Saturday, October 20, 2007

Is There a Genetic Component to "Intelligence"?

 
This is not my field and, quite frankly, I don't really care about any differences or similarities in intelligence between different human demes. However, the recent kerfuffle over the intemperate remarks of a Jim Watson have raised a number of interesting issues. One of these is whether there is a genetic component to intelligence.

I have always thought there was. I remember reading Richard Dawkins' take on this subject some years ago. He pointed out that if the average "intelligence" of humans has increased over the past million years by evolution then it follows logically that there were genes (alleles) for differences in intelligence that were selected. It seems unreasonable to imagine that all the alleles have reached fixation so that in today's 7 billion members of the Homo sapiens species there is no genetic variation for "intelligence." (I'm putting "intelligence" in quotation marks because I don't want to get into protracted battles about how to measure it or even how to define it. Let's just agree that there's something called intelligence that exists.)

Up until now I have been under the impression that certain genetic defects resulted in lowered intelligence. For example, Down's Syndrome is strongly correlated with low scores on an IQ test suggesting that the presence of extra chromosome 21 genes affects intelligence. That's a genetic component of intelligence by most reasonable definitions.

In spite of evidence to the contrary, there seem to be a number of people who deny that there's a genetic component to intelligence. One of these is Greg Laden, whose opinion I greatly respect. In a recent posting [Watson’s Lecture Canceled] he even disputes the twin studies that show a strong correlation between intelligence and heritability.
Heritability does not distinguish in and of itself between traits passed on with genes from traits passed on via culture, learning, environment, and so on. For instance, which language a person speaks has a very high heritability value, but this “trait” is entirely, 100% learned with absolutely no genetic component whatsoever. Twin studies have been used to suggest that IQ has a component of heritability that is genetic since it is more correlated in twins than in, say, full sibs. However, non-genetic traits can follow the same pattern. Non-genetic traits can show this pattern because, with respect to environments, full sibs who are not twins do not share the same environment as twins. (And for other reasons.)
It seems to me that Greg is arguing against a genetic component to intelligence. He seems to be going out of his way to discredit any studies that suggest otherwise. I'm not sure where he's coming from on this and that's the reason for posing the question in this posting.

Later on in the comments section of Greg's article he says the following.
We have, on this site anyway, not discussed the fact that neural development in humans does not really allow for much influence from genetics in the way that is asserted by the Rushtonian race argument; we have seen some discussion that the allegations that intelligence = g = IQ = something measurable in a simple way = something that varies across individuals because of allelic differences in some set of genes. But there are a LOT of reasons to not accept this idea, aside from the major disconnect between the genome and the functioning of the brain owing to the actual way real brains actually develop in real life. There has been very little discussion regarding the disconnect between the concept of heritability and the concept of subspecies in animals (race is simply another term for subspecies).

There are so many levels at which this is so wrong that I can’t help but feel … and I’ve said this already … that the Race Concept and the intelligence piece of this are simply not valid scientific arguments, and are almost always either political arguments or arguments being made from ignorance. They are political in their motivation, because the science here is simply operating in a totally different place (a little place I call reality).
Clear as mud. I fully sympathize with the mixture of politics and science that confuses this issue. There are people who want there to be differences in intelligence between races because it fits with their political agenda.

I wonder if there aren't people who believe the opposite because it fits with their political agenda? I wonder if there aren't people who go out of their way to construct pseudo-scientific arguments denying that there can be a genetic component to intelligence. Why would they do this? Because if there's no genetic component to intelligence then there can be no differences between demes and this avoids a messy political debate.

Frankly, I'm not sure if Greg Laden is doing this so I'd like to see some clarification. Is there a genetic component to intelligence? Are there "intelligence" alleles segregating within the human population such that some people are smarter than others because of their parents and not just because of socioeconomic environment? Or, are all differences in intelligence due to environment?

Please, let's not let this thread degenerate into a discussion about racism. Let's talk about the science and stick to the question.



54 comments :

  1. I would certainly follow you as far as you have gone here: what you have said seems reasoned, unbiased, and open to reasonable pursuasion.

    ReplyDelete
  2. Putting aside the issue of race, what about genetic differences in intelligence between individuals in general?

    Surely Laden is not suggesting that all differences in intelligence between individuals are accounted for by exclusively environmental factors?

    If you agree that intelligence is a property of the brain - which is obviously a part of the body - how is it that, as distinct from the rest of the body which shows clear genetically-determined differences, there is no genetic variability present in the brain amongst humans at all? This just doesn't make any sense. At the very least it's an extraordinary claim that requires extraordinary evidence to support it.

    Now, dividing people up based on race may very well be a silly idea for all sorts of reasons, but that's a different question to the one I am asking here. Are there people who genuinely believe that the human brain is not subject to genetic variability?

    ReplyDelete
  3. I'd be very suprised if there wasn't some some genetic component to intelligence.

    Lets do a Darwin and look at artificial selection first, in dogs. Some breeds of dogs are recognised as being intelligent, and some breeds (lovable though they may be) are pretty dumb. The same applies to other domesticated animals.

