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Too Hard for Science? The Genetic Foundations of Intelligence

The views expressed are those of the author and are not necessarily those of Scientific American.


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The scientist: Klaus Zuberbuhler, professor of psychology at the University of St. Andrews in Scotland, scientific director of the Budongo Conservation Field Station in Uganda, co-director of the Taï Monkey Project in the Ivory Coast, and deputy director of the Living Links to Human Evolution Research Center at the Edinburgh Zoo.

The idea: Scientists investigating the evolution of human intelligence often look at our closest ape relatives for insights. "By comparing chimpanzees and bonobos with modern humans, we can draw inferences about behavioral, motivational and cognitive traits that are ancestral, or shared with apes, and traits that are derived, or uniquely human, evolved during the last 5 to 6 millions years," Zuberbuhler says.

Ideally, researchers would like to see what effect genetic variations have on the behavior, motivations and cognition of healthy, normally developed individuals both within a species and across closely related species. Gene defects that lead to abnormal conditions "usually provide little help in understanding of how genes influence variation in normal individuals," Zuberbuhler says.

The problem: Ideally, to experimentally study each of the many genetic factors linked with intelligence, one would need individuals representing each of the untold numbers of combinations of these genes to observe the outcomes — and, really, multiples of each combination for experiments. Scientists would probably also not only like to see what happens with these combinations in one species, but compare results across closely related species, such as humans, bonobos and chimpanzees. Aside from the sheer logistical difficulties involved with finding or breeding such combinations, there come the moral and ethical questions of experimenting on model organisms with the level of intelligence one would like to study.

The solution? Scientists are currently surveying thousands of genes across humans and closely related species to see which might have changed over time and thus be linked with the evolution of human intelligence. They are also focusing on variations in genes that are strongly linked with cognition, such as FOXP2, Zuberbuhler says, which is associated with speech and language.

Image of Klaus Zuberbuhler from his Web page.

*

If you have a scientist you would like to recommend I question, or you are a scientist with an idea you think might be too hard for science, e-mail me at toohardforscience@gmail.com

Follow Too Hard for Science? on Twitter by keeping track of the #2hard4sci hashtag.

About the Author: Charles Q. Choi is a frequent contributor to Scientific American. His work has also appeared in The New York Times, Science, Nature, Wired, and LiveScience, among others. In his spare time he has traveled to all seven continents. Follow him on Twitter @cqchoi.

The views expressed are those of the author and are not necessarily those of Scientific American.






Comments 25 Comments

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  1. 1. eco-steve 11:43 am 05/30/2011

    Before we can search our genes for traits of intelligence, we must first agree on what we mean by intelligence. And first of all, can new intelligence be passed on through our genes?

    Link to this
  2. 2. eco-steve 11:44 am 05/30/2011

    Before we can search our genes for traits of intelligence, we must first agree on what we mean by intelligence. And first of all, can new intelligence be passed on through our genes?

    Link to this
  3. 3. toomepuu 12:27 pm 05/30/2011

    There is absolutely nothing hard about determining the traits for intelligence. The problem is, as is well known, that intelligence is not distributed equally among various racial groups. Thus it has become politically incorrect to even discuss it. Those that conduct good scientific work are frequently labelled racists, particularly by pseudoscientists.

    Link to this
  4. 4. Pugsley 1:24 pm 05/30/2011

    Research into intelligence, genetics, and race is the third rail of science. Those researchers risk never getting funded again, ostracizing and outrage by the less thoughtful members of the scientific community, and may even fired from their university – tenure or no tenure. The implications are just too horrifying.

    Good way to ruin a career.

    Link to this
  5. 5. daedalus2u 8:41 pm 05/30/2011

    The real problem is that the genetics of intelligence research is shoddy. Much of it is not even wrong. Some of these shortcomings are outlined in the recent Guest Blog post “The Politics of the Null Hypothesis”.

