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HRS 331. HONORS PROGRAM SEMINAR IN SOCIAL SCIENCE:
GENES AND BEHAVIOR
2/4/04:
Behavior Genetics (T. Burk, Biology Department)
Behavior Genetics from the Point of View of an Ethologist
(Ethology = Evolution-Based Study of Animal Behavior)
Classical dichotomies:
Genes vs. Environment
“Nature vs. Nurture”
Instinct vs. Learning
Our modern perspective is that the first two are invalid behavior results from both genes and environment.
all
Examples, cricket songs and human language
Also, while some behaviors are instinctive, and some are learned,
most (at least in animals) combine elements of each. Example, bird
song development
Behavior Genetics: Study of how differences in genes contribute to
differences in behavior (NOT “how genes determine behavior”)
Some Major Methods of Study, with Examples:
1.)
Study existing genetically-different entities, to see if they differ
in behavior
Single gene mutants: “Yellow” Drosophila (M. Bastock)
Inbred strains: Maze learning in rats (Cooper & Zubeck)
(C & Z’s results show that, even where we know there are gene
differences that CAN produce behavior differences, whether or not
they do depends on the environmental circumstances.)
2.)
Mendelian crosses (Do matings between entities that differ in
behavior, to see if the differences are due to gene differences, and
hopefully to determine the nature of the inheritance involved)
Example, Rothenbuhler’s study of “Hygienic” honey bees
3.)
Artificial selection: if this is successful, then differences
between individuals in the original diverse population must have
been at least partially the result of gene differences.
Example, Cade’s study of calling duration in crickets
4.)
Study correlations in behavior among relatives
(in humans, twin studies and adoption studies)
Examples, Hedrick’s study of calling duration in crickets;
Bouchard & McGue’s table of IQ score similarities
A Useful, But Much-Abused Concept in Behavior Genetics HERITABILITY
Definition: The proportion of the variation in a trait among the
individuals within a population that is due to variation between
individuals in their genes.
Formulas:
H = Response to selection/Selection Differential
(H = R/S) (from artificial selection experiments)
H = VG / (VG + VE) (This basically restates the verbal definition,
but is very useful for showing that H is unique for every
combination of population/environment)
Finally, as explained in several of your readings, you can
calculate H using the correlation coefficient from correlational
studies
An egregious example of the misuse of heritability:
“The Race/IQ Controversy”
Jensen and associates misuse heritability in at least three ways:
(1)
They believe that H tells you the role of genes in producing a
trait, not that H merely accounts for differences between individuals
with respect to that trait!
(2)
They believe that H has a constant value for a trait, across
different populations.
(3)
They believe that if H is usually high for a trait, and if
populations differ in that trait, then the differences between the
populations are due to gene differences. (Lewontin’s excellent
examples show the fallacy of this.)