Evolution Biol 4208

Lecture 2, Chapters 1 and 23 (22 older version of the book)


Objectives for today

  1. Evolutionary theory after Darwin
  2. Evidence for evolution


Steps in the process of evolution by natural selection

  1. Common ancestor
  2. Variation arises
  3. Unfavorable variants die or fail to reproduce
  4. Favorable variants reproduce and increase in frequency
  5. Frequency of kinds of individuals is altered

Two major components of Darwin’s evolutionary theory?

  1. Common ancestry
    1. Changes in lineages over time not a totally novel idea
    2. Common descent largely accepted by 1870’s
    3. Link between fossil record and relationships between extant species supported by advances in:

                                                              i.      Paleontology

                                                            ii.      Comparative morphology

                                                          iii.      Comparative embryology

  1. Natural selection
    1. Most people rejected Darwin’s mechanism of evolution

Why was natural selection rejected?

  1. Emphasis on competition and death considered immoral
  2. Left little room for teleology (purpose) and progress
  3. Too slow relative to estimates of earth’s age at that time (10-100 myo)
  4. Didn’t work with blending inheritance
  5. Mendel’s work had not yet been rediscovered

Would it have mattered if Darwin met Mendel? Probably not

  1. Contemporaries Mendel (1822-1884) Darwin (1809-1882)
  2. Mendel read Origin of Species (1859) after doing experiments but before publishing in (1865)
  3. Darwin didn’t read Mendel’s paper but had a book that referenced his work
  4. Mendel never argued that his ratios were universal
  5. Darwin considered the answer to heredity to lie in development

Evolutionary Theory after Darwin

  1. NeoLamarckism
    1. Environment effects development and these changes are inherited
  2. Orthogenesis
    1. Species evolve in a predetermined direction without natural selection (no mechanism) 
  3. Mutationists
    1. Grossly distinct phenotypes arise by mutation and produce new species
    2. Goldschmidt 1940 – sudden drastic changes reorganize the whole genome 
    3. Most deleterious – but produces some “hopeful monsters”

Evolutionary synthesis (1930-1950)

  1. Integrated contributions of genetics, systematics, and genetics
  2. Fisher, Haldane, and Wright developed mathematical theory of population genetics
  3. Mutation and selection work together cause adaptive evolution
    1. Mutation provides the raw material of evolution
    2. Natural selection molds that variation for adaptation

Series of influential books

1937:  Dobzhansky. Genetics and the origin of species

1942:  Mayr. Systematics and the origin of species

1944:  Simpson. Tempo and mode in evolution

1950:  Stebbins. Variation and evolution in plants

1953: Simpson. The major features of evolution

1959:  Rensch. Evolution above the species level


a.      Processes operating within populations

                                                  i.      Mutation

                                                ii.      Recombination

                                              iii.      Selection


b.      Accounts for the origin of new species and the formation of higher taxonomic levels

Molecular genetics has had a broad impact

  1. Molecular evolution – To what extent is evolution at the molecular level driven by random chance versus natural selection?
  2. Evolutionary developmental biology – How do developmental processes evolve and how does development constrain possible changes?
  3. Evolutionary genomics – What are the patterns of evolution for multiple genes and whole genomes?
  4. Ecological genetics – What contemporary evolutionary patterns can be observed in wild populations of organisms?


What are the primary sources of evidence for evolution?

  1. Fossil record
    1. Shows intermediate forms
    2. Are there gaps?

                                                              i.       Yes!

  1. Phylogenetic and comparative studies
    1. Trees made by independent sources of data agree
    2. Traits of related species grade
  2. Genes and genomes have similar characteristics
    1. Universal genetic code
    2. Machinery of nucleic acid replication
    3. Share “selfish” genetic elements that are generally maladaptive
    4. Commonality of structure and function of genes allows advances in human biology via the study of model organisms
  3. Biogeography
    1. Pattern of speciation in Hawaiian matches the pattern of island formation
  4. Contemporary evolution
    1. Timing of life cycle events in response to climate change
    2. é spring temps
    3. é food supply
    4. Breed 6 days earlier per generation in last 10 yrs
    5. 3.7 days plastic response
    6. 2.3 days genetic change