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Bio. 230 --- Evolution III - PowerPoint PPT Presentation
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Bio. 230 --- Evolution III. Some History of Evolutionary Thought . Empedocles (Greek, ~490 to 430 B.C.) 1 st to propose a clear concept of biological evolution Abiogenesis Plants arose 1 st ; their buds gave rise to animals Gradual process. Some History of Evolutionary Thought .
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Bio. 230 --- Evolution III
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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1844 -- Put together a brief essay (unpublished)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
Overproduction of offspring
Variation within a species and at least some of it is hereditary
Limits on resources; engenders a strugglefor existence
Generally the fittest survive(= Natural Selection)
Eliminating of unfavorable traits and accumulation of more favorable traitsgives 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 workC. Leo Babcock (plant evolution),Edgar Anderson (Introgressive Hybridization),EarnstMayr (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 ap2 = f AA, 2pq = f Aa, q2 = faa
Hardy-Weinberg Conditions (I)
Infinitely large PopulationEliminates chance fluctuations (genetic drift)
Random MatingMeans no inbreeding; no positive (+) or negative (-) assortative mating
No net mutationEliminates mutation pressure
No net population movementEliminates net gene flow
Hardy-Weinberg Conditions (II)
No natural selectionMeans no type is better than another; all types must survive at proportional rates
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“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
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
Allopolyploidy (MOST likely)(2 pathways --- many examples)(Primulakewensisand Tragopogonmirus)
