Misuse of Selection/Heritability
Chapter 6, Page 208-210
• Theory of population genetics allows us predict course of evolution.
• As long as we know starting allele frequencies and genotype fitnesses, model can predict how allele
frequencies change, under variety of selection schemes.
• Model can make fairly accurate predictions in natural populations.
• Phenotype that caught eugenicists attention was feeblemindedness.
• Feeblemindedness defined as “One who is capable of earning living under favourable circumstances, but
is incapable from mental defect existing from birth or from early age (a) of competing with an equal
terms with his normal fellows or (b) of managing himself and his affairs w/ ordinary prudence”
• Henry H. Goddard convinced eugenicists that strength of mind behaved like simple Mendelian trait.
Normalmindedness believed be dominant and feeblemindedness was recessive.
• Rare recessive alleles decline in frequency slowly even under strong selection.
• Eugenicists did not believe that feeblemindedness especially rare.
• Over 10 generations, about 250 years, frequency of affected individuals declines from 0.01 to 0.0025.
• Some looked at numbers, saw that would take very long time to completely eliminate feeblemindedness
and argued compulsory sterilization was such hopeless slow solution that it was not worth the effort.
• Fisher noted that most copies of allele for feeblemindedness present in heterozygous carriers rather than
• Goddards evidence was deeply flawed. First, individuals whose case studies he reported a highly diverse
group. Second, Goddard’s methods for collecting data were prone to distortion. Caseworkers relied on
hearsay and subjective judgements to assess strength of mind of family members. Third, Goddards
methods of analysis stacked cards in favour of his conclusion. Given how he had filtered data ahead of
time, not too surprising he concluded feeblemindedness as Mendelian.
• Although feeblemindedness is not among them, many genetic diseases now known to be inherited as
simple Mendelian traits.
Chapter 9 (Page 350 – 355)
9.7 – The Bell-Curve Fallacy and Other Misinterpretations of Heritability
• Formula of heritability includes both genetic variation,GV and environmental variation, E .
• 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 e