    Lets look at humans. Some demes can digest cows milk when adult. Several different genetic changes have been found to enable this trait in different demes.

    Similarly populations native to the Tibetan and Andean plateaux have both adapted to prolonged high altitude life - but by different genetic changes.

    Although I recognise that the definition of "intelligence" is loose, it seems to me that local selection pressures could be just as effective in changing this trait as any other. Indeed if "intelligence" was proved to be the same throughout the various human demes I would expect a special explanation as to why "intelligence" was exempt from selection.

    Denying the possibility for political reasons, no matter how well intended, is just poor science.

    ReplyDelete
  4. Larry:

    Funny you should mention this. I was just composing a post on this issue, but I don't think it will be on my site until Monday.

    It would actually take me more time and work to explain how the political and social side of this affects my opinion (or not). I'll stick to the science.

    Yes, in some way, at some level, there has to be genetic variation. But human intelligence is not necessarily a polygenic trait affected by genes with numerous alleles. There are a number of traits that exist with very simple genetic changes that are structural. What we know about neural development in humans compared to apes most strongly suggests a small number of developmental (control) changes as constituting the evolutionary shift in terms of genetics.

    At the same time there are myriad genes involved in proper functioning. These may look like "intelligence" or "grammar" or "langauge" or "whatever" genes because when they break so does some neural function. But this does not mean that there are or were multiple alternative alleles that were under selection.

    Any genetic or evolutionary model for intelligence needs to jive with the developmental process we know occurs in the brain. The result of this important and strong guideline is that the usual models (allelic variation selected over time) are no good.

    I write more on my site about this later, but I assure you, this is a large and complex issue! (As you know.)

    ReplyDelete
  5. Ian ... if you look at how neural systems work, the claim that neural systems develop in a way that allows for the allelic variation model (with racial sorting or not) is actually the claim that is extraordinary.

    The model you are working with and would like to see the neural/intelligence fit into is itself a bit of a straw-man model to begin with.

    Discovered: Again, you are using inappropriate models. You could probably get a dog-breed effect by breeding humans, by finding individuals with broken genes, mating them, and getting them to breed true over time. That does not have much to do with the evolution of intelligence or the neural development in humans.

    ReplyDelete
  6. Intelligence must have at least some heritable genetic basis, or it couldn't have evolved. The real question is how it is inherited, and whether or not it can be correlated with race to any significant degree. Maybe the genetic precursors are very complex, and not easily divied up into racial categories, with many exceptions and special cases. Based on my personal experience, I would say that's probably likely. I've seen some very intelligent people of mostly African descent.

    BTW, I think the biases in this regard are not so much political, but personal. People want some scientific justification that they are somehow better than others, or in a higher "class". Very few people have the ability to view themselves with absolute honesty.

    ReplyDelete
  7. Regarding the heritability of intelligence, I found this post about experimental and statistical flaws in the separated twin studies interesting. I don't have the statistics to judge the arguments but I at least came away with the impression that, whatever the truth of the matter, you need to be cautious in trusting that data.

    ReplyDelete
  8. I think that there must be some genetic component to intelligence, but I think that the variation within human populations is probaly drowned out by environmental factors; especially fetal and infant nutrition, exposure to alcohol and other toxins in utero and the presence (or absence) of an enriched and literate environment during early childhood.

    Add in personal temperament, quality of education, stability of family life, exposure to different ways of thinking and cultures, etc... and you more than make up for any small divergence between inate IQ levels.

    ReplyDelete
  9. Careful about twin studies, they are very often fudged. Read Lewontin about that.

    Despite any conceptual disagreements, I think we can all agree that the hypothesis of genetic determinism of IQ must eventually "materialize" into the discussion of REAL, molecular genes.

    Take microcephalin. If you don't have this gene, you have a very small brain and don't survive (correct me if there is survival). There are many variations of these genes in "survivors", but it does NOT correlate with IQ.

    Microcephalin is obviously an essential genetic component of IQ. But this does not maena that variations in the microcephalin genes are responsible for differences of IQ in the population.
    Genes are necessary, but not sufficient, to develop IQ. (This is no surprise to the neurobiologist, who knows that we learn even the way that we see, in interaction with the environment).

    The interesting thing would be a gene whose presence were sufficient to establish an increase in IQ tests. Right?

    Now, for thosse who really know about the importace of the environment in the development of brains, it is clear that the environement will more often drown out these genetic differences.

    ReplyDelete
  10. I shall read Greg's post with interest - but if the human brain structure is developmentally channeled and a myriad of genes which affect the functioning of the brain may not have multiple alleles, why do we observe so much variation in "intelligence" within existing demes?

    I think I can see the points that Greg is making, but they have to explain observed differences between individuals, intelligent parents having (on average) intelligent kids, and changes in brain structure and volume over evolutionary time.

    ReplyDelete
  11. Genetic contribution to inter-individual differences in intelligence does not necessarily imply that there are racial (demic) differences in the distribution of genetic potential for intelligence.

