence structured much like humans’, perhaps a test of geographic heterogeneity with this animal could tell us more about what identifiable selection pressures, if any, could be relevant to this sort of cognition.

  16. #16 Paul
    December 19, 2004


    Thanks for that response. I figured there was some kind of book like that out there. There’s one other snit I have with the first study.

    It’s a bit reaching, again, to imply that the higher larval suvival rate of the “dumber” flies means that “smarter” flies have decreased their fitness. Larval survival rate is only one fitness endpoint. Across the complete life cycle and taking into account multiple end points (pupation rate, number of eggs laid, etc…) the “smarter” flies might have a higher fitness.

    This issue pops up alot in the medical literature, where you can get different conclusions depending on which question you ask and which endpoint you choose to define success in a drug trial. A drug that causes a higher remission rate of tumors might also have a lower six month survival rate in patients compared to other drugs out on the market.

    It depends on which end point you choose. And larvae survival is only one endpoint.

  17. #17 NuSapiens
    December 19, 2004

    Another explanation could be that the upstream guppies were more curious (or, less timid) in the absence of predators. If this is extended to human evolution, it should be noted that a consistent behavior of modern Homo sapiens (at least in the Northern hemisphere) has been killing off potential predators. Being a “nerd” constantly meditating on thoughts is a hazard even in dangerous urban areas, so safety could be a prerequisite for intelligence to survive or express itself in populations.

    The other point to emerge from this is that intelligence might not be favored by Darwinian evolution, and very smart people might exist just by accident and by virtue of large modern population sizes. In this case, human societies “laissez-faire” vis-a-vis their most intelligent members at the cost of losing that intelligent minority.

  18. #18 kanaanp
    December 19, 2004

    Does natural selection still drive human evoluion? Reproductive success? Haven’t we passed the threshhold of adaptability where ruthless infant mortality would shape our populations? I can’t imagine astigmatism surviving more than 1 or 2 generations in any animal species dependent on vision for survival. But any human can go to an optometrist, and the big dumb aggressive guy can higher an accountant.

    My take, going back to Ardrey, is that adaptive intelligence is relatively habitat-neutral compared to adaptive instincts, which require a stable environment over time to evolve. Polar bears wouldn’t evolve if their surrounding colors changed from white to brown every few generations. That’s why humans have such sloppy habits of predation and sex–we evolved during a period of environmental flux where no single mating or hunting pattern could emerge as a clear advantage. In a more stable habitat over time, the urge to kill and fuck indiscriminately wouldn’t yield a dominant species.

    That’s us in a nutshell – social bi-peds with fine motor skills, sexually confused, indiscriminate killers. All the rest is just evolutionary window-dressing.

    I don’t think a genetic theory of history makes much sense.

  19. #19 John S Bolton
    December 19, 2004

    An anti-genetic or anti-hereditarian theory of natural history is guaranteed to be nonsensical. Recorded human history has events at the periphery, which are nevertheless momentous, and which only genetics can explain. The amerind and other aboriginal morbidity events, are some big examples. Others include the failure of Europeans to colonize the tropical lowlands, on spite of many attempts over centuries, and only genes can explain that. The sum of such examples of dramatic population-genetic mismatches to environments of pathogenic intensity, may add up to the reproductive isolating mechanisms which maintain differences. Can tropical-adapted populations acquire the strongest TB-resistance genetically and maintain the best natural malaria resistance, and in the same individuals? If this can happen, science should be able to find an individual with both specializations.

  20. #20 Jason Malloy
    December 19, 2004

    I just remembered one highly interesting,
    putatively selection-based, cognitive difference between human ancestral groups (I’m sorry Carl, this is Pandora’s Box – I’m just too interested in this topic!). Australian Aborigines have an extraordinary aptitude for desert/barren landscape navigation, and this also translates into scores on visual memory tests that are about 50% higher than Caucasians’ (this is mentioned, for instance in the wonderful new Smithsonian book Human).
    Sydney neuropathology professor Clive Harper extended this knowledge a bit by finding[1] that the Aboriginal visual cortex is also, on average, about 25% larger and contains more nerve cells. This topic is still pretty hot (for obvious reasons), so I read that this research had trouble getting off the ground/continuing.

    [1]Harper, C. G. and L. A. Mina (1981). A comparison of Australian caucasian and aboriginal brain weights. Annual Meeting of Australian Association of Neurologists, Adelaide, Clinical and Experimental Neurology.

    Klekamp, J., A. Riedel, et al. (1987). “A quantitative study of Australian Aboriginal and Caucasian brains.” Journal of Anatomy 150:

  21. #21 vernaculo
    December 20, 2004

    Harold Hicks-
    I won’t pretend to be qualified to agree or disagree with your main critique, though it seems accurate to me overall; but that last statement reads just as “morally” valenced as the work of the people you criticize.
    Yes, people can be fighter pilots and computer programmers both, as far as learned skills and innate potentials go.
    But people can also be Korean and Irish both, or aboriginal Australian and Italian, or a triple-digit mix of all globally-available categories(see New Orleans and Marseilles).
    That doesn’t answer the socially-disquieting question at the heart of Zimmer’s post.
    Substantial genetic differences in human beings do exist.
    We know this sub- and supra-rationally, but we’re prohibited from discussing it rationally, in public. The excuse is that it empowers the racist and eugenicist, because it does. Though a little common sense should clarify that – the selfish view of the human enterprise that underlies both is masked by a kind of altruism that’s centered on a larger than personal chunk of the genome. But it’s still selfish in its origin, and it’s still misguided because of that selfishness.
    That prohibition masks the actual racist and eugenicist attitudes and actions that have, and are, taking place, and it prevents any kind of hierarchy from being held up publicly, though more than a few are, privately.
    Preventing people from making hierarchies of human qualities doesn’t make things better for all of us, though it does improve the lot of some. The danger of simplistic scales of value that ignore the intricate mysteries what we are and can become don’t outweigh the dangers of delusional homogeneity.
    Pretending those qualities can’t be linked to reproduction – or that there are only superficial racial differences – doesn’t make it easier for us all to get along, but it does make it easier for more subtle racist processes to exist, hidden and undiscussed.

  22. #22 William Gruzenski
    December 22, 2004

    And yet, it is said that to ask a question from the compost of accepted ignorance is the first step out of illusion. Be it a different level of reality than the issue of intelligence, in terms of evolution taken blindly: who is the more advanced? Let us remember then how much we have learned; let us remember how little we know.

  23. #23 Sarah Dempsey
    December 25, 2004

    The learning and knowledge that we have, is, at the most, but little compared with that of which we are ignorant. We need to apply ourselves both now and in the next life. Without effort, we cannot be prosperous. Though the land be good, we cannot have an abundant crop without cultivation.

  24. #24 vernaculo
    December 27, 2004

    Let us forbear the use of contractions, for verily, there is no precedent for the contraction, as there is no precedent for the automobile or the atomic bomb. On our own on those, are not we?

  25. #25 AH
    December 30, 2004

    “delusional homogeneity”

    Says it all about 75% of the discussion.
