BIO 3400 Scioli
Summer II 1999


A brief history of evolutionary thought (A much more detailed and interesting presentation of this material may be found at the University of California (Berkeley) Museum of Paleontology web site. You are encouraged to visit this site.

I. Evolution (= "unrolling" or "rolling out") is a fact, not a hypothesis nor a theory. Populations of organisms change through time just as American automobiles and women's fashions do.

  1. Plato (427 - 347 BC): developed the concept of the eidos (= "form" or "idea") an ideal form imperfectly imitated by objects and organisms in the real world. In Essentialism, only the perfect essences in the ideal world matter not the variations found among similar objects in the real world.

  2. Aristotle (384 - 322 BC): one of Plato's students; developed the concept of the Scala Naturae, or the Great Chain of life. The lowest rung on the Scala Naturae was occupied by inanimate objects; plants ranked higher and lower animals ranked higher still. More perfect creations like humans, angels and other spiritual beings occupied the upper rungs. The Great Chain of Life was perfect, had no gaps and was permanent and unchanging. Each creature had its place fixed.

  3. Creationism (Separate Creation): held that each individual species had been specially created by a Divine being who made Mankind in his image and placed us on Earth, the center of the universe. Here, too, see the influence of Plato as we were all considered imperfect but made in the perfect image of God.

  4. William Smith (1769 - 1839): from the study of fossils (= "dug up"), he observed that particular types of fossils were associated with particular strata of rock. Lower (older) strata contained many unfamiliar organisms; upper (more modern) strata contained modern forms; intermediate strata contained a progression of ancient to modern forms.

  5. Georges-Louis Leclerc, Comte de Buffon (1707 - 1788): prepared a 44-volume encyclopedia, Historie Naturelle, in which he attempted to amass everything known about the natural world. He questioned the idea that the Earth was a mere 6,000 years old and held that organisms were capable of evolutionary change. He proposed that the original creation produced a relatively small number of founding species which gave rise to modern species, although he lacked a mechanism for this change and convincing evidence of the great age of the Earth.

  6. Georges Cuvier (1769 - 1832): proposed theory of catastrophism to explain the pattern of extinction seen in fossil-bearing strata. Many scientists of his day still doubted that the Creator would allow any of his creations to be eliminated. Cuvier, who did not believe in evolution, established extinction as fact. He hypothesized that the Earth was of immense age and that periodic catastrophes eliminated some of the many species originally created. Modern species are survivors of these catastrophes and date back to the creation. He was unable to explain, however, why none of the modern forms were ever found in the oldest strata.

  7. Louis Agassiz (1807 - 1873): intellectual heir to Cuvier's ideas; he proposed a new creation after each catastrophe. This requires a complicated pattern of more than 50 catastrophes, each followed by another act of special creation! Agassiz contributed some great work with fossil fish and, more importantly, showed geologists the significance of large scale glaciation as a force shaping the Earth's surface.

  8. James Hutton (1726 - 1797): proposed theory of uniformitarianism. It was not necessary to invoke repeated global catastrophes to account for the geologic changes that shape the face of the planet. A simpler explanation utilized the slow, steady, repeating forces of nature - sedimentation, lava flows, erosion, etc. By examining the rate at which these processes work, Hutton concluded that the Earth was many millions of years old - perhaps eternal.

  9. Charles Lyell (1797 - 1875): an influential proponent of Hutton's theory of uniformitarianism. Together, Hutton and Lyell established the great age of the Earth - one of the two items Buffon lacked for his earlier ideas.

  10. Jean-Baptiste de Lamarck (1744 - 1829): proposed a mechanism for organic change (evolution). His mechanism, inheritance of acquired characteristics, was progressive and relied on Lamarck's belief that organisms possessed an innate drive toward perfection. In Lamarck's mechanism, individuals evolved and passed these changes to their offspring, e.g., the example of the giraffe's long neck. This idea did not stand the test of time but, at least, prepared thinking people to consider the possibility that organisms could evolve.

