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Heritabilities of fitness traits

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  • Joao Sousa
    Jussi Nielema: ... If g is a fitness character , as Jensen suggests, it should have at least a low narrow-sense heritability (h2n). Evolutionary textbooks
    Message 1 of 8 , Apr 2, 2006
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      Jussi Nielema:

      At 12:41 01-04-2006 +0300, you wrote:
      >2006/4/1, Joao Sousa <j.d.sousa@...>:
      >
      > > Of course. Also the relatively high heritability of g itself, as measured
      > > within a population, doesn't favour the idea that average g of a population
      > > is an adaptation - for adaptations should have zero or small heritabilities
      > > (0 - 0.15), after relevant evolution has operated for many generations.
      >
      >I don't agree with Joao Sousa: there's always variation in polygenic
      >traits (like g), evolution wouldn't be possible without it (no
      >differences in alleles = no genic selection). I think there's plenty
      >of good arguments for g's adaptiveness in the EEA. On the other hand,
      >Irwin is probably right saying g isn't so adaptive in modern
      >environment (less offspring for high IQ people). This of course has
      >something to do with contraceptives and healthcare. The same goes for
      >high status individuals: in modern societies their reproduction
      >success is often poor compared to low status individuals. However, IMO
      >Linda Gottfredson's theory of the evolution of g is promising because
      >it explains how important it has been in the EEA.
      >
      >Here's Arthur Jensen's argument on the evolutionary importance of g
      >from his synopsis of the The g Factor:
      >
      >37. Traits that show genetic dominance provide evidence that they have
      >been subjected to natural selection as a Darwinian fitness character
      >over the course of evolution. IQ, and particularly its g component,
      >manifest the theoretically predictable effects of genetic dominance:
      >inbreeding depression in the offspring of consanguineous parents, and
      >the opposite effect, hybrid vigor (or heterosis), that shows up in the
      >offspring when each parent has a different racial ancestry. Tests'
      >relative g loadings significantly predict the degree to which various
      >tests manifest both inbreeding depression and heterosis. These data
      >support the hypothesis that the g factor of psychometric tests has
      >arisen through natural selection over the course of human evolution
      >and therefore can be regarded as a fitness character in the Darwinian
      >sense.

      If g is a "fitness character", as Jensen suggests, it should have at least
      a low narrow-sense heritability (h2n). Evolutionary textbooks show tables
      with many traits and h2n is usually below 0.2 for traits more directly
      related to fitness. From a table in Futuyma book (p.252), the h2n was 0.01
      - 0.2 for the following traits: conception rate, litter size, egg
      production, viability (in cattle, pigs, sheep, chickens, mice, drosophila),
      and it was 0.3 - 0.95 for other traits such as colors, body length, tail
      length, thorax length, bristle numbers, and so on.

      Maynard Smith too, shows some data on this and states (p.118) that h2n
      tends to be small for more fitness-related traits. Still, that's true that
      some h2n is kept even in these traits, because of i) recurrent deleterious
      mutations; ii) these fitness traits may be negatively correlated with one
      another (e.g. egg size and egg number; or longevity and fecundity) because
      of constraints; iii) also cycles between parasites and hosts contribute to
      a chronic state of directional evolution promoting some substantial
      heritabilities, as Hamilton studied so well. However, the fact is that the
      measured h2n for these important traits tend to be small.

      Heritability estimates obtained in the social sciences should have a
      substantial part of non-additive genetic variance (and thus be somewhere
      between h2n, and h2b - the broad sense heritability). If the heritability
      of g is so high, as Jensen says (he says h2b is 0.60 - 0.70 in adults),
      then likely the narrow sense heritability, h2n, is probably higher than
      0.20. If so, Jensen's claim that it is a fitness trait is at odds with what
      mainstream evolutionists say about fitness traits.

      Since I'm citing these books I seize the opportunity to recall that these
      authors had a very negative opinion about IQ studies, the g concept, and
      theories on racial differences in IQ. Futuyma expresses his critiques in
      p.747-749 of the same book. Maynard Smith expressed it in other writings. I
      have read the same sceptic commentaries, usually 2 to 4 pages long, in many
      other authors, including R.Boyd and J.Silk, Matt Ridley, Michael Cummings,
      and many others I don't have in memory now. These are the finest evolutionists.