    Consider height. Inter-individual differences in height have a genetic component. Also, there are marked population differences in height. Yet, studies of immigration and economic change show that different populations have remarkable similarity in genetic potential for height. (Besides a few "pygmy" groups.) So while genes contribute to height differences, and populations differ in height, gene differences are not responsible for these population differences. (Except for "pygmies.") Height potential is roughly the same across races, while manifested height differs due to differences in diet, disease, and other developmental stress.

    Why would we expect similarities in genetic potential for intelligence across races?

    One, I suspect that the potential human intelligence is deeply genetically-ontogenetically conserved and robust, related to a series of major regulatory changes in brain development that gave rise to erectus-grade and later archaic sapiens Homo. (No, not hopeful monster macromutations.) This developmental program is relatively robust and can facilitate mutations and insults with compensatory mechanisms to produce rough functional equivalence. A profoundly disruptive mutation results in nonviability or severe impairment. Thus, most non-pathological genetic variants will have minor or insignificant effect on intelligence, and even these will be buffered by the brain developmental system. Human brain development involves somatic selection mechanisms to coordinate brain growth and structure with the body and social and ecological environment. (See Deacon, Purves, Edelman, Hull...) (Admittedly, some of this is speculative, but it's theoretically and empirically grounded.)

    Two, as some have pointed out, the main selective force driving and maintaining intelligence was not the physical environment (which is roughly equivalently challenging in various global ecosystems in any case) but the Red Queen effect of competing and cooperating with other minds - related models known as Social IQ, Machiavellian intelligence, Gossip Hypothesis, 'Mating Mind.' This community of language-using minds produces a universally uniform selective environment across populations. The main constraint to brain size is pelvic, which is locomotory and also universal. The weak size-IQ link, inter-individual variability brain size shows, and the lack of an upward trend in brain size over the last half million years indicates that selection is not responsible for normal brain size differences. "Racial" differences in brain size and shape are mainly due to Bergman's rule of globularity in higher latitudes.

    More reason to believe that races have roughly equivalent potential for intelligence:

    1) Modern Homo sapiens has been around for about 200,000 years but civilization (intensive agriculture and the state) is only a few thousand years old.

    2) Human languages are equally structurally complex.

    3) Africa's Kushite states prove early and advanced civilizational capacity in black Africans.

    Tupaia

    ReplyDelete
  12. In contrast to the developmental conservation, constraint, and robusticity of human brain development, traits in which there are marked population and "racial" differences in distribution tend to be developmentally deconstrained and often rapidly evolving. Traits such as digestive enzymes, pigmentation, facial skeleton robusticity (like pigmentation, a neural crest feature), and immune variants.

    Tupaia

    ReplyDelete
  13. I think intelligence has several components. The heritable part is capacity, all humans have a similar capacity, but so do dogs and so do cats. I don't agree that brain size really makes the difference I think structure does, elephants may have a larger brain mass but the brain structure doesn't give them the ability to do Physics. Another component is health - environment, diet, and cleanliness all play into overall health. Then there is exposure to information - education.

    People from disadvantaged countries generally have the same capacity but loose in health and exposure to information. It is easy for the eugenicists to point at them and claim lowered intelligence. I know many people who don't have a higher education but who are very intelligent. George Bush is an example of someone who is educated but not very intelligent.

    ReplyDelete
  14. Heritability is the proportion of variation in a population that is due to differences in genotypes. The notion of heritability is hard to understand properly. These hypothetical examples might help clarify it. Consider them gedanken examples.
    1) Suppose there is a population that has genetic variation for height and, further, that there is no environmental contribution to height -- height depends solely on the genes an individuaal inherits. Any differences in height between individuals in this population are then due to genetic differences. The heritability of height in this hypothetical population is 100%. All the variance in height is due to genetic variation.
    2) Now assume that a nutritional supplement is discovered that will add 10 inches to the height of an individual. If we feed every individual in population 1, above, the same amount of supplement, the average height will increase by 10 inches. But the heritability will still be 100% because all the differences in height are still due to genetic differences.

    Heritability does not tell us if a trait can (or cannot) be changed by changing the environment. It only describes the proportion of variance in a trait due to differences in genotypes, within the population under study, including the environments that population is exposed to.

    For that reason you cannot apply a heritability estimate derived from one population to another one. The other population will have a different set of genotypes and a different set of environments. Furthermore, knowledge of heritability does not enable you to predict how a population will respond to a change in the set of environments.

    You also can't use heritability to estimate the importance of the environment to the development of a trait in an individual. It measures the contribution of heredity and environment to differences between individuals, not within an individual. So if the heritability of height is 80% that does not mean that 80% of your height was determined by your genotype and 20% by your diet. It only means that 80% of the differences between individuals in your population can be attributed to differences in their genotypes.

    (Note that I am simplifying the notion of heritability here -- there are really two heritability concepts, broad sense and narrow sense, but that is another story.)

    ReplyDelete
  15. From a post on Dienekes' Anthropology Blog in defense of Watson:

    http://dienekes.blogspot.com/2007/10/on-james-watson-black-iq-controversy.html

    "the identification of intelligence-fostering genes differentiating populations has not come about yet. The prudent stance is to be agnostic about this issue, until such genes are discovered, or their continued non-discovery makes one doubtful of their existence."