    The primary problem is with the whole concept of “g” and IQ. The idea of “g” is a myth. It is a statistical artifact of factor analysis. There is no such thing as “g” that can be measured.

    http://cscs.umich.edu/~crshalizi/weblog/523.html

    Look especially at note 2. The system is underspecified. If you have k tests, you have k individual factors for each of the tests, but k+1 unknowns, the k’s and “g” (if they were all linearly related but we know they are not). The system is under specified. There are infinitely many possible solutions that fit the data. With those degrees of freedom the “tests” can be made to do anything.

    This being the 21st century, with many genomes being fully sequenced, when I see a paper with the term “genetics of xyz” in it, I expect to see actual reference to actual genes. Are there any references to actual genes that show sufficient variation to explain intelligence differences? No, there are not.

    If differences in intelligence are due to genetics, then what causes the Flynn Effect?

    It is not being “politically correct” to call these researchers on their shoddy work, it is being scientifically correct.

    Professor Peter H. Shonemann (deceased) has been pointing out the weaknesses in these approaches to intelligence for decades. I recommend reading much of his work which is available on his website.

    http://www.schonemann.de//pdf/86.pdf

    The issues he raised have not been addressed. They are simply ignored and those who point out that they have not been addressed are then vilified as trying to stifle debate by being “politically correct”. No, we are trying to be scientifically correct.

    Link to this
  6. 6. Pugsley 10:27 pm 05/30/2011

    "If differences in intelligence are due to genetics, then what causes the Flynn Effect?"

    No researcher has said that genetics are the only factor. Straw man argument.

    Presumably the reason why there’s not a lot of specificity in determining the genes, is because it’s forbidden research.

    Is there a well-defined "g"? Perhaps not, just as there is no well-defined "mind".

    Link to this
  7. 7. daedalus2u 10:57 pm 05/30/2011

    Plenty of researchers have claimed that differences in IQ between populations (whites and blacks) are due to differential genetics.

    The Flynn Effect leads to larger differences in supposedly genetically homogeneous populations (i.e. whites and blacks) depending on birth cohort than is observed between populations (whites and blacks) of the same birth cohort.

    If non-genetic effects are responsible for a larger difference between different birth cohorts, what evidence is there that genetics are responsible for the smaller differences between blacks and whites?

    Why do you even need the hypothesis that intelligence differences between blacks and whites are due to genetics if non-genetic factors explain even larger differences within populations of blacks and whites? The Flynn Effect shows that non-genetic factors are larger than genetic ones.

    By what experimental technique are researchers distinguishing the non-genetic effects that the Flynn Effect shows are larger than the genetic effects that are hypothesized?

    Link to this
  8. 8. phalaris 2:30 am 05/31/2011

    daedalus2u : "There is no such thing as g that can be measured.": oh, so why don’t we all get to go to Harvard then?
    Excuse me, but aren’t you just playing with definitions (IQ, g, intelligence, SAT scores …)? Something is measured every time we take an exam, and the fact that higher education systems, on the whole, work indicates that it’s not entirely illusory. That "intelligence" covers a spectrum of traits doesn’t mean that none of these traits can be assessed with a useful level of accuracy.

    As for heritability: I suspect you appreciate the speciousness of your own arguments. Autism, for example, is known to be highly heritable, but the genetic basis of autism has turned out to be very tangled, and is still not fully clear, but no-one’s arguing against the unequivocal heritability evidence just because it’s not a single gene issue.

    For anyone who accepts Darwin, the assumption must be that traits corresponding to intelligence have a certain heritability, and the burden of proof should be with the deniers.
    Instead of which their tactics seem be to throw sand in the eyes the public.

    Link to this
  9. 9. denysYeo 5:27 am 05/31/2011

    In this article Zuberbuhler comments about human intelligence, not IQ. They are not the same thing!

    Link to this
  10. 10. daedalus2u 7:39 am 05/31/2011

    My argument is specious? My argument is that there isn’t data to support the claim that the differences in intelligence (however ill defined and poorly measured) between populations is due to differential genetics. The burden of proof is always with those making the assertion. Those who assert that differences in intelligence between individuals and groups is mostly due to differential genetics have the burden of proof to demonstrate that with actual data not simply by assertion.