      Some listmembers may think that the only ones who object to race realist
      views are the biologically-illiterate PCs, and the traditional critics,
      Gould, Lewontin, Rose, Kamin. That's not true.



      Boyd R & Silk J (1997) How Humans Evolved, NY: WW Norton

      Cummings M (2000) Human Heredity, Pacific Grove: Brooks/Cole

      Futuyma D (1998) Evolutionary Biology, 3rd ed, Sunderland Mass: Sinauer

      Maynard Smith J (1998) Evolutionary Genetics, 2nd ed, Oxford: OUP

      Ridley Matt (1999) Genome, London: Fourth Estate
    • J.K. Niemelä
      Whatever you say, the heritability of g is about 70% and this has been shown repeatedly, empirically. You seem to think that Arthur Jensen is the only
      Message 2 of 8 , Apr 2, 2006
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        Whatever you say, the heritability of g is about 70% and this has been
        shown repeatedly, empirically. You seem to think that Arthur Jensen is
        the only scientist who says this, but the heritability he mentions is
        what we call a scientific fact.

        <snip>

        "1. Individuals differ in intelligence due to differences in both
        their environments and genetic heritage. Heritability estimates range
        from 0.4 to 0.8 (on a scale from 0 to 1), most thereby indicating that
        genetics plays a bigger role than does environment in creating IQ
        differences among individuals. (Heritability is the squared
        correlation of phenotype with genotype.) If all environments were to
        become equal for everyone, heritability would rise to 100% because all
        remaining differences in IQ would necessarily be genetic in origin. "

        Here's a list of the scientists who accept this view:

        - Richard D. Arvey, University of Minnesota
        - Thomas J. Bouchard, Jr., University of Minnesota
        - John B. Carroll, Un. of North Carolina at Chapel Hill
        - Raymond B. Cattell, University of Hawaii
        - David B. Cohen, University of Texas at Austin
        - Rene V. Dawis, University of Minnesota
        - Douglas K. Detterman, Case Western Reserve Un.
        - Marvin Dunnette, University of Minnesota
        - Hans Eysenck, University of London
        - Jack Feldman, Georgia Institute of Technology
        - Edwin A. Fleishman, George Mason University
        - Grover C. Gilmore, Case Western Reserve University
        - Robert A. Gordon, Johns Hopkins University
        - Linda S. Gottfredson, University of Delaware
        - Robert L. Greene, Case Western Reserve University
        - Richard J.Haier, University of Callifornia at Irvine
        - Garrett Hardin, University of California at Berkeley
        - Robert Hogan, University of Tulsa
        - Joseph M. Horn, University of Texas at Austin
        - Lloyd G. Humphreys, University of Illinois at Urbana-Champaign
        - John E. Hunter, Michigan State University
        - Seymour W. Itzkoff, Smith College
        - Douglas N. Jackson, Un. of Western Ontario
        - James J. Jenkins, University of South Florida
        - Arthur R. Jensen, University of California at Berkeley
        - Alan S. Kaufman, University of Alabama
        - Nadeen L. Kaufman, California School of Professional Psychology at San Diego
        - Timothy Z. Keith, Alfred University
        - Nadine Lambert, University of California at Berkeley
        - John C. Loehlin, University of Texas at Austin
        - David Lubinski, Iowa State University
        - David T. Lykken, University of Minnesota
        - Richard Lynn, University of Ulster at Coleraine
        - Paul E. Meehl, University of Minnesota
        - R. Travis Osborne, University of Georgia
        - Robert Perloff, University of Pittsburgh
        - Robert Plomin, Institute of Psychiatry, London
        - Cecil R. Reynolds, Texas A & M University
        - David C. Rowe, University of Arizona
        - J. Philippe Rushton, Un. of Western Ontario
        - Vincent Sarich, University of California at Berkeley
        - Sandra Scarr, University of Virginia
        - Frank L. Schmidt, University of Iowa
        - Lyle F. Schoenfeldt, Texas A & M University
        - James C. Sharf, George Washington University
        - Herman Spitz, former director E.R. Johnstone Training and Research
        Center, Bordentown, N.J.
        - Julian C. Stanley, Johns Hopkins University
        - Del Thiessen, University of Texas at Austin
        - Lee A. Thompson, Case Western Reserve University
        - Robert M. Thorndike, Western Washington Un.
        - Philip Anthony Vernon, Un. of Western Ontario
        - Lee Willerman, University of Texas at Austin

