Why I am an evolutionist, part 1

Darwin: Evolution by means of natural selection

(Written partly in response to Jamie Kiley.)

Charles Darwin identified a mechanism by which species could change, but the explanation he devised was partial.

The theory of evolution received impressive confirmation from a later generation of scientists. They identified the other part of the evolutionary mechanism, completely unknown to Darwin.

The mutability of species

Darwin was not the first to theorize that species could change. Before Darwin was born, the Compte de Buffon had written, “all animals are come from but one animal, which, in the succession of eras … has produced all the races of animals that now exist.”1

A little later, Jean Baptiste Lamarck made the first serious attempt to explain the mechanism by which species change:  he proposed that characteristics acquired over the lifetime of an animal could be passed on to succeeding generations.

The classic example, usually cited to illustrate this idea of Lamarck’s, is the giraffe, which, by repeatedly stretching its neck to get at the tender leaves at the tops of acacia trees, actually manages to develop a longer neck during its lifetime. …

[This acquired characteristic] would show up in a slightly longer-necked offspring which, during its life would also be a neck stretcher and bequeath a still longer neck, and so on, resulting finally in the otherwise inexplicable creature that now roams the African veldt.2

Lamarck’s theory didn’t hold water. Scientists falsified it by chopping the tails off mice and then breeding them. The next generation of mice had normal tails; characteristics “acquired” by one generation were not passed on to the next.

Natural selection

Still, Buffon and Lamarck had already put together a theory of evolution. Why is the theory attributed to Darwin and not to them? Because Darwin came up with a better explanation of the mechanism by which species change.

Darwin recognized that life in the wild is a constant struggle to survive. (Actually, he learned this from another of his predecessors, Malthus.)

In a competitive world, those with the “best” characteristics — bigger, stronger, smarter, more sexually aggressive — will live longer and produce more offspring. The characteristics which gave them a competitive advantage

will probably be inherited by their offspring. This unequal survival rate, where the “good” end up outnumbering the “less good,” is natural selection.

… The process of natural selection, if carried far enough and long enough, will produce marked changes in a population and will lead eventually to the emergence of new species.3

Animals can be modified over generations by carefully controlled breeding, of course. But Darwin had explained how such changes could occur in nature (where breeding is not directed toward a desired objective).

A mystery Darwin left unsolved

Darwin’s explanation was incomplete, and he knew it. What was the biological mechanism for it?

Insofar as children resemble their parents, how are new variations ever introduced? Insofar as children do not resemble their parents, how are advantageous characteristics (e.g., smarter) passed on from one generation to the next?

Darwin broke his lance on variation. In his book he looked at it from every imaginable angle. He measured it, weighed it, tracked it, but he could not explain it. … The answer to that enormous question of how it happened was locked up inside the cell and was destined to remain locked there until the next century.4

Darwin built on the discoveries of his predecessors, and he bequeathed unanswered questions to his successors.

more to follow …

~~~~~~~~~~~~~

1Quoted in Blueprints: Solving the Mystery of Evolution, by Maitland Edey and Donald Johanson, p. 14. This is an excellent introductory text for anyone who, like myself, lacks a background in science.

2Ibid., p. 24.

3Ibid., p. 60.

4Ibid., p. 92.

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3 Comments (+add yours?)

  1. Jamie
    Nov 19, 2006 @ 16:47:45

    I’m looking foward to the next installment of this series, as this issue of precisely HOW new characteristics could arise is one of my major sticking points with evolution. (Actually, that’s one point I plan to address in part three of my own series on evolultion).

    Anyway, I’ll be interested to see part 2. 🙂

    Reply

  2. Stephen
    Nov 28, 2006 @ 20:10:35

    It took me longer than I planned, Jamie, but the new installment is finally up!

    Reply

  3. Trackback: Can Governments Cause a Darwinian Backslide? « The Report Card

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