BIOL 4100 Lecture Notes - Jens Clausen, Wildflower, Heritability
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The Bell-Curve Fallacy and Other Misinterpretations of Heritability
•Formula of heritability includes both genetic variation, VG and environmental variation, VE.
•Any estimate is specific to particular population living in particular environment.
•Heritability tells us nothing about causes of differences between populations that live in diff.
•Jens Clausen, David Keck, and William Hiesey studied Achillea, a perennial wildflower. Achillea grew
from cuttings, making it possible to created clones of single individual. Researchers collected seven
plants from wild population and took two cuttings from each.
•Researcher grew one cutting from each plant in experimental garden in Mather, California. As the
cuttings grew up side by side, they experienced virtually the same environmental, differences among
them in height at maturation almost entirely due to genetic variation.
•Researchers grew second cutting from each plant in experimental garden at Standford, California. The
plants experienced virtually same environment, differences among them in height at maturation are
entirely due to genetic variation.
•Plants in Standford population on average taller than plants in Mather population. The fact that
heritability is high in each population tells us nothing about cause of differences between populations,
because populations reared in diff. environments.
•Mistaken notion that heritability tells us something about causes of diff. between populations has been
persistent in studies of human intelligence.
•Murray and Herrnstein claimed that difference in average IQ scores between African Americans and
European Americans is due to genetic differences between these groups. They understood that I.Q. is
substantially heritable yet does not tell us anything about origin of difference between groups.
•Murray and Herrnstein proceeded to develop erroneous arguments.
•They imagined that 60% of the variation w/in each group was due to genetic variation leaving 40% of
original variation w/in each group.
•At least two serious flaws in Murray and Herrnstein’s argument. First, they assume there is linear
relationship between environment and IQ.
•Second, Murray and Herrnstein’s argument from own incredulity amounts to rhetorical technique, not
science. Scientific approach to their hypothesis would be to conduct common garden experiment: Rear
European Americans and African Americans together in environment typically experienced by European
Americans, then compare IQ scores and vice versa. Experiment cannot be done with humans. It might
be suggested that could study adopted African American and European American children into similar
families. But even though they might have lived in similar families, might experience diff.
environments. Since cannot do this experiment, have no way to access whether genetics has anything to
do w/ difference in IQ score between ethnic groups.
•Jens Clausen, David Keck, and William Hiesey conducted series of common garden experiments w/
Archillea. Plants in this genus collected from low-altitude populations make more stems than plants
collected from high-altitude populations. When plants from low altitude and plants from high altitude
grown together at low altitude, low-altitude makes more stems, therefore, consistent w/ hypothesis plants
from low altitude are genetically programmed make more stems. When low-altitude and high-altitude
plants grown at high altitudes the high-altitude plants make more stems. Reveals genetic diff. between
low- and high-altitude plants in way each responds to environment. Also reveals that each population of
plants is superior in its own environment of origin.
•Only way to determine cause of difference between populations is to rear individuals from each of
populations in identical environments.
•Heritability of a trait allows us to predict whether selection on the trait cause a population to evolve.