        Please see http://www.udel.edu/educ/gottfredson/reprints/1997mainstream.pdf

        Add to this the researchers on the APA Task Force (minus those who are
        already mentioned above), who state:

        <snip>

        "Across the ordinary range of environments in modern Western
        societies, a sizable part of the variation in intelligence test scores
        is associated with genetic differences among individuals. Quantitative
        estimates vary from one study to another, because many are based on
        small or selective samples. If one simply combines all available
        correlations in a single analysis, the heritability (h2) works out to
        about .50 and the between-family variance (c2) to about .25 (e.g.,
        Chipuer, Rovine, & Plomin, 1990; Loehlin, 1989). These overall figures
        are misleading, however, because most of the relevant studies have
        been done with children. We now know that the heritability of IQ
        changes with age: h2 goes up and c2 goes down from infancy to
        adulthood (McCartney, Harris, & Bernieri, 1990; McGue, Bouchard,
        Iacono, & Lykken, 1993). In childhood h2 and C2 for IQ are of the
        order of .45 and .35; by late adolescence h2 is around .75 and c2 is
        quite low (zero in some studies). Substantial environmental variance
        remains, but it primarily reflects within-family rather than
        between-family differences."

        The scientists who accept this view are:

        Ulric Neisser, PhD, Chair; Emory University
        Gwyneth Boodoo, PhD, Educational Testing Service
        Thomas J. Bouchard, Jr., PhD, University of Minnesota
        A. Wade Boykin, PhD, Howard University
        Nathan Brody, PhD, Wesleyan University
        Stephen J. Ceci, PhD, Cornell University
        Diane F. Halpern, PhD, California State University, San Bernadino
        John C. Loehlin, PhD, University of Texas, Austin
        Robert Perloff, PhD, University of Pittsburgh
        Robert J. Sternberg, PhD, Yale University
        Susana Urbina, PhD, University of North Florida

        These facts about the heritability of g are also mentioned in two
        major textbooks of sociobiology, Social Evolution by Robert Trivers
        (1985, p. 99-102) and Animal Behavior - An Evolutionary Approach by
        John Alcock (7th Ed., 2001, p. 57-8). The latest edition of Alcock
        (8th, p. 69-70) is a bit more PC on IQ, but nevertheless the data is
        there.

        There's always variation in polygenic traits like g:

        http://www.ndsu.nodak.edu/instruct/mcclean/plsc431/quantgen/qgen2.htm

        <snip>

        "The above graph shows the distribution of the data in the above
        table. This graph has the bell-shaped curve that is indicative of the
        normal distribution. This has important implications for the manner in
        which quantitative traits are analyzed."

        This example demonstrates additive gene action. This means that each
        allele has a speicific value that it contributes to the final
        phenotype. Therefore, each genotypes has a slightly different metric
        or quantitative value that results in a distribution (or curve) of
        metric values that is similar approach a continuous curve.

        Other genetic interactions such as dominance or epistasis also affect
        the phenotype. For example, if dominant gene action controls a trait,
        than the homozygous dominant and heterozygote will have the same
        phenotypic value. Therefore, the number of phenotypes is less than for
        additive gene action. Furthermore, the number of phenotypes that
        result from a specific genotype will be reduced further if epistatic
        interactions between several loci affects the phenotype. Additive,
        dominance, and epistatic effects can all contribute to the phenotype
        of a quantitative trait, but generally additive interactions are the
        most important.

        -----

        Add to this assortative mating, which for IQ is substantial, "with
        average spouse correlations of about .40..." (Plomin et al.:
        Behavioral Genetics, 4th Ed., 2001, p. 170), and what you have is even
        more variance in a population.

        As to the fitness value of g, here's once again Richard Dawkins' propositions:

        1. There was a time when our ancestors were less brainy than we are.

        2. Therefore there has been an increase in braininess in our ancestral lineage.

        3. That increase came about through evolution, probably propelled by
        natural selection.

        4. Whether propelled by selection or not, at least part of the
        evolutionary change in phenotype reflected an underlying genetic
        change: allele replacement took place and consequently mean mental
        ability increased over generations.