    Heritable =/= coded by genes. MZ twins can be discordant for autism. Autism, like intelligence is a product of a phenotype, not a genotype. Genes don’t code for a phenotype, genes code for a process to make a phenotype.

    We know that the process of making a brain is complex and delicate. Numbers of in utero exposures interfere with that process. Maternal stress increases autism, as do some teratogens. Alcohol exposure causes fetal alcohol syndrome.

    If you want to actually address my argument, all you have to do is point me to where there is data that supports the idea that differential intelligence between individuals and populations is due to differential genetics. Not arguments based on incredulity, or popularity, or authority, or analogy, but actual data showing correlations between actual genes and intelligence test scores.

    If you can’t do that, at least have the intellectual honesty to admit that there isn’t data to support it and that the idea remains an untested hypothesis.

    Link to this
  11. 11. phalaris 1:36 pm 05/31/2011

    daedalus2u :
    From the wikipedia article on autism: "autism has a strong genetic basis".

    Wikipedia on "heritability of IQ" :
    "Estimates in the academic research of the heritability of IQ have varied from below 0.5[2] to a high of 0.9.[5] A 1996 statement by the American Psychological Association gave about .45 for children and about .75 during and after adolescence.[6] A 2004 meta-analysis of reports in Current Directions in Psychological Science gave an overall estimate of around .85 for 18-year-olds and older.[7] The New York Times Magazine has listed about three quarters as a figure held by the majority of studies.[8]"

    There are 58 references at the end of the article for you to peruse at your leisure.

    Is there a way I can reconcile these statements with your latest comments without coming to the conclusion that you, at best, are engaging in obfuscation and attrition?

    Link to this
  12. 12. Pugsley 4:51 pm 05/31/2011

    There is tons of data to show that one "population" on average has lower IQs than Asians or other "populations". You know that, Daedelus, and probably know that the average differences are very significant (about 15 pts). Perhaps you also know that the differences are present in all parts of the world (indicating genetic rather than cultural differences), and also show up in IQ tests designed by black psychometrists.

    As for specific genes being connected to it – that’s a tall order for polygenetic traits. That’s one of the things such research is about ….. of course it’s almost impossible to get govt grants for direct research into racial differences, so a lateral approach has to be found ….. but the OP is valuable for much more than that sort of thing.

    I admire the courage of scientists who research differences of intelligences between "populations", but they’re being naive if they think it will lead to a secure job and funding for grants. It’s probably best to leave that subject unstudied, too many people get pissed off by it, and few will learn anything from even the most undeniable findings.

    Link to this
  13. 13. jgrosay 5:54 pm 05/31/2011

    This kind of research gives entertainment and a way of living for the people that conducts it, but doesn’t add too much to the rest of mankind wellfare or health. Don’t need to say that humans and bonobos, the smartest of the chimps, although sharing 98% or more of genome, have enormous qualitative differences. Yes, we share the way of reproduction and some ways the hierarchy and social signalling is done, and some of this behavioural traits, inherited from a line of ancestors that goes back to worms and bacteria, are part of the bonds that keep society togheter and produces us some pleasures, but we are radically different. As long as we engage in animal connected activities, we enter dangers such as the ones depicted in Spike Lee’s "Jungle fever" movie, but that’s all, call it the reptile brain or the original sin. It must be clear that most of our activities are just games, played for fun, and don’t deserve to be raised to the consideration of philosophy. Salut +

    Link to this
  14. 14. jgrosay 6:22 pm 05/31/2011

    Intelligence in rats seems to be mainly inherited from the female parent, but in humans, environment has an important role,the contributions of Albert Einstein , for whom an IQ of 200 is suspected (Napoleon is given 140, and Sharon Stone scored 153 ), cannot be explained without the fact that he had an abnormal brain, his circumvolutions were different to that of others, some historical characters, such as Lenin and Nietzsche, were discovered to have suffered a military service time acquired disease, shyphilis, but the Einstein work probably will have had a worse result if he had not been educated in the german physics culture. Contributions of environment, from viruses, education, food to epigenetics must be taken into account.

