Syllabus

CPSP118G Spring Semester: Earth, Life & Time Colloquium

Charles Darwin and the Discovery of Evolution

Thomas R. Holtz, Jr.

Charles Robert Darwin (1809-1882)

Childhood and Education:

The Voyage

Darwin's Professional Life

So, What Did Darwin & Wallace Discover?
Their model was called Natural Selection, and was analogous to "artificial selection" (e.g., domestication). Darwin and Wallace's observations:

Thus, IF some variation gives the individual a slight advantage (bigger, stronger, smaller, smarter, less tasty, whatever) at surviving; and IF that variation is heritable; THEN there is a somewhat better than average chance that organisms with that variation will survive to bear the next generation. Over the long expanse of geologic time, the accumulation of these variations will change the population from one form to another: the origin of species.

Or, to use Darwin's own words (from the Introduction to the first edition of the Origin: "As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently occurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form"

Hence,

* Natural Selection is the differential survival and reproduction of variants in a population resulting in a net change in phenotype of the descendants. *

(Short form: "Natural selection is the differential survival and reproduction of variants in a population.")

(Even shorter form with a 20th Century slant: MUTATION PROPOSES, SELECTION DISPOSES)

If Evolution can be summarized as "no one is identical to their parents", then Natural Selection can be summarized as "no one is identical to their siblings, either; plus, life's hard!"

Key points of Natural Selection:

"Survival of the Fittest"?: Not as such. Phrase not in the earlier editions of the Origin, nor was it coined by Darwin. Comes from economist/philosopher Herbert Spencer:

Some things Evolution and Natural Selection are NOT:

Scientific Reactions to Darwin and the Origin
In the late 19th Century, many parts of Darwin's work were accepted:

On the other hand, while some (Thomas Huxley, Joseph Hooker, O.C. Marsh, etc.) accepted Natural Selection, many others did not. In part they thought it could not create entirely new morphologies, but mostly because they accepted Lord Kelvin's incredible short (and inaccurate) time scale. With (for example) only 3 million years for all the Cenozoic Era, it would be hard for Natural Selection to produce the vast diversity of modern mammals.

Darwin died without knowing the mechanism by which variation was generated and passed on: genetics. (Trivia time: he actually had a copy of Mendel's work at his desk, but he had never gotten around to opening it!). Gregor Mendel's genetic work only became well-known and studied in the 20th Century. By the mid-20th Century, new discoveries in genetics, paleontology, ecology, and statistics led to the New Synthesis: a model demonstrating that Natural Selection is indeed a major force in evolution.

However, there is more to it than that. Stay tuned...

"Darwinism"
Some of the things that come out of Darwin's work:

  • Convergence: Some adaptations are mechanically advantageous and easy to produce developmentally. Different lineages of organisms can independently develop some of the same features, even though ancestors were quite different (i.e., streamlining in sharks, tunas, ichthyosaurs & dolphins).
  • Co-evolution: Selection of one species due to activity of an interactor leads to counter-selection in response of the first species
  • Living Fossils: Species do not have a fixed duration, but will persist until the evolve into something else and/or go extinct. In some cases, species (or genera) may persist for extremely long periods of time with no major changes.
  • Exaptation: Formerly called "preadaptation", the co-option of a structure that previously had some entirely different function for a new use. Seems to be the more common pattern of evolution than the appearance of entirely novel structures. For example, the wings of birds and bats were initially arms and hands; the mouthparts of various arthropods were legs; etc.

    Here is Carl Sagan's summary of Darwinian evolution and the Tree of Life, from the TV series Cosmos:

    And here is another summary of evolution and how it works (and how it ISN'T like the parody-version of evolution which Creationists claim scientists believe):

    Last modified: 6 April 2009