        5. By definition therefore, at least in the past, there must have been
        significant genetic variation in braininess within the human
        population. Some people were genetically clever in comparison with
        their contemporaries, others were genetically relatively stupid.

        Source: Extended Phenotype (Revised Edition 1999), p.26.

        BTW, Matt Ridley's Genome has S.J. Gould's The Mismeasure of Man in
        the references and reading suggestions. Indeed, you instanly notice
        the influence of Gould in Ridley's text. Ridley's latest book Nature
        via Nurture is much better on g, so probably he has done what Steven
        Pinker has done, i.e. delved deeper into the matter and in the face of
        the facts, relinquished his political correctness.


        BW,
        Jussi
        --
        Those who can make you believe absurdities can make you commit
        atrocities. - Voltaire
      • Jim Mackintosh
        Perhaps a better model for the heritability of IQ to consider is the heritability of height in humans because i) it involves humans; ii) is clearly polygenic;
        Message 3 of 8 , Apr 3, 2006
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          Perhaps a better model for the heritability of IQ to consider is the
          heritability of height in humans because i) it involves humans; ii) is
          clearly polygenic; iii) appears to have undergone a recent level of
          directional selection.

          Most research articles generally record the heritability of height in
          humans around 0.5, or around 0.8 if the sexes are partitioned out. I
          think you would agree that is not a contentious finding.

          Yet clearly human populations do vary in their average height. Therefore
          if it were shown that average height were an adaptation, then in
          principle average g can also be an adaptation with high heritability.

          Jim Mackintosh



          Joao Sousa wrote:

          >If g is a "fitness character", as Jensen suggests, it should have at least
          >a low narrow-sense heritability (h2n). Evolutionary textbooks show tables
          >with many traits and h2n is usually below 0.2 for traits more directly
          >related to fitness. From a table in Futuyma book (p.252), the h2n was 0.01
          >- 0.2 for the following traits: conception rate, litter size, egg
          >production, viability (in cattle, pigs, sheep, chickens, mice, drosophila),
          >and it was 0.3 - 0.95 for other traits such as colors, body length, tail
          >length, thorax length, bristle numbers, and so on.
          >
          >Maynard Smith too, shows some data on this and states (p.118) that h2n
          >tends to be small for more fitness-related traits. Still, that's true that
          >some h2n is kept even in these traits, because of i) recurrent deleterious
          >mutations; ii) these fitness traits may be negatively correlated with one
          >another (e.g. egg size and egg number; or longevity and fecundity) because
          >of constraints; iii) also cycles between parasites and hosts contribute to
          >a chronic state of directional evolution promoting some substantial
          >heritabilities, as Hamilton studied so well. However, the fact is that the
          >measured h2n for these important traits tend to be small.
          >
          >Heritability estimates obtained in the social sciences should have a
          >substantial part of non-additive genetic variance (and thus be somewhere
          >between h2n, and h2b - the broad sense heritability). If the heritability
          >of g is so high, as Jensen says (he says h2b is 0.60 - 0.70 in adults),
          >then likely the narrow sense heritability, h2n, is probably higher than
          >0.20. If so, Jensen's claim that it is a fitness trait is at odds with what
          >mainstream evolutionists say about fitness traits.
          >
          >Since I'm citing these books I seize the opportunity to recall that these
          >authors had a very negative opinion about IQ studies, the g concept, and
          >theories on racial differences in IQ. Futuyma expresses his critiques in
          >p.747-749 of the same book. Maynard Smith expressed it in other writings. I
          >have read the same sceptic commentaries, usually 2 to 4 pages long, in many
          >other authors, including R.Boyd and J.Silk, Matt Ridley, Michael Cummings,
          >and many others I don't have in memory now. These are the finest evolutionists.
          >
          >Some listmembers may think that the only ones who object to race realist
          >views are the biologically-illiterate PCs, and the traditional critics,
          >Gould, Lewontin, Rose, Kamin. That's not true.
          >
          >
          >
          >Boyd R & Silk J (1997) How Humans Evolved, NY: WW Norton
          >
          >Cummings M (2000) Human Heredity, Pacific Grove: Brooks/Cole
          >
          >Futuyma D (1998) Evolutionary Biology, 3rd ed, Sunderland Mass: Sinauer
          >
          >Maynard Smith J (1998) Evolutionary Genetics, 2nd ed, Oxford: OUP
          >
          >Ridley Matt (1999) Genome, London: Fourth Estate
          >
          >
          >
        • Joao Sousa
          ... Height is not a fitness trait. Like arm size, bristle number in flies, and IQ, and so on, it shows heritabilities so high because selection is not very
          Message 4 of 8 , Apr 3, 2006
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            At 18:28 03-04-2006 +1000, you wrote:
            >Perhaps a better model for the heritability of IQ to consider is the
            >heritability of height in humans because i) it involves humans; ii) is
            >clearly polygenic; iii) appears to have undergone a recent level of
            >directional selection.
            >
            >Most research articles generally record the heritability of height in
            >humans around 0.5, or around 0.8 if the sexes are partitioned out. I think
            >you would agree that is not a contentious finding.
            >
            >Yet clearly human populations do vary in their average height. Therefore
            >if it were shown that average height were an adaptation, then in principle
            >average g can also be an adaptation with high heritability.
            >
            >Jim Mackintosh