    Given that record of non-discovery, the question then becomes: How many failures to find genes that distinguish the cognitive potential of races need we observe before we conclude that such differences are unlikely to ever be found - because they don't exist?

    Sanders mentioned microcephalin. "Race realists" gloated that the geographic distribution of variants in that gene was ironclad proof that they had finally been vindicated. That triumphalism crumbled late last year when the racialist hypothesis for microcephalin was falsified. (In addition, microcephalin was even related to Europe's Upper Paleolithic, which recent archaeological evidence has shown was not quite so abrupt and unprecedented after all.)

    At some point we have to stop being evenhanded and say, "No, it isn't undecided; the hypothesis of racial differences in intelligence potential is simply unsupported."

    Some will disagree on whether we are at that point yet, but inevitably, if the pattern of negative evidence holds, we will be.

    Tupaia

    ReplyDelete
  16. You're debating this without Flynn?

    Pete Dunkelberg

    ReplyDelete
  17. How many failures to find genes that distinguish the cognitive potential of races need we observe before we conclude that such differences are unlikely to ever be found - because they don't exist?

    it's worth keeping in mind that the genetic basis of things like skin and eye color have only started to be understood in the last couple years (see here and here for skin color, and here for eye color). It's indisputable that these things are largely genetic, and that the differences between populations in phenotype are due to differences in allele frequencies at the genotype level. They're relatively "simple" genetic traits, yet again, the responsible genes have only been identified within the last couple years.

    Genetic variants influencing "intelligence" (following Dr. Moran, I'll put it in quotes, and it's obvious the environment influences it as well) have not been searched for nor found. Yet they will, and likely soon.

    Watson was not nearly as nuanced as they should have been, but his basic hypothesis--that the alleles influencing intelligence have different frequencies in different continents--is testable, and will be tested once those variants are found. Patience.

    ReplyDelete
  18. I don't think that anyone disputes that there is a genetic component to intelligence; after all I can study all that I want and I'll never be like Pearlman. :-)

    The question is whether there are intelligence difference between groups of people, and whether such measured differences are due to social factors (poverty, discrimination, class/status) or genetics.

    After all, Australian aboriginals are genetically not similar to Africans at all, and yet they have a gap between them and the non-aboriginal population that is bigger than the IQ gap between African Americans and white Americans.

    If I am not mistaken, the same IQ difference holds true for Turks in Germany and the non-Turkish Germans.

    ReplyDelete
  19. > after all I can study all that I want and I'll never be like Pearlman.

    I've been with smart people, and I can't keep up, I have to work-work-work for what seems to come easily to others--so yes, some folks have innate ability in this area, I would say it's probably genetic to some degree.

    > The question is whether there are intelligence difference between groups of people...

    Exactly, that there are innate abilities in intelligence, and differences in ability, I think is plain, whether this is true between races, I think is likely untrue--at the very least agnosticism is in order.

    ReplyDelete
  20. Intelligence is something that is deep-seated in our genes and our humanity - like walking upright. And it probably goes back just as far. The basis for intelligence and walking upright were both forged in our genome long before the races in homo sapiens began to diverge.

    ReplyDelete
  21. Intelligence is something that is deep-seated in our genes and our humanity - like walking upright. And it probably goes back just as far.

    Australopithecines like Lucy walked upright, and had more or less chimp brains.

    ReplyDelete
  22. anonymous says,

    Genetic contribution to inter-individual differences in intelligence does not necessarily imply that there are racial (demic) differences in the distribution of genetic potential for intelligence.

    I don't understand why you say this. If there are multiple alleles for intelligence segregating in the population then it's practically impossible for two different demes to have exactly the same frequency of these alleles according to my understanding of population genetics and evolution.

    In my opinion, once you've identified variability then it follows automatically that different subgroups will differ in that characteristic. You can quibble over the extent and the significance of the difference but to deny that there can ever be a difference strikes me as total nonsense.

    ReplyDelete
  23. Larry Moran: "it's practically impossible for two different demes to have exactly the same frequency of these alleles".

    I should have written "marked differences." (What does "marked" mean? I'll have to think about that some more.) But more importantly, note my phrasing: "racial (demic) differences in the distribution of genetic potential for intelligence."

    I quite intentionally did not write "gene frequencies." "Genetic potential for intelligence" says nothing about allele frequencies.

    It only means that we should expect that genetic substrate of intelligence to provide for highly similar distributions in intelligence across populations. Some genes, and especially gene combinations, will be functionally equivalent in regard to "intelligence" ("g") to others within the context of the developmental system of the human brain. Perhaps specific morphological parameters or cognitive functions will differ, yet generalized "intelligence" will be the same.

    Think of the brain-mind as a hierarchical network of dynamic processes: genome, epigenome, cell activities, cellular assemblies, higher order information processing functions, and finally, highest order abstract properties like "intelligence." A system like that will be robust with multiple buffering and redundancies, as well as difficult-to-predict sensitivities to perturbation. Variation in allele frequencies will ramify through that system in a highly complex manner. Hence numerous functional rough equivalences in various processes.

