individual. It is within this framework that the other two effects
It is interesting to note that there is some evidence that the
genetic effect is less important in certain age groups, specifically
the preschool age group. Habicht et al. (1974), Johnston et al. (1976),
Martorell et al. (1975) and Neumann (1979) argue that the genetic
effect on the growth of preschool children is relatively small, espe-
cially when compared to environmental influences (i.e. nutrition and
disease). Furthermore, genetics becomes expressed more strongly after
the onset of adolescence (Johnston et al. 1976). With respect to
ethnic differences exhibited in preschool growth, Martorell et al.
(1975: 527) states:
The data in the literature indicate that the marked dif-
ferences that exist in growth between populations of the
Third World and those of developed countries, are due
principally to environmental factors--poor nutrition and
illness--and not to genetic factors.
Johnston et al. (1976) examined and compared two ethnic groups: United
States born (living in the U.S.), United States born (living in Guate-
mala) and Guatemalan born (living in Guatemala); all from the same
socioeconomic level. They found that, in preadolescent children,
there were no ethnic and/or genetic differences in growth. By com-
paring the two American groups under different environmental conditions,
there were discrepancies noted in growth; even though they exhibited
the same blood group frequencies, which denote the same ethnic group.
Also, the Americans living in Guatemala were very similar in growth
to the native Guatemalans, though, based on their blood group fre-
quencies, they were markedly different ethnically. On the basis of
Rodeheaver, Daniel Gilbert, 1954-; Bates, Frederick L. & Murphy, Arthur D. Malnutrition And Food Aid Programs: A Case Study From Guatemala. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc84342/. Accessed March 1, 2015.