  11. Charles Darwin (1809 - 1882): proposed a different mechanism for evolutionary change, natural selection. Darwin, a recent graduate of Cambridge, was selected to serve as the naturalist during the five-year surveying expedition of the H.M.S. Beagle (1831-1836). The Beagle sailed to South America and around the world from there. Some of his greatest insights, years after his return, came from observations he made during a visit to the Galapagos Islands. His plan for a huge volume documenting his proposed mechanism of evolutionary change was short-circuited when he received word from Wallace of a similar, independently-conceived idea. The joint publication of Darwin's and Wallace's papers in 1858 was followed by Darwin's publication of On the Origin of Species the following year. More information about Charles Darwin

  12. Alfred Russel Wallace (1823 - 1913): independently came up with the idea of natural selection which he promptly sent to Darwin.

II. The Darwinian revolution began in 1859 with the publication of On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. This revolution was marked by the existence of a testable, scientific hypothesis - natural selection as the mechanism of change. The rediscovery of Mendelian genetics in 1900, and the initial development of the mathematical theory underlying population genetics in 1908 paved the way for the Modern Synthesis. The Neo-Darwinian theory which resulted drew from and reconciled genetics, systematics and paleontology. Ernst Mayr has called the concept of evolution "the greatest unifying theory in biology." Similarly, Theodosius Dobzhansky has stated that "Nothing in biology makes sense, except in the light of evolution."

Natural selection requires only that

  1. Phenotypic variation for some trait exists among members of a population.
  2. This phenotypic trait must be adaptive, i.e., affect fitness [measured as the number of surviving offspring]. Individuals with some forms of this phenotypic trait gain fitness advantages because of it; individuals with other forms of this phenotypic trait suffer losses in fitness.
  3. This phenotypic trait must be heritable, i.e., under genetic control.
  4. Although not required for natural selection to proceed, the birth of more offspring than can be supported by the available resources can greatly speed the action of natural selection. This idea was inspired by Darwin's reading of Thomas Malthus' Essay on Population.

III. Evidence for evolution

  1. Fossils
  2. Comparative anatomy
    1. homologous structures
    2. analogous structures / convergent evolution
    3. vestigial structures
  3. Comparative embryology
  4. Comparative biochemistry
  5. Artificial selection - if artificial breeding could result in such dramatic changes in a few hundred years or less, then what could natural selection change given the 4.5 billion year age of the Earth?
    1. single species of wolf-like ancestor (Canis lupus)--> all dog varieties (fully interfertile)
    2. single species ancestral plant species --> broccoli, cauliflower, kohlrabi, cabbage, Brussels sprouts, kale (fully interfertile varieties of same species)

IV. Examples of present day evolution

  1. Peppered moth (Biston betularia) before, during and after the Industrial Revolution in Great Britain.
  2. Checkerspot butterfly switching between 1983 and 1993 from dependence on native Collinsia to dependence on introduced Plantago species for oviposition.
  3. Change in Florida cockroaches from glucose-loving to glucose-averse due to Combat® baits.

V. Scientific method for those who may have forgotten (or never learned) it

  1. The scientific method is based on a small set of assumptions
    1. all events can be traced to natural causes
    2. natural laws that govern events apply everywhere and for all time
    3. people perceive natural events in similar ways
  2. Components of the scientific method
    1. observation of a specific phenomenon
    2. formulation of a hypothesis (or hypotheses, plural); the hypothesis is an educated guess
    3. experimentation to test the hypothesis
    4. conclusion that
      1. hypothesis is valid, i.e., it is supported by the data or
      2. hypothesis is invalid, i.e., it is not supported by the data and is
        1. discarded or
        2. revised
  3. Differences from other ways of knowing
    1. scientific experimentation attempts to isolate a single variable to be tested
    2. scientific experimentation employs a "control" group for comparison
    3. scientific conclusions are always held tentatively and are always subject to revision or rejection based on newer, valid experimental data

VI. Concluding remarks

  1. Simple recorded observation is still a powerful tool for science.
  2. Great scientific discoveries are seldom the work of one person. They tend to be based on an accumulation of data and ideas contributed many investigators, over a long period of time. As Sir Isaac Newtom is often quoted, "If I have been able to see farther than others, it was because I stood on the shoulders of giants."

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