Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

Physical Environment and Mental Development 331
with poverty and with poor mental development, such as prematurity,
low birth weight, poor health care, high incidence of
infectious diseases, child neglect, and so on. Also, as Platt (1968,
p. 241) points out:
The effects of maternal undernutrition and those of genetic
factors are difficult to separate in disadvantaged populations.
Since consequences may be similar and are exhibited even in
fetal death, there is often no way to separate these factors in
the individual case. Human population and biostatistical studies
must be conducted in order for scientists to understand the
subtle interactions of genetic endowment and nutrition within,
and between, the larger genetic pools of any given geographical
or socioeconomic group.
Two or three studies of human malnutrition, however, have
involved more or less adequate controls and have yielded sufficiently
clear-cut results to warrant the conclusions of one of the
leading researchers in this field: ‘There can be absolutely no
question about the association of significant degrees of malnutrition
during the early years of life and concurrent as well as later
manifestations of intellectual impairment’ (Birch, 1968, p. 57).
I have found a total of only thirteen published studies of the
effects of nutrition on mental development. Eleven of these are
well summarized by Stein and Kassab (1970), who do not include
a study conducted in Peru (Pollitt & Granoff, 1967) or the one
published United States study (Harrell, Woodyard & Gates, 1955).
It is significant that all but one of the studies showing any mental
effects of nutritional deficiency were conducted outside the United
States in those parts of Africa, Asia, and Central and South
America which suffer the most extreme poverty and proteincalorie
deficiency.1 It is interesting that even in these localities
the degree of malnutrition sufficient to depress mental development
is not found generally in any appreciable segment of any
population; these malnourished cases must be sought out in
specific families, and even then usually not all the children in the
same family will show signs of malnutrition. The impression that
many persons seem to have gained from the popular press, that
there are hordes of malnourished children who suffer mental
retardation therefrom, is quite at odds with the actual picture given
by the total body of scientific literature on this subject. Children