    Tupaia

    ReplyDelete
  24. Note: In the third paragraph, by "cognitive functions" I mean allelic variation hypothetically contributing to variation in specific tasks such as, for example, verbal recall, spatial rotation, attention shift and the like. Even with these, however, factors like hormones, stress, illness, diet, environmental richness and other developmental and lifespan factors will have large impacts in determining the performance of these tasks.

    Tupaia

    ReplyDelete
  25. "genetic substrate of intelligence to provide for highly similar distributions in intelligence across populations."

    Not that I am referring to all else being equal; that is, given similar environments, including prenatal. (I'm trying to think of ways in which my words will be misinterpreted.)

    The brain developmental system I am describing is both fairly genetically canalized and highly environmentally sensitive. The brain achieves this by being a self-organizing, allostatic, selectionist system, the state of which depends on the body, environment, and its own history of activity.

    Tupaia

    ReplyDelete
  26. I think there is no question that a genetic component makes "intelligence" possible, but the mutations in these genes have big-scale deficiencies like down syndrome or having a miniaturized brain. I think this means genes act at a very essential and basic level but does not relate directly to the later development that affects IQ, even if it makes it posible. Necessary; but not sufficient.

    Now if we are going to say in any meaningful way that the differences of IQ among "normal" people are determined by differences in genetic composition, we INDEED are implying that genes, rather than the environment, are resposible for phenotypic differences (an absurd in the light of the evidence, but whatever). That is, the genes must be powerful enough to have a reliable effect on the phenotype (IQ), REGARDLESS of environmental-educational differences. They must be "sufficient" to consistently produce an increase in IQ.
    We still don't know of any gene that is sufficient to produce a notable increase in IQ, all argued cases have small effects and rely on mere ststistically significant correlation, that is, having the gene will not always produce an increase in IQ

    ReplyDelete
  27. BTW, those who know me perhaps can imagine the chuckles I get over this argument that "if it evolved....it is genetic"

    ReplyDelete
  28. It might be a mistake to assume that 'intelligence', however you measure it, should be equated with genetic fitness. Is high intelligence the best strategy in every environment? Clearly very low intelligence is not conducive to independent survival but average or slightly below average intelligence frequently correlates with higher numbers of offspring. Certainly this may be a question of environment (poverty, low education levels etc) but genetic factors DO play a part in at least a proportion of cases - such as in female fragile X carriers who often have both low IQ levels and have large numbers of children. This has nothing to do with race but it at least indicates the possibility that genes that affect intelligence levels can exert effects that might lead to an increase in the allele frequency in particular environments (in this case it is the modern universal healthcare post germ theory environment that allows virtually all children to survive infancy).

    ReplyDelete
  29. Before going into this issue ... the related developmental biology, genetics, etc., I wanted to work out on paper some of the reasons why I may approach this whole problem differently than some.

    If you grow up in a world in which it is presumed that whites are superior to blacks, then how do you address the issue of race scientifically and objectively? Alternatively, if you adopt the politically motivated belief or the religious belief that "all people are created equal" or "all people are the same" or whatever, then again, how do you address the question objectively?

    This is a bit of a red herring, because there is not one perspective versus another that is either free from or affected by subjectivity or bias.

    However, one thing that someone can do is to be self-reflective about one's experience, presuppositions, etc. I've done this over the years in a number of fora, but never on this blog.

    To correct this error of omission, I've written this:

    http://gregladen.com/wordpress/?p=1559

    ReplyDelete
  30. Here's an abstract on presciptive information in biopolymers-DNA. Its really the leading edge in science...

    Peer-reviewed and accepted July 2006
    Physics of Life Reviews

    Self-organization vs. self-ordering events in life-origin models

    by David Abel and Jack Trevors

    Self-ordering phenomena should not be confused with self-organization. Self-ordering events occur spontaneously according to natural "law" propensities and are purely physicodynamic. Crystallization and the spontaneously forming dissipative structures of Prigogine are examples of self-ordering. Self-ordering phenomena involve no decision nodes, no dynamically-inert configurable switches, no logic gates, no steering toward algorithmic success or "computational halting".

    Hypercycles, genetic and evolutionary algorithms, neural nets, and cellular automata have not been shown to self-organize spontaneously into nontrivial functions. Laws and fractals are both compression algorithms containing minimal complexity and information. Organization typically contains large quantities of prescriptive information. Prescriptive information either instructs or directly produces nontrivial optimized algorithmic function at its destination. Prescription requires choice contingency rather than chance contingency or necessity. Organization
    requires prescription, and is abstract, conceptual, formal, and algorithmic. Organization utilizes a sign/symbol/token system to represent many configurable switch settings. Physical switch settings allow instantiation of nonphysical selections for function into physicality. Switch settings represent choices at successive decision nodes that integrate circuits and instantiate cooperative management into conceptual physical systems. Switch positions must be freely selectable to function as logic gates. Switches must be set according to rules, not laws. Inanimacy cannot "organize" itself. Inanimacy can only self-order. "Self-organization" is without empirical and prediction-fulfilling support. No falsifiable theory of self-organization exists. "Self-organization" provides no mechanism and offers no detailed verifiable explanatory power. Care should be taken not to use the term "self-organization" erroneously to refer to low-informational, natural-process, self-ordering events, especially when discussing genetic information.

