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increased.   Hogben has drawn attention to the importance of this

In various biometric studies, it has been shown that unfavourable
conditions tend to increase the degree of observed variation. But the
attempt to erect this into a general principle cannot be correct, since
the opposite may in other cases hold good. This is so, for instance, in
our fruit-fly example — moist conditions, being associated with abund-
ance and availability of food, are favourable; yet they here increase
variability. A human example of the same sort, also cited by Hog-
ben,2 concerns education. "The effect of extending to all classes of
society the educational opportunities available to a small section of it
would presumably be that of increasing variability with respect to
educational attainment. The effect of depriving the more favoured
of their special advantage would be to diminish variability in educa-
tional attainments." Either policy would result in an equalization
of environment; but equalizing it by making it more favourable
would bring out genetic differences more fully, while the reverse
process would mask them.

However, whether equalizing the environment will in this or that
case increase or decrease variability, what differences then remain
must be genetic in their origin. Thus without either equalizing or
discounting the effect of environment, we cannot be sure what differ-
ences between groups are due to inheritance.

This point is of extreme importance in eugenics. For instance, it
is well known that members of different social classes differ in their
average of stature, physique and intelligence — all of them characters
of the greatest evolutionary importance. I take one or two examples
from Carr-Saunders.3 In a sample of fourteen-year-old Liverpool
schoolboys, the boys from a secondary school were on the average no
less than 6| inches (over 10 per cent.) taller than those from a council
school in a poor neighbourhood; and differences in weight were
equally marked. In a similar investigation in London, the "mental
age" (as determined by intelligence tests) of boys from a superior
school was far above that of boys from a school in a poor neighbour-
hood. Twelve-year-olds from the superior school had a mental age
nearly a year above their real age, while those from the poor school
were a whole year behind their real age—a difference of 15 per cent,

Such differences are usually cited by eugenists as proof of a real and
considerable difference in genetic qualities. For instance, Professor
Carr-Saunders, after quoting these facts, concluded that "so fur as

933? P- "5-                               a Op.
3 Garr-Saundcrs, 1956, pp. 97, 105, xa6,