    Link to this
  15. 15. daedalus2u 10:58 am 06/1/2011

    I didn’t ask for "expert opinions", I asked for data. I know that some "experts" claim there is a strong genetic component to autism but so far they have been unable to find what the genes are. They have no data to support their hypothesis of X%. Other researchers say there is a genetic component, but of unknown size. The most recent big GWAS:

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2947401/

    They said:

    "Our findings appear to rule out a common allele increasing relative risk by 2-fold or more. Much larger samples will be required to detect subtle effects on relative risk (e.g. 1.2), which is more typical of risk loci for common diseases."

    There is no theory as to how differential genetics would cause differential neurologically driven behaviors. The neurochemical basis of behaviors, the neuroanatomic basis of behaviors remain complete mysteries, just like the genetic basis of behaviors.

    In the wikipedia entry on heritability of IQ, didn’t you read the analogy, attributed to Richard Lewontin? Even Jensen agreed that it could be correct. The proponents of the idea that the differences in the measured IQ of populations is due to genetics don’t have data to support their idea, they just have the hypotheses.

    The Flynn Effect is known to be not due to genetics. If there are large differences between populations in the same ethnic group due to non-genetic effects why can’t the differences between between different ethnic groups be due to those same unknown but non-genetic factors too? There is no data that says it can’t be non-genetic differences and no data that says it is genetic.

    Link to this
  16. 16. phalaris 11:27 am 06/1/2011

    You are trying to confuse the issue by conflating mechanism with effect. You are blaming the researchers for not being able to explain how exactly the effect arises. But they don’t need a theory of mechanism to prove that a trait has a heritable component.

    Once again, is intelligence to a large extent adaptive? If so, how could it possibly have arisen if it is not heritable?

    Link to this
  17. 17. dubina 1:04 am 06/2/2011

    @daedalus2u

    I would point you to this.

    "Dr. Plomin has sought to move the debate forward by arguing that if genes for intelligence exist it should be possible to track some of them down through the powerful new genetic scanning techniques that have recently become available. Searching through a small part of the human genome, the long arm of chromosome 6, he found that a particular variant of a certain gene was twice as common in his sample of children with ultra-high IQ’s than in those with average IQ’s The gene has a very small effect, accounting for about 2 percent of the variance, or 4 IQ points, Dr. Plomin said."

    "The research, led by Robert Plomin of the Institute of Psychiatry in London, identified six genes that were strongly associated with high or low intelligence, but even the most powerful of these accounted for just 0.4 per cent of the variation in intelligence between individuals. The six together accounted for about 1 per cent of the variation in intelligence. Dozens of previous studies on twins and adopted children have established that about half of the variation in intelligence is down to environment."

    "Failing to find genes for intelligence has, in itself, been very instructive for Plomin. Twin studies continue to persuade him that the genes exist. “There is ultimately DNA variation responsible for it,” he says. But each of the variations detected so far only makes a tiny contribution to differences in intelligence. “I think nobody thought that the biggest effects would account for less than 1 percent,” Plomin points out.
    That means that there must be hundreds–perhaps thousands–of genes that together produce the full range of gene-based variation in intelligence."

    "The ultimate test of Plomin’s hypothesis will have to wait until scientists finally put together a list of genes that have an indisputable effect on how the brain works and that are associated with intelligence scores."

    Thus, genes and environments both factor intelligence, but in different ways. (Old news.) My sense of the issue here is that environmental factors are more subject to intervention and more important in practice. The path to mastery is influenced by genes, but has more environmental variance.

    Link to this
  18. 18. daedalus2u 3:20 pm 06/2/2011

    All I am faulting researchers for is making claims they can’t back up with data. They don’t know the mechanism for the Flynn Effect, but they do know it is not differential genetics.

    It makes no sense to attribute X% of intelligence to a certain gene. Intelligence is an emergent property of many genes and many environmental factors interacting in a non-linear and coupled ways over a lifetime. One of the most important periods is when the individual’s brain grows from a single cell to a brain with 10^11 cells.