    Platolives

    ReplyDelete
  31. When folks aren't tremendously knowledgeable about a topic, they tend to oversimplify. I usually find this blog on the side of the thorough, complex answer. This time, I fear the discussion is headed toward oversimplification.

    To counteract that tendency, let me highly recommend two posts on "intelligence" and the measurability and inheritability thereof, from Cosma Shalizi's very fine blog, which can be found at http://www.cscs.umich.edu/~crshalizi/weblog/ . The dates of the posts are October 18 (earlier of the two posts of that date), and September 27th.

    ReplyDelete
  32. martinc says,

    It might be a mistake to assume that 'intelligence', however you measure it, should be equated with genetic fitness.

    I agree. If there were strong selection for intelligence then people would be a lot smarter than they are. (Assuming, of course, that there is a genetic component to intelligence.)

    I suspect there might have been selection for increases in intelligence in the past.

    ReplyDelete
  33. jud says,

    When folks aren't tremendously knowledgeable about a topic, they tend to oversimplify. I usually find this blog on the side of the thorough, complex answer. This time, I fear the discussion is headed toward oversimplification.

    Sometimes there are people who make simple things complicated in over to avoid unpleasant implications. The reference you pointed us to does exactly that.

    We all know about the difficulties with IQ tests. But don't let those difficulties blind us to the possibility that there's a genetic component to intelligence. That's what Cosma Shalizi is doing. The arguments are convoluted and almost impossible to follow. I strongly suspect that this obfuscation is motivated by an honest desire to promote peace and harmony between blacks and whites but bias is bias no matter how pure your motives.

    ReplyDelete
  34. sanders says,

    BTW, those who know me perhaps can imagine the chuckles I get over this argument that "if it evolved....it is genetic"

    I'm glad you're enjoying the discussion. I certainly get lots of chuckles over your comments.

    BTW, the definition of evolution that I use is "Evolution is a process that results in heritable changes in a population spread over many generations." [What Is Evolution?]. Perhaps you could tell us your definition?

    ReplyDelete
  35. sanders says,

    Now if we are going to say in any meaningful way that the differences of IQ among "normal" people are determined by differences in genetic composition, we INDEED are implying that genes, rather than the environment, are resposible for phenotypic differences (an absurd in the light of the evidence, but whatever). That is, the genes must be powerful enough to have a reliable effect on the phenotype (IQ), REGARDLESS of environmental-educational differences. They must be "sufficient" to consistently produce an increase in IQ.

    I don't know if you're deliberately trying to mislead us or if you really think that the genetic component of intelligence has to trump environment all the time.

    I'll assume ignorance, rather than maliciousness.

    When you're dealing with an imprecise variable like intelligence it's difficult to sort out the nature vs. nurture contributions. We all know that differences in scores on IQ tests can easily be due to environment so that someone whose genes should give them an advantage can be outscored by someone who has an advantage in environment.

    I hope you understand this and I hope you appreciate that the rest of us do as well.

    I believe that there's a genetic component to intelligence such that given exactly the same environment some people will be more intelligent than others because of the genes they inherit from their parents.

    Sanders, do you believe that some breeds of dogs are more intelligent than others or are those perceived differences all due to environment? Do you believe that Albert Einstein was no smarter than all the rest of us—he just had a good upbringing?

    ReplyDelete
  36. Certainly larry, you need to update yourself on the role of non-genetic change in evolution. The fact that any trait has evolved does not mena thta it has doen so involving ony genetic changes.
    I'll leave it there, since the literature about the evolutionary relevance of non-genetic change is abundant enough already. You've got homework.

    ReplyDelete
  37. Larry, I am simply pointing out to the fact that the mutations for intelligence are big-sclae downwards shifts, never upwards.
    Think about the relation of thsi observation to the experimental evidence for the riole of learning in the development of the brain.
    I am not saying there is NO influence of genes on IQ variations among "normal" people; I'm saying that the EVIDENCE until know suggests that it is negligible. So YEAH, i you experiment, if environmentla conditions were absolutely equal, there could be some miserable differences in IQ.

    Other thn that I am demanding somethign perfectly logical: traits are suposed to be "inheritable" and "geetic" when they come up regardless of environment. OR do you think that peopel with Down syndrome can somehow environmentally avoid their conditon? Only so far. the gentic alteration makes its contribution, o matter what. In fact to say in any significant way that intelligence is genetic, the intelliegence genes must be able to make a contribution, even if slight, with independence from the environment. We know sverla genes that are like this; but no genes like this that just make people smarter.

    What happens is that this trait is simpy not heavily determined by genes, which is what I've been saying all along....