            Height is not a fitness trait. Like arm size, bristle number in flies, and
            IQ, and so on, it shows heritabilities so high because selection is not
            very stringent on height. For the fitness traits, h2n is around 0 - 0.2. As
            for its status as an adaptation, there are several definitions of
            adaptation. My take is that if, for example, a population has average
            height = 1.5 m, but variation is high and heritability is high too, hardly
            the height = 1.5 m should be called an adaptation, because the high
            heritability means that individuals far from the mean are having
            substantial reproductive success.

            Jussi:
            Whatever you say, the heritability of g is about 70% and this has been
            shown repeatedly, empirically. You seem to think that Arthur Jensen is
            the only scientist who says this, but the heritability he mentions is
            what we call a scientific fact.

            I didnt disagree on that, just that such heritability is hardly compatible
            with g being a fitness trait.
          • Irwin Silverman
            On Mon, 3 Apr 2006, J.K. Niemelä wrote: Individuals differ in intelligence due to differences in both ... That is not an accurate statement, no matter how
            Message 5 of 8 , Apr 3, 2006
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              On Mon, 3 Apr 2006, J.K. Niemelä wrote:

              Individuals differ in intelligence due to differences in both
              > their environments and genetic heritage. Heritability estimates range
              > from 0.4 to 0.8 (on a scale from 0 to 1), most thereby indicating that
              > genetics plays a bigger role than does environment in creating IQ
              > differences among individuals. (Heritability is the squared
              > correlation of phenotype with genotype.) If all environments were to
              > become equal for everyone, heritability would rise to 100% because all
              > remaining differences in IQ would necessarily be genetic in origin. "
              >
              > Here's a list of the scientists who accept this view:

              That is not an accurate statement, no matter how many accept it.
              The correct statement is, "Heritability estimates range
              from 0.4 to 0.8 ... indicating that genetic DIFFERENCES play a bigger
              role than do environmental DIFFERENCES in creating IQ differences among
              individuals." As heritability estimates are calculated, this is a function
              of the magnitude of genetic vs. environmental differences in the sample.
              Thus, when the sample is environmentally homogeneous, heritability is high,
              and visa versa. The best estimate, then, would be based on a meta-analysis
              of data across a variety of samples, which yields an estimate of about .50
              (.52, when I last looked)
              Notwithstanding the above, the question remains of the relationship
              of heritability estimates to the relative roles of genetics and environment
              in the ontogeny of I.Q. itself. This will probably prove to be impossible to
              quantify in any significant manner, based on the multitude and complexity of
              interactions that are involved. Take Piaget's theory of intelligence, for
              example, which is based on a series of critical periods in maturation for
              the acquisition of various cognitive capacities. How would you quantify
              the contribution of genetics in laying down the critical periods or the
              contribution of environment in providing the supports?
            • H.M. Hubey
              Like the previous post in which it is claimed that natural selection selects for average intelligence, this one says that height has nothing to do with
              Message 6 of 8 , Apr 3, 2006
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                Like the previous post in which it is claimed that natural selection
                selects for average intelligence,
                this one says that height has nothing to do with selection.

