…But not the same size

(re: Nisbett (2007). All brains are the same color)

When it comes to the issue of population differences in intelligence, the average differences in cranial capacity are an important piece of evidence. Whatever their ultimate cause (i.e., whether due to environmental differences or genetic differences that resulted from environmental differences), they establish the deep rootedness and biologicality of (some of the) global GMA differences. There is, naturally, a good deal of resistance to this conclusion, which is reflected in the fraudulent discussions of cranial variation in many anthropological texts.

For example, In Chapter 5, Regional Variation and Evolution, of their textbook, Human Lineage, Cartmill and Smith (2009) authoritatively state:

While correctly noting the population differences in CC/brain size (see: Appendix A in Smith and Beals 1990 and table 2 in Beals et al., 1984), they claim that the differences are unrelated to differences in intelligence. In making their case, they cite chapter 5, The Size of intelligence: A gross misunderstanding, of Deacon (1997), The symbolic species: the co-evolution of language and the brain

In the cited chapter, Deacon, in fact, does not discuss intrahuman variation in intelligence or brain size. Rather, he argues, as the title of the chapters suggests, that bigger brains did not make humans smarter than other primates. (Cf. Reader (2011); Table 4. The relationship between primate general intelligence and brain volume).

In their discussion, Cartmill and Smith not only misrepresent Deacon’s chapter but, having brought up the issue, neglect to inform the readers about the copious amount of evidence that has accumulated internationally since the ’90s which establishes that bigger human brains are, indeed, smarter (McDaniel, 2005; Rushton and Ankney, 2009). Moreover, they cite Beals et al’s thermoregulatory explanation for human variation without making mention that this climatic explanation is complementary with a size-intelligence one (e.g Ash and Gordon 2007; see also Schwartzman and Middendor (2009) for hominid evolution in general).

Of course, Cartmill and Smith might be correct in their key assertion. Perhaps different populations are wired differently such that between differences in size don’t entail differences in intelligence. [The consistently positive size/IQ correlation within clinal populations (e.g. Sudanese, Guatemalans, African Americans, Asian Indians, Turks, Chileans, etc) strongly argues against this.] Moreover, it’s rather plausible that the differences are mostly environmental in origin. Finding out, though, requires an honest appraisal of the evidence.

References not cited above.

Ash and Gordon, 2007. Paleoclimatic Variation and Brain Expansion during Human Evolution

Beals, et al., 1984. Brain Size, Cranial Morphology, Climate, and Time Machines

McDaniel, 2005. Big-brained people are smarter: A meta-analysis of the relationship between in vivo brain volume and intelligence

Reader et al., 2011. The evolution of primate general and cultural intelligenc

Rushton and Ankney, 2009. Whole Brain Size and General Mental Ability: A Review

Schwartzman and Middendor, 2009. Was climate the prime releaser for encephalization? An editorial

Smith and Beals, 1990. Cultural correlates with cranial capacity

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12 Responses to …But not the same size

  1. Kiwiguy says:

    Thanks for including links to the papers by Beals. When New Scientist reported on the Schwartzman and Middendorf research a couple of years ago they quoted Dean Falk who said she would like to see some research showing continental differences. Particularly:

    “”In principle, I’m receptive to the hypothesis,” says Dean Falk, a palaeoanthropologist at Florida State University in Tallahassee, “but I need the data.” She says that if measurements showed that people living in tropical countries today have smaller brains relative to their body size than people in temperate climates, this would go against expectation and lend support to Kleidon’s model.”

    I forwarded Falk a copy of Rushton & Ankney’s 2009 paper and she emailed back thanking me. I might forward on the link to the Beals paper.

    • Chuck says:

      My guess is that a lot of the difference is environmental; based on Beals there is a ~1.2 SD average difference between Africans and Europeans; between African-Americans and European Americans the difference is maybe ~.3SD at most and some of the data shows an AA advantage. It’s hard to say. By the way, did you see that Holloway commented on my “Brain size and correlates with IQ” post? http://stuffliberalshate.wordpress.com/2010/12/12/22/#comment-152

      • Kiwiguy says:

        ***By the way, did you see that Holloway commented ***

        Impressive, I wonder what other academics have read this site?

      • Steven says:

        The European African iq gap is like 1.5-2sd with a 1.2sd in head size…so where does that leave us? with more than a 0.3 sds of the white black iq gap explained by head size i assume. do you have a bigger article on this?

  2. Kiwiguy says:

    The Angel comment in the 1984 Beals paper is a good example of the kind of fraudulent discussion you mention. Also, this in the reply from Beals:

    “We have no contribution to make toward understanding how
    the brain functions. It is true that 4,000 generations is theoretically
    sufficient time for selection to “iron out kinks and
    equalize intelligence.” The point is that no matter how many
    generations are involved, no sufficient evidence has ever been
    presented that variation in population brain size, head size,
    head shape, or cranial capacity has a connection to intelligence
    in the first place.”

  3. Kiwiguy says:

    True, although Angel introduces a moral perspective to possible interpretations. Angel was happy to discuss brain-size differences provided they didn’t relate to intelligence.

    “I taught these things in turn with pleasure because they explain
    modern brain-size differences in terms of climatic determination
    of mass-surface relations rather than intelligence. No one
    except N*zis or White suprem@cists could then see biological
    differences in intelligence between any surviving groups.”

  4. Kiwiguy says:

    Oh I’ve just read the New Scientist report, not their full editorial.


  5. Pingback: Gould’s Mismeasurement « Occidentalist

  6. Meng Hu says:

    Great article. This is what Richard Lynn explained in his book : “Race Differences in Intelligence: An Evolutionary Analysis”. Smaller crania are found in warmer climates; the “selection pressure” enhance intelligence in cold environment.
    However, a question remains. (I don’t know whether you have already dealt with the subject)
    This articles (3 pages) points out that :

    Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. […] As the brain shrank, its wiring became more efficient, transforming us into quicker, more agile thinkers. […] As the planet warmed, selection might have favored people of slighter stature. So, the argument goes, skeletons and skulls shrank as the temperature rose—and the brain got smaller in the process. […] The observation led the researchers to a radical conclusion: As complex societies emerged, the brain became smaller because people did not have to be as smart to stay alive. […] Some 30 animals have been domesticated, he notes, and in the process every one of them has lost brain volume—typically a 10 to 15 percent reduction compared with their wild progenitors.

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