    Using an X% model that assumes linearity when the system is highly non-linear is nonsense. The interactions are non-linear, they may well be non-monotonic depending on other genes, on other environmental influences, depending on lots of things which are unknown. In a non-linear and non-monotonic system a parameter can have a positive influence in one part of the parameter space and a negative influence in another. It is very likely that intelligence traits are non-monotonic because brain volume used for emotional intelligence can’t be used for mathematical (or any other type of) intelligence. There have to be trade-offs between the different functionalities that a brain of limited size can support. The brain is limited in size at birth by the size of the maternal pelvis. Brain volume used for sensory computations can’t be used for language or vice-versa. Those trade-offs in brain element volumes must also reflect brain element computational capabilities.

    In this (the most recent large study I could find, 7,900 individuals, and which is later than the one you quote from (I think))

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992848/

    Robert Plomin says:

    "Despite its three-stage design incorporating over 350,000 SNPs and its large sample size, our study has not identified strong associations between genetic variants and childhood general cognitive ability."

    When later and larger and better done studies fail to replicate earlier smaller studies, the likelihood that the earlier results were artifact increases. So far the big gene studies haven’t found any genes. They have ruled out that a few single genes have a large effect.

    Link to this
  19. 19. Mong H Tan, PhD 2:43 pm 06/3/2011

    RE: Absolutely not! — The scientific answer may lie in the "neocortical foundation" of our brain: whereby our "intelligence" is primarily accumulated and expressed by learning and communications — and not inherited or encoded in our "genes" as neo-Darwinists would have had persistently and reductively believed!?

    1) Why make it hard for science — especially neuroscience? I thought the problem has been that all neo-Darwinists, reductionists, and sophists worldwide, have had asked the wrong question; and thus they all have been pursuing in the wrong direction, especially concerning the "origin" of our human intelligence on Earth!

    Under the influence of this neo-Darwinist reductionism, Klaus Zuberbuhler and many pop-science readers herein and elsewhere, are no exception: such as this exemplary neo-Darwinist, self-obscurantist rhetoric and sophistry, as expressed above: "For anyone who accepts Darwin, the assumption must be that traits corresponding to intelligence have a certain heritability, and the burden of proof should be with the deniers. Instead of which their tactics seem be to throw sand in the eyes the public."

    2) However, historically, the great naturalist (not neurologist nor cell or molecular biologist nor geneticist) Charles Darwin’s theory of "natural selection" (NS) — not of "neurotransmitters" nor of "biomolecules" or "genes" — was intended not to be applied to "psychology" of his time (per Spencerism); nor applied to "genetics" a "heredity" subject (per Mendelism) that was totally unbeknownst to Darwin and his associates of their time, at all — as I have critically analyzed and argued in the "Psychiatric Times" before, and elsewhere, since June 2010 (please see a link here: http://www.searchmedica.com/search.html?useraction=search&d=us&ts=31052011&search.x=28&c=ps&search.y=6&parentreferrer=http://www.nature.com/news/2011/110223/full/news.2011.115.html&q=mong+h+tan&fr=true&ss=psychTimesLink&cid=smps-pt_search ). (To be continued below)

    Link to this
  20. 20. Mong H Tan, PhD 2:45 pm 06/3/2011

    RE: Absolutely not! (Continued from my comment 2 above)

    Whereas by applying Darwinism or the 1859 NS theory to the "population genetics" and "psychology" of the 20th century, the latter-day neo-Darwinists, reductionists, sophists, have had since the 1930s been stitching Darwinism and Mendelism uncritically and unscientifically together: as their then newfound "Modern Synthesis" (MS) or neo-Darwinism par excellence of the century!

    Subsequently, the concept of our human "genetics" and "psychology" have had also been reductively and rhetorically manufactured and synthesized (using more metaphors and analogies, of course) and single-handedly made extremely popular of the era by the then arising neo-Darwinist-reductionist extraordinaire, Richard Dawkins: who has had indeed made the concept of our genes and psychology to be his landmark pseudoscience theories of the "selfish gene" and "viral meme" of his then extremely pseudo-genetic and pseudo-linguistic lexicons and rhetoric, respectively and correspondingly established as those theories that have had been brilliantly and indelibly expressed in his 1976 bestseller book "The Selfish Gene" (please see "A metaphor too far" and my criticism in the Nature News online here: http://www.nature.com/news/2011/110223/full/news.2011.115.html#comment-id-18450 )!

