Transcript What is evolution?

The Historical Development
of Evolutionary Theory
LIFS 691
Advanced Evolution
What is evolution?
• change in the distribution of phenotypes
• change in genotypic frequencies
• change in allelic frequences
• to unfold, open, or unfold (Webster’s Dictionary)
Mechanisms of Evolution
• Natural Selection
(including sexual selection)
• Genetic Drift
• Mutation
• Gen Flow
Natural Selection
• defined as the differential survival and
reproduction of heritable phenotypic
variants
• without heritability of phenotypes, the
process is merely “selection”
Lamarckism was alive and well
in the late 19th century.
• Darwin’s theory could not
overcome problems created
by the theory of Blending
Inheritance
Jean-Baptiste Lamarck
(1744-1829)
• Only about 1/3 of biologists
at the time subscribed to
Darwin’s theory of Evolution
by Natural Selection; many
evolutionary biologists still
agreed with Lamarck’s ideas.
Mendel’s garden
Gregor Johann Mendel
(1822-1884)
“Discovery” of Mendel’s Work
• Provided a theory of particulate
inheritance, which seemingly
overcame problems imposed by
the theory of blending inheritance.
Mendel’s peas
• Unfortunately, many traits are not
controlled by a single polymorphic
locus; thus, Mendel’s laws did not
have immediate generality. Many
still doubted natural selection was
the primary mechanism of
evolution.
The Birth of Mutation Theory
• Noted sudden origins of seemingly
novel phenotypes after many
generations of stability
• Hypothesized that biochemical changes
were occurring, which became known
as mutations.
(Actually, these changes were the
product of hybridization between species
of plants, but this was unknown at the
time.)
Hugo de Vries
(1848-1935)
primroses
Beginning of NeoDarwinian Theory
Sewell Wright
Sir Ronald Fisher
(or Bakken’s lost twin?)
An Alternative Synthesis
• Some approached evolution theory
from an understanding of genetics
and development.
Richard Goldschmidt
• Goldschmidt’s ideas were made
unpopular to protect selectionist
theories from the threat of
mutationist theories. Today, he is
most remembered for the concept
of a “Hopeful monster,” which was
a only a very small part of his
contribution to evolutionary biology.
“Competing” Views in Evolution
• Neutral Theory vs. Selectionist
Theories
• Adaptationist vs. Anti-adaptationist
• Optimization vs. Quantitative Genetic
Theories
Methods for Examining Genes
• Candidate Loci
• Electrophoresis (mid-1960’s)
• Sequencing (mid-1970’s)
• Genomics (mid-1990’s)
“In ‘nothing in biology makes sense except in the light of
evolution’, nothing in evolution makes sense except in the light
of population genetics.”
Richard Lewontin, Harvard University
“The science of population genetics is the auto mechanics of
evolutionary biology.”
Rama S. Singh, McMaster University
Singh (2003), Genome 46: 938-942
Hardy-Weinberg Equilibrium
Assumptions:
•
•
•
•
•
•
No selection
Infinite population size
Random mating
No mutation
Simple genetic system (one locus, two alleles)
Non-overlapping generations
Hardy (1908), Science
Hardy-Weinberg Equilibrium
p = frequency of allele A
q = (1-p) = frequency of allele a
At equilibrium the frequencies of genotypes
is as follows:
AA
p2
Aa
2p(1-p)
aa
(1-p)2
Hardy (1908), Science