Bio. 230 --- Evolution III

Some History of Evolutionary Thought

Empedocles (Greek, ~490 to 430 B.C.)

1st to propose a clear concept of biological evolutionAbiogenesisPlants arose 1st; their buds gave rise to animalsGradual process

Some History of Evolutionary Thought

Aristotle (Greek, 384-348 B.C.), student of Plato (~427-347 B.C.)

Similar ideasAbiogenesisAcquired characteristicsSpecies could hybridize

Some History of Evolutionary Thought

Lamarck (French, 1744-1829)

1st in more modern times to put forth a comprehensive & logical evolutionary theoryAcquired characteristicsPangenesis / pangenesNewer forms were more complex (and “perfect”) than their ancestors

Some History of Evolutionary Thought Charles Darwin (English, 1809-1882)

Started out as a special creationistREAD handout: “A comparison of views on variation and heredity”1831-1836 --- voyage on the BeagleThen worked for more than 20 years1838 – He read AN ESSAY ON THE PRINCIPLE OF POPULATION by Thomas MalthusNatural Selection

Some History of Evolutionary Thought

Charles Darwin (English, 1809-1882)

1844 -- Put together a brief essay (unpublished)Early 1858 – Essay from Alfred Russel WallaceLater 1858 – Published Wallace’s essay and excerpts from his own 1844 essay in the Journal of the Linnaean Society1859 – published THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION

Darwin’s Main Points

1) Overproduction of offspring2) Variation within a species and at least some

of it is hereditary3) Limits on resources; engenders a struggle

for existence4) Generally the fittest survive

(= Natural Selection)5) 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 answers1937 – Theodosius Dobzhansky (Genetics and the Origin of Species) began the MST1950s 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 frequencyIt is the total supply of genetic units available to form the next generationNot possible to study the whole gene poolWill look at a “mini” gene pool (for the gene “A”)Only two alleles: A and a3 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 WeinbergKnown by various aliases: Hardy-Weinberg Equilibrium Hardy-Weinberg Theorem Hardy-Weinberg Law

Hardy-Weinberg EquilibriumDEFINITION* -- 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

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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

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 speciesEcospeciesPhylogenetic 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)