    3) Consequently, just to paraphrase the neo-Darwinist obscurantism (in my comment 1) above: the public eyes have had indeed since been "blinded" by the "sand" of neo-Darwinism or MS; the pseudoscience sand, that has had been thrown and blown by neo-Darwinists and sophists alike worldwide since the mid-20th century!

    Even in the high academia today and worldwide, neo-Darwinism has had indeed become an occultism in Western philosophy — as neo-Darwinism has had again been morphed into an antireligious campaign: the "New Atheism" by Dawkins, et al (please see his 2006 exemplary book "The God Delusion") — and a self-obscurantism in science, especially "evolutionary biology" as I have recently observed and expressed here: http://www.nature.com/news/2011/110325/full/news.2011.187.html#comment-id-19559 a comment on "Frightened birds grow longer wings — RE: How neo-Darwinists, reductionists, have "darwinized" Mendelism (or genetics; since the 1930s); missed the current discovery of epigenetics in cell & molecular biology and biomedicine; and started to quarrel among themselves — in big time!" (NatureNewsUK; April 1). (To be continued below)

    Link to this
  21. 21. Mong H Tan, PhD 2:48 pm 06/3/2011

    RE: Absolutely not! (Continued from my comment 3 above)

    Nonetheless, by current definitions (since the 1980s) in our evolutionary and developmental neurobiology, neuropsychiatry, psychology, genetics, etc — but not the renowned neo-Darwinist, reductionist "geneticism" or the pseudo-linguistic "memetics" as frivolously created and propagated by Dawkins, et al (since the mid-1970s) — our intelligence (including our memory, creativity, and our refined or highly-evolved dexterity and bipedalism) has had been further initiated, acquired, communicated, and accumulated in the living neocortex of our brain (and not inherited or encoded in our genes); whereas the neocortex — one that comprises mostly our ruminating neurons — is clearly and phylogenetically in deficit: in most other animals and insects (social or otherwise)!

    Thus the comparative genomic studies in other primates may well turn out to be nothing but a foregone conclusion: That — biologically and phylogenetically — the neocortices in other mammals are just not too well-developed; or too well evolved "anthropogenetically" as those ruminating neurons, sprouting in our Homo sapiens lineage — specifically at a time when our homonid-ancestors had just begun to roam and explore on Earth: to seek foods; to discover, use, and control fire; to fashion stone tools and other utilities; to extract more natural resources; to create, transmit, and accumulate intelligence of their each respective cultures and survivorship; etc, etc, over 1-2 million years ago on this unique planet Earth!

    And, since the industrial revolutions worldwide since the turn of the 21st century, our global intelligence has further evolved and grown exponentially on Earth, and beyond, into the Universe and elsewhere (please see my seminal book "Gods, Genes, Conscience" especially Chapter 4: The Human Life, Mind, Dreams, Intelligence, and Conscience; linked below)!

    Best wishes, Mong 6/3/11usct1:48p; practical science-philosophy critic; author "Decoding Scientism" and "Consciousness & the Subconscious" (works in progress since July 2007), "Gods, Genes, Conscience" (iUniverse; 2006 — http://www.iuniverse.com/bookstore/book_detail.asp?isbn=0595379907 ) and "Gods, Genes, Conscience: Global Dialogues Now" (blogging avidly since 2006 — http://www2.blogger.com/profile/18303146609950569778 ).

    Link to this
  22. 22. gabriel_bear 5:24 pm 06/4/2011

    :"oh, so why don’t we all get to go to Harvard then? " evidently because so many cannot read darwin, who would only apply to the discussion if "adaptive" were inherent to intelligence. you fail to state this, and more importantly (according to darwin), adaptive to what environment.
    the act, sat, ceeb derive from the proposition (at harvard) that "what harvard desires" not that inheritable, and may in fact be deeply embedded in non-harvard families.
    and "what harvard desires" is by definition a cultural artifact, and not one from nature.

