BIOL 4160 Evolution Phil Ganter 301 Harned Hall 963-5782
Acharia (Sibine) stimulea, the saddleback caterpillar, armed with urticating spines and advertising it!

The Origins of Evolutionary Questions and Theories

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Link to a list of Specific Objectives for lectures

Back to:

• Evolutionary and Biology
• Evolution Before Darwin
• Important Contributions
• Darwin's Contribution
• Evolution Just After Darwin
• Evolution Today

General comments

Evolution and Biology

Evolution is affected by and effects all areas of biology - even clinical biology

• Evolution is at the center of several fields - ecology, bioinformatics, demography, epidemiology to name a few
• Evolution has found uses in other fields in that it represents a method of searching for optimal solutions
• Some computationally intractable design problems are amenable to solution through what is known as "evolutionary computation"

Evolutionary ideas current in biology

• Separation of Phenotype and Genotype
• No inheritance of acquired characteristics
• Mutation is random and is the source of genetic variation required by evolution
• Gradual change is the most common form of change and can produce great phenotypic differences over geologic time
• Natural Selection, Genetic Drift, (and Sexual Selection) are the most effective forces in evolution
• Many phenotypic characters are affected by numerous genes at different loci

Evolution before Darwin - A selection of those who speculated on the nature of living things prior to Darwin's book

• Some Greeks
  • ~520 BC - Anaximander
    • speculation on variability in a species and proposed that species changed over time
    • speculated that life had a single origin and that it was simpler in the past and has become more complex
• ~500 BC - Xenophanes
  • Thought fossils held the key to earlier form of life and speculated about evolution of living forms
• ~350 BC - Plato and Aristotle
  • Plato and Essentialism
  • Aristotle and Species as types
  • Aristotle and ties to Christian thought
• 1686 - John Ray proposes similar species are similar due to descent from common ancestor in his book on plants
• 1735 - Karl Linne (Carolus Linnaeus) proposed a hierarchical scheme that he felt revealed a divine order of living things in his book on classification
• 1749 - Comte de Buffon proposed a modern definition of species based not on morphological similarity but on the ability to produce fertile offspring although he felt that species were fixed on a divine scale that, surprisingly, placed man at the summit
• 1770 - Charles Bonnet proposed that organisms responded to natural catastrophes by evolving (a bit "natural selection"-ish) and that this evolution followed a pre-determined path (not "natural selection"-ish)
  • To Bonnet, apes were becoming men and men were becoming angels as they evolved.
• ~1780 - Immanuel Kant proposed a common origin for living things and diversification based on need in different circumstances
• ~1800 - Georges Cuvier, a founder of animal paleontology, was convinced that species go extinct but felt that no new species could arise and that evolution was impossible
  • Catastrophism - proposed the idea that catastrophes had caused mass extinctions to explain why fossils of different strata differed and why the boundaries between strata were sharp and not gradual
• ~1800 - Erasmus Darwin (our guy's granddad) agreed with Anaximander that all living things were descended from a single ancestor and that they had diversified into the various forms seen today due to competition and social interaction
• 1809 - Chevalier de Lamarck proposes separate origins for species through spontaneous generation and subsequent change by the inheritance of acquired characteristics.  Characteristics changed as our use of them changed and these changes were passed on to the next generation
  • More complex forms has formed earlier and had more time to become complex.
  • each species evolves toward a goal

Important Contributions from Geology and Social Science

• James Hutton proposed that most geological change was small (volcanoes and earthquakes were exceptions) and that the Earth was old, allowing for great change to have accumulated (Gradualism)
• Charles Lyell combined Gradualism with a second idea, that the forces of geological change seen today are the same as have been operating since the origin of the Earth, so we may understand ancient changes by studying current change (Uniformitarianism)
• Thomas Malthus observed that resources were either fixed in amount or increased in a linear fashion and that organisms that used those resources increased not linearly but geometrically
  • Felt that all organisms were fated to experience resource shortage when their capacity for increase caught up to the amount of resource available
  • The inevitable outcome was competition (accompanied by vice and misery unless tempered by virtue).

Darwin's Contribution

• Started with the observation that life has changed over time (evolution as a fact)
• His encyclopedic data were important in establishing this as a fact, although many biologists and geologists had documented evolution by Darwin's time
• Accepted descent from common ancestor
• Accepted Gradualism and Uniformitarianism
• Focused on change within populations and documented variation among individuals within a population
• A population is a local group of interbreeding organisms
• Big Contribution - proposed Natural Selection as the mechanism by which evolution proceeds

Evolution Soon After Darwin

Darwin's mechanism was not immediately accepted, although his documentation of variation and change convinced biologists of the fact of evolution

Many years of speculative theorizing about mechanism of evolution

• Neo-Lamarckianism - acquired characteristics regained popularity but A. Weismann demonstrated that cutting the tails off of mice never became an inherited characteristic
• Orthogenesis - disagreed that the environment set the course of evolution, especially over long periods and at higher taxonomic levels
  • they felt that organisms progressed toward a set goal over time (this sort of idea is very old - remember Lamarck's idea that all species begin as simple organims and progress in complexity toward their ultimate destiny)
• Mutationism - mutationists felt that evolution occurred in discrete jumps (remember, mutation had very different conotations before the rise of genetic and the discovery of DNA as the heredity molecule)
  • New species originated when they mutated from pre-existing species, but this process was independent of natural selection, which only affected the composition of populations (below the species level)

• Twentieth Century Evolution
  • Mendel represented a challenge to Darwin's gradualism
    • Mendelists (Saltationists, Mutationists - Galton) claim that Medel showed that genetic change was discrete and sudden, not continuous and gradual (data from discrete characters)
    • Biometricians (Pearson, Weldon), who used different models of evolution, claimed that genetic change was gradual and continuous (data from multifactorial characters)
  • Modern (Evolutionary) Synthesis of Mendelism and Evolutionary Theory (R. A. Fisher, J. B. S. Haldane, Sewall Wright)
    • Response to controversy, developed models of evolution of discrete mutations that resulted in evolutionary change consistent with Darwin's predictions of gradual change and that discrete mutations could lead to continuous change if multiple loci affected the character
    • Population Genetics developed from modeling of evolution of genes in populations
    • Quantitative Genetics developed from modeling of inheritance of multi-factorial phenotypes
    • Important books appeared that delt with evolution and speciation (E. Mayr, T. Dobzhansky), evolution in plants (G. Ledyard Stebbins), evolution and paleontology (G. G. Simpson), and evolution and adaptation (T. Dobzhansky)
  • Molecular Biology was incorporated into Darwinian theory
    • J. Crow and M. Kimura introduced Neutral Theory of Evolution
    • wealth of discoveries about genes and genomes integrated into genetic theory
      • jumping genes, transposons, DNA duplications, epigenetic effects
  • Punctuated Equilibrium and Palentology
• Twenty-First Century Evolution
• Evolutionary Genomics
• Evolutionary Historical Ecology
• Evolutionary Developmental Biology

Last updated January 20, 2010