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37969Re: [evol-psych] Re: Re: IQ tests

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  • Fred Weizmann
    Sep 1, 2005
      As you indicate, Jerison specifically stated that his formula was not applicable to humans. However, that has not stopped people from using it in that way, often with misleading results. In a 1991 study Phil Rushton used a correction formula in a comparative study of Asian and non-Asian military recruits. Using this correction, Rushton found that the average cranial capacity of a sample of 24 large male samples of East Asian military recruits was 1460 ccs, compared with 1446 ccs for 20 comparable European military samples. However, as Reed and Jenson pointed out, the actual unweighted mean cranial capacity (unweighted because Rushton treated each sample as a single observation) for the Caucasian samples, prior to applying the corrected version of Jerison's formula, was actually larger than that of the East Asian samples.

      Rushton, J. P (1991) Mongoloid-Caucasian differences in brain race from military samples. Intelligence, 351-359.

      Reed, T. E., & Jenson, A. R. (1993). Cranial capacity. New Caucasian data and comments on Rushton's claimed Mongoloid-Caucasoid brain size differences. Intelligence, 407-422.

      Fredric Weizmann

      Jason Malloy wrote:
        Julian O'Dea: Why must there always be an adjustment for 
      body size?  I have never understood the force of this argument. 
      Larger is larger, isn't it?  
      The distinction has proved meaningful in the evolutionary study 
      of intelligence between absolute brain size and EQ 
      (encephalization quotient) which is a measure of brain size over 
      and above what is predicted from body size (or what is 
      considered needed for basic "house-keeping"). The 
      assumptions pan out rather well. Harry Jerison's 'Evolution of the 
      Brain and Intelligence' is still a classic:
      That's for between-species comparisons. Now within-species, 
      or at least within the human species this doesn't appear to be 
      the case (but again the IQ/brainsize correlation in humans may 
      be spurious). Here are statements from the 'Handbook of 
      Human Intelligence':
      "Brain size is not related to body size in humans"
      pg 241 chapter 11. H. Jerison
      "contrary to what is sometimes claimed, no study of brain 
      volume (or head size) has shown a substantial decrement in 
      correlation after partialling out either height or weight (or both)"
      pg 246 chapter 12. P. Vernon et al
        As for the intelligence of Homo floresiensis, as I pointed out 
      at the annual meeting of the Australasian Society for Human 
      Biology last year, parrots and other birds are proving to be 
      surprisingly intelligent despite their small brain size.  
      Presumably it is a matter of efficient packaging.
      No birds have small bodies, and homo floresiensis has a very 
      low EQ. Here's Richard Dawkins:
      "Biologists expect small animals to have small brains anyway 
      and they have developed ways of calculating this. The EQ or 
      Encephalisation Quotient is a measure of how much bigger (or 
      smaller) a brain is than it "ought to be" for its body size, given that 
      it is, say, a mammal. 
      Calculated in this way, modern humans have an EQ of about 6, 
      meaning that our brain is six times as big as it "ought to be" for a 
      mammal of our size. Homo erectus is believed to have an EQ of 
      about 4, and Australopithecus (our probable ancestors of about 
      3m years ago) about 2.5 or 3 (similar to a modern chimpanzee). 
      Flores woman comes into the same range as Australopithecus 
      or modern chimpanzees. "
      So Flores has tools like an erectus but is encephalized like a 
      chimp or Lucy. As for birds, EQ matters, as a big study that just 
      came out this year shows:
      "They gathered data on brain mass for 1,967 species.
      In more than 600 introductions of nearly 200 bird species into
      new habitat they found that species with brains large relative to
      their body size tended to survive better in new environments than
      smaller-brained birds.
      Examples include the introduction in the 19th century of the
      European starling to North America.
      "Overall, our results provide strong evidence for the hypothesis
      that enlarged brains function, and hence may have evolved, to
      deal with changes in the environment," they wrote in this week's
      issue of the Proceedings of the National Academy of Sciences.
      The researchers last month published an IQ index guide to birds
      that show corvids — birds from the crow family including ravens
      and jays — are by far the cleverest birds.
      Next on the list are hawks, woodpeckers and herons, while
      partridges, new world quails, emus and ostriches are the dolts
      of the bird world."
      This study is interesting because it added external validity to 
      animal intelligence tests (similar in content to human 
      intelligence tests) which also showed a connection between bird 
      species performance and EQ (same for primates). 
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