                If it is claimed that this is true in the present, no problem. If the
                claim is that it was always
                so, then how did humans become more intelligent than chimps and how did
                they get
                tall. Apparently among our ancestors were very short ones.



                Joao Sousa wrote:
                >
                > Height is not a fitness trait. Like arm size, bristle number in flies, and
                > IQ, and so on, it shows heritabilities so high because selection is not
                > very stringent on height.
                >
              • J.K. Niemelä
                2006/4/3, Irwin Silverman : How would you quantify ... Pretty tough questions! The proximate how questions are of course very important - and
                Message 7 of 8 , Apr 3, 2006
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                  2006/4/3, Irwin Silverman <isilv@...>:

                  How would you quantify
                  > the contribution of genetics in laying down the critical periods or the
                  > contribution of environment in providing the supports?

                  Pretty tough questions! The proximate "how" questions are of course
                  very important - and they indeed are the future of behavioural
                  genetics (Plomin et al., 2001, p. 319 et passim). However, I don't see
                  these questions relevant to our current discussion. Indeed, there's
                  something familiar in them.

                  Here's a quiz show question. Who wrote the following, where and when?

                  "This expression describes another confused notion: the idea that
                  unless we can know absolutely EVERYTHING about the genetics of
                  intelligence we can know nothing! Proponents of this view demand that
                  we be able to spell out in detail every single link in the chain of
                  causality from genes (or DNA molecules) to test scores if we are to
                  say anything about the heritability of intelligence. Determining the
                  heritability of a characteristic does not at all depend upon a
                  knowledge of its physical, biochemical, or physiological basis or of
                  the precise mechanisms through which the characteristic is modified by
                  the environment. Knowledge of these factors is, of course, important
                  in its own right, but we need not have such knowledge to establish the
                  genetic basis of the characteristic. Selective breeding was practiced
                  fruitfully for centuries before anything at all was known of
                  chromosomes and genes, and the science of quantitative genetics upon
                  which the estimation of heritability depends has proven its value
                  independently of advances in biochemical and physiological genetics."

                  Answer:

                  The quote is from Arthur Jensen's notorious HER article How Much Can
                  We Boost IQ and Scholastic Achievement? (1969). The title of that
                  section is "Know All versus know Nothing". Not much have changed after
                  all these years, as far as the criticisms of the heritability of g are
                  concerned.

                  Well, luckily the discussion has now moved towards the evolution of g,
                  which I think was our original subject.

                  BW,
                  Jussi

                  --
                  Those who can make you believe absurdities can make you commit
                  atrocities. - Voltaire
                • Irwin Silverman
                  ... If we are promoting the idea that heritability numbers are quantitative indices of the relative contributions of heredity vs enviroment to the development
                  Message 8 of 8 , Apr 4, 2006
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                    On Tue, 4 Apr 2006, J.K. Niemelä wrote:

                    > 2006/4/3, Irwin Silverman <isilv@...>:
                    >
                    > How would you quantify
                    > > the contribution of genetics in laying down the critical periods or the
                    > > contribution of environment in providing the supports?
                    >
                    > Pretty tough questions! The proximate "how" questions are of course
                    > very important - and they indeed are the future of behavioural
                    > genetics (Plomin et al., 2001, p. 319 et passim). However, I don't see
                    > these questions relevant to our current discussion. Indeed, there's
                    > something familiar in them.

                    If we are promoting the idea that heritability numbers are
                    quantitative indices of the relative contributions of heredity vs
                    enviroment to the development of g, I would think there is a great
                    deal of relevance in the argument that we do not know much of anything
                    about the development of g.
                    Think about it this way. When we do learn the answers to the
                    "proximate" questions (if they are quantifiable) we may have a whole new
                    set of figures.




                    Irwin Silverman, Ph.D.
                    Psychology Department
                    York University
                    4700 Keele Street
                    Toronto, Ontario
                    Canada
                    M3J 1P3

                    Office: (416) 736-5115 x66213
                    Fax: (416) 736-5814
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