Howard is certain that people are becoming more intelligent, but is less sure that there's a strong causal association between increasing brain size and IQ. I also respond to the rationale he proposes to explain the upsurge in myopia.
2. Yet, Howard is reluctant to embrace the idea of a causally linked brain-size/IQ relationship, as indicated by his words: "While some brain imaging studies lend some support to [this] notion, much more research is needed" -- versus my evaluation that every relevant MRI study is consistent with the proposition that a moderate positive association exists between IQ and brain size/neocortex size (i.e., correlations clustered around .40-.45). Thus, by consistency of replication, this specialized data base is strengthened.
3. I believe that Howard's view of what constitutes the relevant database is much too restrictive, as it should include studies depicting: (1) the long-term increase in brain weight (e.g., Miller & Corsellis 1977); (2) normative data that children have much larger brains than their grandparents did; and (3) the strong suggestion from MRI studies that young adults have much more gray matter in their association neocortex than people in their mid-forties, and that this change is not due to a loss of gray matter between these ages. In terms of standard deviation, the increases in brain size and IQ have been at similar rates (Lynn 1990), but although this does not ensure that these events are causally related, all available evidence suggests that they are, including studies of rats reared in enriched environments and autopsies of specific cortical areas in people possessing extraordinary gifts of intellect.
4. To explain these phenomena, Howard emphasizes the association between height and IQ, even though this association is roughly 10 times weaker than the brain-size/IQ correspondence. Height is responsive to early nutrition, but for nutrition to be the chief impetus for rising intelligence, one must explain: (1) why, in a given person, nutrition's effects on brain size are so weakly correlated with its effects on height; (2) the rather weak association between IQ and early nutrition found in the studies cited in the target article; and (3) the existence of ethnic groups having both relatively high IQs and a relatively short stature (e.g., the Japanese and Jewish peoples).
5. Howard suggests that the intergenerational increase in myopia may be accounted for by the changes in children's lifestyle (more time spent in front of video screens and in reading), but several lines of evidence argue against this being the dominant causal agent. First, the predisposition to develop myopia is usually apparent in the initial postnatal months (Pacella et al. 1999), before substantial passive reading begins. Second, if myopia was highly sensitive to the amount of such visual stimulation, one would expect that near work would be a stronger determinant of myopia than whether one has one or two myopic parents, rather than the reverse; also, one would expect to have seen a substantial decline in the proportion of myopes with one or two myopic parents in societies where rates have soared, rather than stability. Third, Mutti and Zadnik's (2000) recent analysis does not support the idea that increasing environmental exposures to near work in recent decades has materially changed the prevalence of myopia. Lastly, two new studies (Gwiazda et al. 2000; Zadnick et al. 2000) do not support the theory that use of a night light in infancy fosters myopia's development. Rather, the idea that parental/grandparental near work contributed more to the rise in offspring myopia than did offspring near work, fits these data far better.
Gwiazda, J., Ong, R., Held, R. & Thorn, F. (2000) Myopia and ambient night-time lighting [comment]. Nature 404: 144.
Howard, R. W. (2000)Interrelating broad population trends. PSYCOLOQUY 11(103) ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/2000.volume.11/ psyc.00.11.103.brain-intelligence.3.howard http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?11.103
Lynn, R. (1990) The role of nutrition in secular increases in intelligence. Personality and Individual Differences 11: 273-285.
Miller, A. K. H. & Corsellis, J. A. N. (1977) Evidence for a secular increase in human brain weight during the past century. Annals of Human Biology 4: 253-257.
Mutti, D. O. & Zadnik, K. (2000) Age-related decreases in the prevalence of myopia: longitudinal change or cohort effect? Investigative Ophthalmology & Visual Science 41: 2103-2107.
Pacella, R., McLellan, J., Grice, K., Del Bono, E.A., Wiggs, J. L. & Gwiazda, J. E. (1999) Role of genetic factors in the etiology of juvenile-onset myopia based on a longitudinal study of refractive error. Optometry and Vision Science 76: 381-386.
Storfer, M. (2000) Precis of "Brain size, intelligence and myopia" PSYCOLOQUY 11(083) ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/2000.volume.11/ psyc.00.11.083.brain-intelligence.1.storfer http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?11.083
Zadnick, K., Jones, L. A., Irvin, B.C., Kleinstein, R. N., Manny, R. E., Shin, J. A. & Mutti, D. O. (2000) Myopia and ambient lighting at night: CLEERE study group [comment]. Nature 404: 143-144.