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The Darwinian Revolution

Who influenced Charles Darwin?

People already knew about artificial selection (humans breeding animals and plants for desired characteristics). Darwin thought: Should nature not operate in a similar way?

The stage was set for the Darwininan Revolution!

Voyage of the Beagle

1809 - Charles Robert Darwin was born in Shrewsbury, England. From the beginning, he loved bugs n slugs, and spent most of his time outside or reading nature books.

His father, a well-known physician, thought that no good life could await a naturalist, and so sent young Charles, at the age of 16, off to the University of Edinburgh medical school. Young Charles hated med school, and dropped out after making mediocre grades.

With his father's blessing, he enrolled at Christ College at Cambridge University with plans to become a clergyman. (This isn't as odd as it sounds, since most scientists of his day were members of the clergy.)

He fell in with the biologists and became the star pupil of The Reverend John Stevens Henslow, Professor of Botany.

1831 - With the help of Darwin's uncle, Henslow convinced both Captain Robert Fitzroy of the H.M. S. Beagle and Darwin's father to let Charles go on the five year voyage as an "unpaid gentleman scholar and naturalist" and learned companion for the captain.

So at the age of 22, Darwin set sail. While the Beagle's crew mapped South American coastlines, he went ashore and collected every living things he could lay his hands on.

1836 - Darwin returned to England, settled down, married his cousin, Emma, and proceeded to write.

Musing over the years, he came to visualize the evolution of life as a spreading tree, with an ancestor at the base and the descendant species represented as the branches.

He termed this gradual change of one species into another descent with modification. What he surmised in his study, we now know from both the fossil record and studies of extant species. For example, the evolution of modern elephants and their relatives.

Darwin made profound observations, from which he inferred brilliant conclusions.

  • inference #1: The production of more individuals than the environment can support leads to a "struggle for existence," with only a fraction of offspring surviving in each generation.

  • inference #2: Survival in this "struggle for existence" is not random, but depends, in part, on the hereditary makeup of the survivors. Those individuals who inherit characteristics that allow them to best exploit their environment are likely to leave more offspring than individuals who are less well suited to their environment.

  • inference #3: Unequal reproduction between suited and unsuited organisms will eventually cause a gradual change in a population, with characteristics favorable to that particular environment accumulating over the generations.

    The Theory of Evolution by Means of Natural Selection can be broken down into four basic tenets, or ideas

    Lyell to the Rescue

    Charles Lyell and a colleague presented both Wallace's and Darwin's work at the meetings of the Linnaean Society of London on July 1, 1858. Though Wallace's and Darwin's ideas were identical, Darwin's had been written first, and more completely than Wallace's. Today, Darwin is given credit as the Father of the Theory of Evolution by means of Natural Selection, though Wallace is always given a respectful footnote.

    (To give Americans a bit of historical connection, Abraham Lincoln became president three years later, in 1861. Darwin lived quite a bit longer than Lincoln did.)

    "Survival of the Fittest"

    The phrase "survival of the fittest" was coined, not by Darwin, but by social philosopher Herbert Spencer, who was drawing an analogy between Darwin's ideas and his own hypotheses about the dynamics of economics. He wrote:

    In reality, the phrase "survival of the fittest" does not begin to describe the complexity of natural selection, and this term generally is not used in modern biology, lest it confuse the true meaning of natural selection.

    A Darwininan evolutionary biologist might consider the phrase "survival of the fittest" to mean survival of the individual leaves the most offspring, or the survival of a gene that successfully is passed on to successive generations of its carriers. But note:

    See "Evolution and Philosophy: A Good Tautology is Hard to Find" by John S. Wilkins.

    Unfortunately, Darwin's idea has sometimes been conscripted by social Darwinists who used it to sanction ruthless economic policies such as laissez faire economics.

    Natural Selection: At What Level?

    Natural selection results in differential reproduction among individuals in a population.

    Any trait (= character) exhibited by an individual may be

    The adaptiveness of a trait is largely determined by the environmental context of the individual bearing that trait. The individual will have greater or lesser success depending on its relative ability to

    But consider: Phenotype is the product of multiple gene interactions and environmental influence.

    Hence, natural selection is more complex than simple "survival of the fittest" (whatever that means).

  • Microevolution is defined as genetic change in a population from one generation to the next.

  • Macroevolution is defined as evolutionary change occurring above the species level: the evolution of new species from ancestral species, and the evolution of major taxa from common ancestors.

    But at what level is natural selection really occurring?

    The Immortal Gene

    Just for a moment, let's anthropomorphize our little friends, the genes.

    We do this with the understanding that genes don't actually think and don't have conscious motives. But we can consider the results of generations of inheritance more easily if we understand that the end result of adaptive evolution (i.e., production of a population of organisms well suited to their environment) is a product of differential inheritance of "competing" alleles of particular genes.

    Differential survival (inheritance) of competing alleles will result in increased frequency of those alleles that promote their own propagation by producing (or contributing to) adaptive phenotypic traits. This is the essence of the concept of gene-centered evolution fully described by Dr. Richard Dawkins in his 1976 book The Selfish Gene.

    No, of course genes don't work like that.

    A "selfish gene" isn't selfish, nor does it encode a "selfishness" trait in the individual carrying it.

    But a "selfish" gene does have evolutionary consequences that serve its own implicit "interest" (quotes used here to emphasize that genes do not actually have free will or though processes) in being replicated and, if possible, being immortal.

    Oddly enough, a gene's "best interest" may not coincide exactly with what one might (subjectively) consider in the best interest for its host.

    Can you think of some widespread traits in any species that seem to be crazy bad for the individual expressing them?

    Still, if the gene's manifestation causes it to be passed on to the next generation...mission accomplished.

    Language Police

    You will sometimes hear people use the terms "evolutionist" or "Darwinist", usually in a disparaging manner. These terms imply that evolution is an ideology. It is not.

    Be careful and precise in your terminology.

    Evolution: "Just a Theory"?

    You will sometimes hear people say that even scientists agree "Evolution is only a theory."

    Some people may also ask, "Do you believe in evolution?"

    For the student of natural sciences, there is a simple and appropriate response to such a question.

    The "Only a Theory" argument is flawed in that it fails to separate two important things:.

    Darwin's conclusions are based on observable evidence, and subject to the scientific method.

    In summary

    Be sure to understand that there are many misconceptions about natural selection, and that you are responsible for knowing what's correct.