    ReplyDelete
  38. Tupaia says,

    It only means that we should expect that genetic substrate of intelligence to provide for highly similar distributions in intelligence across populations. Some genes, and especially gene combinations, will be functionally equivalent in regard to "intelligence" ("g") to others within the context of the developmental system of the human brain. Perhaps specific morphological parameters or cognitive functions will differ, yet generalized "intelligence" will be the same.

    We have a situation where there are distinct differences in intelligence between individuals within a deme. These within-deme differences have to be due to a number of alleles that are segregating within a population.

    But somehow there's a special buffering system that prevents allele differences between demes, right?

    How, exactly does this work? When one of the alleles in a given deme drops in frequency—say by random genetic drift—is there some kind of signal sent to the other deme to make an adjustment? :-)

    Do you see the problem? As long as there are differences between individuals then it follows that these difference are due to differences in allele frequencies. (Assuming a genetic component.)

    This means that there are a finite number of alleles segregating within the population. As long as that's the case then it's practically impossible for any two demes to have exactly the same frequency of alleles.

    Hence, if there's a genetic component to intelligence then different demes will almost certainly differ in the distribution of the phenotype manifest by the intelligence alleles.

    The only way to avoid this unpleasant conclusion is to advocate that there is no genetic component to intelligence and everyone has exactly the same potential to be as smart as Albert Einstein or as stupid as Paris Hilton.

    ReplyDelete
  39. I agree with your defintion but I'd prefer to concentrate on phenotypic, organismic changes rather than populational; and I would be careful to understand that the environment is part of inheritance (repetition of a phenotype). That is inheritance=genes is not true.

    ReplyDelete
  40. Do you believe that Albert Einstein was no smarter than all the rest of us—he just had a good upbringing?

    It all depends on what you mean by "smart". Would Einstein have been a champion chess-player? A top business executive? An artistic genius? Intelligence and mental ability can take many forms.

    From what I've read, he had some difficulty in school, and was only "intelligent" in subjects that interested him. Certainly he was a unique thinker and "well-adapted" to survive in a university physics environment, but outside of his domain in physics, was he really that much smarter than the rest of us? Was he a universal genius? (if there is such a thing).

    ReplyDelete
  41. BTW, larry, about your dogs comment, do you have any idea what domestication and artificial selection usually do to "IQ"?
    How dramatic do you think are the differences within the original wild dog?

    ReplyDelete
  42. einstein was way better than simply "smart" (as defiend by IQ scores)
    he was creative and an independent thinker

    ReplyDelete
  43. do you think einstein would have com up with raltivity if he was born the hilton heiress, Larry?
    cheesy rhetoric is easy

    ReplyDelete
  44. Different combinations of alleles could well result in functionally equivalent reaction norms for "intelligence." A key part of my argument is that selective forces involved in intelligence are roughly uniform between human populations due to the primary selection pressure being other human minds in a kind of Red Queen effect (limited by universal constraints, including pelvic dimension).

    Within populations, frequency-dependent selection for a continuum of ecological strategies maintains a degree of genetic variation in intelligence potential. However, most variation in intelligence within populations is nongenetic and due to developmental plasticity.

    One reason why different allelic combinations can result in functional equivalence is because the brain is genetically canalized (though I would not go as far as Greg Laden or Sanders) yet environmentally sensitive. This is due in part to somatic selection process within the brain.

    Here is an example of a clear group difference in brain development-linked genes and hormones, brain morphology (white vs gray matter, corpus callosum), brain size (both absolute and relative), and specific information processesing tasks (e.g. object rotation) - yet resulting in roughly equivalent intelligence: men and women. While male intelligence distribution has more variance, with greater representation in both the upper and lower ends, the means are about the same.

    Nongenetic inheritance: Without getting into redefinitions of evolution, this is of particular interest in regard to the human brain. Uterine environment, epigenetic inheritance, maternal immunoglobins, maternal pathogens, modeled behaviors, symbolic-linguistic transmission, and constructed environment are crucial to the generation of differential outcomes in intelligence.

    ----------------

    General references for this discussion:

    Loci involved in neurodevelopmental disorders (not normal variation)
    http://www.nature.com/nrg/journal/v7/n1/fig_tab/nrg1747_T1.html

    The search for QTLs in intelligence
    http://www.scq.ubc.ca/?p=292

    review of The Gene Illusion
    http://www.human-nature.com/nibbs/03/jjoseph.html

    Tupaia

    ReplyDelete
  45. From what I've read, he had some difficulty in school, and was only "intelligent" in subjects that interested him. Certainly he was a unique thinker and "well-adapted" to survive in a university physics environment, but outside of his domain in physics, was he really that much smarter than the rest of us? Was he a universal genius? (if there is such a thing).

    Einstein was no slouch. If you read Abraham Pais definitive scientific biography 'Subtle is the Lord...' The Science and the Life of Albert Einstein you never the less get insight into Einstein's skills in other areas. The related 'difficulties' seems to be an urban legend, Einstein did very well but wasn't interested in excelling in areas outside physics.

