Evidence for Darwinian Evolutionary Theory

1
Evidence for Darwinian Evolutionary Theory

• Multiplication of sp.
• evolution is branching process, thus sp. ? w/
  time
• some go extinct
• sp. descend from common ancestor, ability to
  interbreed, genetic and phenotypic cohesiveness
• sibling sp. indistinguishable phenotypically
  but different mating rituals
• reproductive barriers factors that prevent
  interbreeding
• prezygotic (premating) vs. postzygotic
  (postmating)
• examples of each

2
Evidence for Darwinian Evolutionary Theory

• speciation is result of genetic isolation and
  divergence
• 2 categories of speciation
• allopatric speciation (a.k.a. geographic
  speciation) sp. arise when physically separated
• vicariant speciation, dispersal/colonization
  (a.k.a. founder event)
• sympatric speciation (a.k.a. geographic
  speciation) sp. arise when living in same
  geographic area
• polyploidy in higher plants, niche
  differentiation
• adaptive radiation diversification that results
  in many ecologically different sp. from common
  ancestor
• due to founder events, single fertilized ?
• often seen in isolated geographic areas

3
Evidence for Darwinian Evolutionary Theory

• Gradualism
• small continuous changes accumulate over time and
  result in major differences among sp.
• controversial b/c opposes sudden origin of sp.
• similar to Lyells uniformitarianism
• population gradualism new traits est. in
  population by increasing their frequency in a
  population
• phenotypic gradualism new traits produced in
  small, incremental steps
• phyletic gradualism morphological changes are
  small/continuous, occurs w/i unbranched lineages
  over time

4
Evidence for Darwinian Evolutionary Theory

• Niles Eldredge and Stephen Jay Gould propose
  concept of punctuated equilibrium to explain
  discontinuous evolutionary changes
• punctuated equilibrium phenotypic evolution
  concentrated in brief events resulting in
  phylogenetic branching followed by long, static
  periods
• contrast to phyletic gradualism
• speciation is brief episode in sp. history (1 of
  sp. time)
• due to allopatric speciation by founder event b/c
  small founding population

5
Evidence for Darwinian Evolutionary Theory

• Natural selection
• 1 mechanism by which evolution occurs
• means of adaptations that enhance
  survival/reproduction
• 5 observations 3 inferences
• ob. 1 organisms have great potential fertility
• ob. 2 populations remain fairly constant, no
  prolonged exponential growth
• ob. 3 limited natural resources, thus
  exponential growth cannot occur for prolonged
  periods
• inf. 1 struggle for existence, esp. as
  overpopulation occurs
• ob. 4 variation w/i populations
• ob. 5 some variation is heritable
• inf. 2 differential survival and reproduction
• inf. 3 differential survival and reproduction
  leads to adaptations and new sp.

6
Revisions to Darwins original theory

• Neo-Darwinism
• prior Mendel and Chromosomal Theory of
  Inheritance, Darwin accepted blending hypothesis
  and Lamarckism
• neo-Darwinism Lamarckism disproved and
  understanding of inheritance
• evolutionary biology divided into 2 subfields -
  microevolution and macroevolution
• microevolution change in gene pool of
  population
• macroevolution large scale evolutionary change
• includes origin of novel design, evolutionary
  trends, adaptive radiation, mass extinction

7
Microevolution

• Microevolution addresses changes in gene pool w/i
  population
• gene pool all alleles of all genes possessed by
  all members of population
• polymorphism different allelic forms of a gene
• lots of polymorphisms w/i population
• researchers study allelic frequency
• allelic frequency relative frequency of
  particular allelic form w/i population

8
Microevolution

• Hardy-Weinberg equilibrium
• foundation of population of genetics
• allelic frequencies and genotypic ratios at
  equilibrium remain constant (no evolution is
  occuring)
• (p q)2 p2 2pq q2
• review albinism problem p. 121 and box p. 122
• mutations, NS, migration, nonrandom mating,
  genetic drift disrupt equilibrium and sources of
  microevolutionary change

9
Microevolution

• genetic drift random change in allele frequency
  in population
• problem in populations w/ little genetic
  variation
• can lead to loss of alleles or fixation
• nonrandom mating selecting mates for some
  characteristic
• positive assortative mating mating of like
  individuals genotypically
• ? homozygosity, ? heterozygosity, doesnt ?
  allele frequency
• inbreeding mating of close relatives
• migration mvmt of alleles btwn populations
• prevents genetic divergence
• NS
• sexual selection selection of traits useful for
  obtaining mates
• mutation change of a gene, heritable
  modification of a trait

10
Microevolution

• Responses to selection
• stabilizing selection favors average, disfavors
  extremes
• directional selection favors one extreme and
  not the other
• disruptive selection disfavors average, favors
  extremes

11
Macroevolution

• Macroevolution describes large-scale events in
  evolution
• speciation btwn micro/macro
• macroevolutionary change results from
  microevolution
• new adaptations and sp. arise
• mass extinctions occur
• marine environment every 26M yrs (asteroid
  bombardment, climate change)
• 2 fates of sp.
• give rise to new sp.
• sp. selection differential survival and
  multiplication of sp. over time w/i lineages
• become extinct (catastrophic sp. selection
  discrimination of sp. by mass extinction events)
• mass extinction large taxa disappear
  simultaneously
• Permian extinction 225 MYA, 90 loss of marine
  inverts.
• Cretaceous extinction 65 MYA, loss of dinosaurs
  others