Bio. 230 --- Evolution III
Some History of Evolutionary Thought
Empedocles (Greek, ~490 to 430 B.C.)
1st to propose a clear concept of biological
evolution
Abiogenesis
Plants arose 1st; their buds gave rise to animals
Gradual process
Some History of Evolutionary Thought
Aristotle (Greek, 384-348 B.C.), student of
Plato (~427-347 B.C.)
Similar ideas
Abiogenesis
Acquired characteristics
Species could hybridize
Some History of Evolutionary Thought
Lamarck (French, 1744-1829)
1st in more modern times to put forth a
comprehensive & logical evolutionary theory
Acquired characteristics
Pangenesis / pangenes
Newer forms were more complex (and
“perfect”) than their ancestors
Some History of Evolutionary Thought
Charles Darwin (English, 1809-1882)
Started out as a special creationist
READ handout: “A comparison of views on
variation and heredity”
1831-1836 --- voyage on the Beagle
Then worked for more than 20 years
1838 – He read AN ESSAY ON THE PRINCIPLE OF
POPULATION by Thomas Malthus
Natural Selection
Some History of Evolutionary Thought
Charles Darwin (English, 1809-1882)
1844 -- Put together a brief essay (unpublished)
Early 1858 – Essay from Alfred Russel Wallace
Later 1858 – Published Wallace’s essay and
excerpts from his own 1844 essay in the
Journal of the Linnaean Society
1859 – published THE ORIGIN OF SPECIES BY
MEANS OF NATURAL SELECTION
Darwin’s Main Points
1) Overproduction of offspring
2) Variation within a species and at least some
of it is hereditary
3) Limits on resources; engenders a struggle
for existence
4) Generally the fittest survive
(= Natural Selection)
5) Eliminating of unfavorable traits and
accumulation of more favorable traits
gives rise to new forms of life
NeoDarwinism or The Modern Synthetic Theory
Darwin did not have all the answers
1937 – Theodosius Dobzhansky (Genetics and
the Origin of Species) began the MST
1950s to 1970s additional seminal work
C. Leo Babcock (plant evolution),
Edgar Anderson (Introgressive Hybridization),
Earnst Mayr (animal evolution),
G. L. Stebbins (plant evolution),
J. Watson & F. Crick (DNA structure),
M. Nirenberg & J. H. Matthaei (genetic code)
Evolutionary Potpourri
Evolution occurs in POPULATIONS*
Populations can have a change in gene / allele frequency
All populations are phenotypically polymorphic
New gene / allele combinations can come about from
CROSSINGOVER and RECOMBINATION during sexual
reproduction
New alleles / genes come about by some type of MUTATION
Microevolution* vs. Macroevolution*
Are the processes that drive each different?
Gradualism vs. Punctuated Equilibrium*
Are the processes that drive each different?
The Gene Pool (I)
DEFINITION* -- ALL of the genes AND alleles in a
population taking into account their frequency
It is the total supply of genetic units available to
form the next generation
Not possible to study the whole gene pool
Will look at a “mini” gene pool (for the gene “A”)
Only two alleles: A and a
3 possible genotypes (AA, Aa, aa)
We start a population with a certain frequency
of A and a
The Gene Pool (II)
What will happen to the allele (and genotype)
frequencies over the generations??????????
Solved independently in early 20th century by:
George Hardy & Wilhelm Weinberg
Known by various aliases:
Hardy-Weinberg Equilibrium
Hardy-Weinberg Theorem
Hardy-Weinberg Law
Hardy-Weinberg Equilibrium
DEFINITION* -- Given certain conditions the
allele frequencies remain constant from
generation to generation AND after one
generation of random mating even the
genotype frequencies will remain constant
and can be predicted from the equation
(p + q)2 = p2 + 2pq + q2
p = the frequency (f) of A
q = the frequency (f) of a
p2 = f AA, 2pq = f Aa, q2 = f aa
Hardy-Weinberg Conditions (I)
Infinitely large Population
Eliminates chance fluctuations (genetic drift)
Random Mating
Means no inbreeding; no positive (+) or
negative (-) assortative mating
No net mutation
Eliminates mutation pressure
No net population movement
Eliminates net gene flow
Hardy-Weinberg Conditions (II)
No natural selection
Means no type is better than another; all
types must survive at proportional rates
----------------------------------------------------------------“Survival of the Fittest” does not mean that
organisms fight or that organism have to die
Death (real) vs. Genetic Death
Natural Selection works on PHENOTYPE
Genetic Drift
A change in the allele frequencies in
a gene pool due to random (chance) events
More likely to happen in small populations
OR when a small sample is taken from a large
population
Due to random sampling in a less than infinite
population
Genetic Drift
Genetic Drift / Bottlenecking / Founder Effect
Some Species Concepts
Many concepts; none are ‘perfect’
Morphospecies (= typological sp.)
Biological species (= reproductive sp.)
(E. Mayr)
Phenetic species
Ecospecies
Phylogenetic species
Phyletic Speciation (Anagenesis)
Number of extant
species does not
increase
Divergent Speciation (Dichotomous speciation
or Cladogenesis)
Number of extant species increases
Isolating Mechanisms
See handout
Autopolyploidy (Fig. 24.10) ???????????
Allopolyploidy (Fig. 24.11) ???????????
Allopolyploidy (MOST likely)
(2 pathways --- many examples)
(Primula kewensis and Tragopogon mirus)