BIOL 4160

Evolution

Phil Ganter

301 Harned Hall

963-5782

Acharia (Sibine) stimulea, the saddleback caterpillar, armed with urticating spines and advertising it!

01 - The Origins of Evolutionary Questions and Theories

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General comments

Biological Evolution is not merely change in organisms

Groups of related organisms evolve, not individual organisms nor, as the book says, simply groups of organisms

Relatedness and Inheritance

Putting aside the question of the origin of life, we assume that all new organisms originate as the outcome of reproduction by organisms in the previous generation.  That is, all new organisms have a parent or parents. 

  • This assumption gives rise to the concept of relatedness - connections between organisms due to the material inheritance offspring receive from their parent or parents.
    • In biological evolution, inheritance is material but it's really more complicated than that
      • The matter (DNA and other information-rich molecules in the gametes) inherited carries information about the structure of the organism and structure is related to function
        • Because we can consider information as inherited, then information all information received from other members of the same species can also be considered an organism's inheritance
        • Social species then receive both genetic information and cultural information
  • A corollary of the idea of relatedness is the idea of distance in relations.  This arises because an organism's parent or parents have, in turn, their own parent or parents.  Relatedness connects organisms across many generations.

Darwin (and others before him) saw all life as descending from a single origin.  In this view of life, all living organisms are related, although the distance between some has grown great because the common parents they share are many, many generations in the past.

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.

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
  • Orthogenesis
  • Mutationism

Evolution today

  • Mendel represented a challenge to Darwin's gradualism
    • The Modern Synthesis - used mathematical models to show how Mendelian inheritance could give rise to gradual, Darwinian evolutionary change
  • Molecular Biology was incorporated into Darwinian theory
    • Crow and Kimura

Last updated January 15, 2009