Darwinian Evolution

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Darwinian Evolution
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Intersting explanation of natural selection -Real Player

Darwin's Basic Premise

Darwin's On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, made several points that had major impact on nineteenth-century thought:

1.That biological types or species do not have a fixed, static existence but exist in permanent states of change and flux;
2.that all life, biologically considered, takes the form of a struggle to exist -- more exactly, to exist and produce the greatest number of offspring;
3.that this struggle for existence culls out those organisms less well adapted to any particular ecology and allows those better adapted to flourish -- a process called Natural Selection;
4.that natural selection, development, and evolution requires enormously long periods of time, so long, in fact, that the everyday experience of human beings provides them with no ability to interpret such histories;

5.that the genetic variations ultimately producing increased survivability are random and not caused (as religious thinkers would have it) by God or (as Lammarck would have it) by the organism's own striving for perfection.

The effect of all these points was to move man away from the center of creation and imply that God could hardly be nature's driving force. These are direct quotes from Darwin's book Origin Of The Species, in which he outlines his theory.

1. The struggle for existence: Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult -- at least I have found it so -- than constantly to bear this conclusion in mind. Yet unless it be thoroughly engrained in the mind I am convinced that the whole economy of nature, with every fact on distribution, rarity, abundance, extinction, and variation, will be dimly seen or quite misunderstood. We behold the fact of nature bright with gladness, we often see superabundance of food;we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life. . . . I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny. . . . As more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms (Chapter 3, "Struggle for Existence").
2. Darwin's emphasis upon abundance (and his use of metaphor): In looking at Nature, it is most necessary to keep the foregoing considerations always in mind -- never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount. The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force (Chapter 3).
3. (A) Adaptation for survival; (B) Relation in opposition: The structure of every organic being is related, in the most essential yet often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has to escape, or on which it preys. This is obvious in the structure of the teeth and talons of the tiger; and in that of the legs and claws of the parasite which clings to the hair on the tiger's body. But in the beautifully plumed seed of the dandelion, and in the flattened and fringed legs of the water-beetle, the relation seems at first confined to the elements of air and water. Yet the advantage of plumed seeds no doubt stands in the closest relation to the land being already thickly clothed by other plants; so that the seeds may be widely distributed and fall on unoccupied ground. In the water-beetle, the structure of its legs, so well adapted for diving, allows it to compete with other aquatic insects, to hunt for its own prey, and to escape serving as prey to other animals (Chapter 3). 

 

                                               

 

David Lindsay
dwlindsay@mail.utexas.edu