    Link to this
  23. 23. daedalus2u 1:55 pm 06/5/2011

    phalaris every aspect of the brain is adaptive. Sensory decoding is adaptive, sight, smell, touch, hearing, taste. All sensory decoding takes sensors and neuroanatomy to do the data processing. Voluntary movement takes neuroanatomy to generate the signals that move muscles. The autonomic nervous system is controlled by the brain too.

    Bloodhounds have a great sense of smell because they have a large number of sent detectors and a large olfactory cortex to decode those signals. However bloodhounds are considered one of the least intelligent dog breeds. This makes perfect sense. If more of the brain is utilized doing processing of smells, less is available to instantiate things like intelligence. Because there is a limit on brain size due to metabolic demand and genetics of skull size, there is a limit on how good any particular aspect of brain function can be compared to all others.

    In humans, the infant brain is limited in size at birth by the maternal pelvis. This limit on brain size has affected all human populations and all human ancestors since before humans speciated. In the absence of medical C-section, about 1% of mothers die per pregnancy due to cephalopelvic disproportion. Intelligence requires a large brain volume devoted to what ever intelligence requires. Increasing brain volume doesn’t only increase the brain functional capacity of the population, what it does is kill more mothers.

    There are many different volume elements in the brain. All of them are necessary to some extent. They can’t be reduced in size arbitrarily or the functions those volume elements instantiate will be lost. Someone without a visual cortex does have a greater skull volume that could be devoted to something else, but the brain is not perfectly plastic and volume cannot be reassigned so easily, and in "the wild", blind people don’t do so well, even if they are hyper-smart.

    Link to this
  24. 24. daedalus2u 2:08 pm 06/5/2011

    Most brain patterning happens in utero. The trade-offs between the thousands of different volume elements happens in utero, long before those volume elements come "online" and before their function can be evaluated. The trade-offs happen in utero because the "bottleneck" happens at birth. If the brain is too big at birth, mother and infant die.

    The maternal pelvis limit on brain size affects all functions of the brain, the dispersion in cognitive abilities of humans can be understood as trade-offs in different cognitive abilities. Better vision requires a bigger visual cortex, but a bigger visual cortex doesn’t show up as a higher "visual IQ" because IQ tests don’t measure that. They don’t measure "olfactory IQ", or "motor IQ", or "autonomic nervous system IQ", or any of the other thousands of things the brain does.

    In the absence of refrigeration, food preservation and good agricultural regulations, being able to tell which food was safe to eat via high "olfactory IQ" was a lot more important than it is today. People still die from eating food that is not safe to eat. Presumably a high "olfactory IQ" was even more important before things like refrigeration, the germ theory, and fire for cooking. Since humans were hunter-gatherers, a high "visual IQ" was important. Since humans hunted using thrown stones and sticks, a high "motor IQ" was important. Since humans listened to track prey, a high "acoustic IQ" was necessary too.

    Since everything that the brain does is "important", singling out one feature for evolution to maximize is an incorrect application of evolution. Because the cognitive abilities instantiated in a neural network are non-linear with network size, that is they vary approximately as n^2 rather than as n, a tribe that has dispersion among its members as to brain volumes allocated to various functions will do better than a tribe that has everyone "the same".

    In other words, a tribe with its members being geniuses at individual tasks will out-compete a tribe where everyone has average abilities. In other words, the tribe that can have its "high olfactory IQ" member identify spoiled food, its "high visual IQ" member gather, its "high motor IQ" member throw sharp sticks, its "high acoustic IQ" member identify when tigers are creeping up on the village will do better than the tribe where everyone has the same abilities.

    Link to this
  25. 25. daedalus2u 2:14 pm 06/5/2011

    Since the members of the tribe are all related, what evolution will select for is dispersion in mental abilities. If the dispersion in abilities occurred via discrete genes, a tribe of near related individuals sharing the same genes would all share the same abilities, the tribe would not have diverse abilities.

    Since the tribe with diverse abilities will out compete the tribe with monodispersed abilities, evolution will select for mechanisms that will cause dispersion in mental abilities independent of specific genes.

    Link to this

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