    He had certainly a knack for both philosophy (arguing with Bohr about the basis for quantum physics) as well as engineering (co-inventing a series of gas-absorption refrigerators (ie without moving parts and silent) with Leó Szilárd. (Admittedly, Einstein may have only helped with the paperwork as he had been a patent clerk. Then again, that is a certain skill set as well.)

    At the time of Einstein it was already too late to be a universal genius, as science had expanded much. I think you have to go back to Gauss to find the latest such.

    ReplyDelete
  46. Another thing you may want to go over, Larry, is what Lewontin says about how different reaction norms for different genotypes have radically different shapes, and are not simply higher and higher curves, piled one over the other, as is assumed if you want to argue that some people could just "genetically better" at learning than others, despite the fact that the environment affects the trait. Such an arrangement is almost never found in real biology, when we do controlled measurements with organisms of the reaction norms for diferent environmentally sensitive traits.

    Compare figure 1.6 vs figure 1.8 in Lewotin's "triple helix" book.

    ReplyDelete
  47. One more comment from me, people often underestimate the tremendous complexity of language, but it is indeed remarkably difficult to analyze (say) with computer programs.

    Now this extraordinary ability for language, extraordinary in and of itself, is present in all groups of people, and so this can show how an extraordinary ability can be present in all groups--where also some in each group do not have facility in language.

    Now some do have unusual ability in this area, and may become philologists, or know a dozen languages or more, but the point remains that a remarkable ability--though most might think it unremarkable--is present across the board.

    ReplyDelete
  48. I think it is incorrect to presume that any extraordinary ability is due to some genetic cause (the "evolutionary psychology" perspective of genotype=phenotype). Life history can explain many abilities, motivations...

    I am willing to make bets with anyone, that training for IQ tests produces an increase many times that ever argued to be produced by an "intelligence gene".

    I think we already have the evidence that differences in environment are much greater than genetically produced differences. So if I were asked if I endorsed an eugenics program for improving intelligence, no. It would be ineffective. Although I have no doubt they would succeed selecting "downwards", toward dumb. That's where all the big effect genes are.
    To elevate IQ scores, my recommendation would be to focus on EDUCATION.

    ReplyDelete
  49. An analogy of how different alleles and physiological differences could result in differences in a global metric like "intelligence":

    Consider height. It seems simple and straightforward. But think of its components. Start with lengths of body segments, including leg length and trunk length. Given a certain height, if trunk length is as shorter as leg length is longer, the outcome - height - will be the same. Now consider the physiological components: insulin receptors, calcium metabolism, cytokines involved in osteoblast proliferation, thyroxine binding proteins and so on. Finally, there are the alleles of the various loci that affect these processes. Variants in some can result in the same outcomes if there are corresponding differences in others, just like leg length and trunk length can vary and produce the same outcomes - as long as these changes are compensatory. Therefore, different populations can have different allele frequencies for the multiple loci involved in height yet have similar height distributions.

    The genes is unit of selection, but the individual is the level of selection. Selection operates not on alleles, but on traits (in the context of an organism, so-called "interactors") - which impacts allele frequencies. If selection is the primary determinant of allele frequencies in large populations within a species, then similar selective environments will give rise to similar phenotypic outcomes even if allele frequencies vary between populations.

    If drift is more important in determining alleles involved in brain function then this not necessarily the case. Certainly the frequency of alleles involved in neutral phenotypic variants is determined by drift. But intelligence is not selectively neutral. Drift could also have a strong influence on non-neutral variants in small, isolated populations. However, while neutral and even some non-neutral variants were largely determined by drift, intelligence is unlikely to be among them.

    Tupaia

    ReplyDelete
  50. "An analogy of how different alleles and physiological differences could result in differences in a global metric like "intelligence""

    I meant to write "result in similarities," - the opposite - as in similar distributions between populations.

    Tupaia

    ReplyDelete
  51. The human brain obviously has a potential to be used far beyond what it may actually end up being used. There is a spark of truth in these affirmations that we use "only a small percentage" of our brain. After all, small kids can loose substantial portions of their brain tissue and still develop normal cognitivie abilities.
    Remember how Wallace was so impressed a savage could learn to sing or play sophisticated western music, despite he would never face that challenge in the jungle?
    There is a fairly interesting case, I think 1920's, of 2 girls raised by wolves rescued in india which includes some photographs of the girls running on all fours. I remeber they said they never were able to train them to walk at all times bipedal and they only learned a few words.

    I think the human brain is similar to the lung or to the liver, where you have way more alveoli or cells than you will probably ever use in your live. It is a hypertrophied organ; but that does not mean it will actually get used.

    Note that "overadaptations", like neutral and negative traits, also escape from the easy logic of the adaptationist

    ReplyDelete
  52. Wait, people were actually raised by wolves? I thought that was a figure of speech derived from Romulus/Remus stories and such.

    ReplyDelete
  53. No, the case of Amala and Kamala is actually pretty well documented.

    http://niewyjasnione_zjawiska.w.interia.pl/muzyka/146t.jpg

    ReplyDelete
  54. Based on my personal experience, I would say that's probably likely. I've seen some very intelligent people of mostly African descent.

    ReplyDelete