The Revolutionary Idea of Evolution

Do we not therefore perceive that by the action of the laws of organization . . . nature has in favorable times, places, and climates multiplied her first germs of animality, given place to developments of their organizations, . . . and increased and diversified their organs? Then. . . aided by much time and by a slow but constant diversity of circumstances, she has gradually brought about in this respect the state of things which we now observe. How grand is this consideration, and especially how remote is it from all that is generally thought on this subject!

History of Evolution:

The idea of evolution goes back to Jean Lamarck in the early 1800's. Lamarck published a theory of evolution in 1809. Lamarck thought that species arose continually from nonliving sources. These species were initially very primitive, but increased in complexity over time due to some inherent tendency. This type of evolution is called orthogenesis.

Lamarck proposed that an organism's acclimation to the environment could be passed on to its offspring. For example, he thought proto-giraffes stretched their necks to reach higher twigs. This caused their offspring to be born with longer necks. This proposed mechanism of evolution is called the inheritance of acquired characteristics. Lamarck also believed species never went extinct, although they may change into newer forms.

All three of these ideas are now known to be wrong, but were not held as wrong at the time.

Even when resources are plentiful, the size of a population tends to increase geometrically until the population outstrips its food supply. This led Malthus to believe that poverty, disease, and famine was a natural and inevitable phenomenon, leading to a "struggle for existence". And to a large part, this proposition is borne out by the 1000-1650 population data.

Evolution came of age as a science when Charles Darwin published "On the Origin of Species." Darwin's contributions include hypothesizing the pattern of common descent and proposing a mechanism for evolution -- natural selection.

In Darwin's theory of natural selection, new variants arise continually within populations. Past experience with this class shows that this concept is not understood, but its at the essence of Darwinian selection. We will be doing laptop simulations to demonstrate this basic point.

A small percentage of these variants cause their bearers to produce more offspring than others. These variants thrive and supplant their less productive competitors. The effect of numerous instances of selection would lead to a species being modified over time.

To quote from Darwin:

To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.

Darwin also recognized several critical factors that are gleaned from careful observation :

• Variability exists within species

• Variant traits may be inherited [Darwin did not, however, know how.]

• From Malthus' principle of overproduction, many individuals must often die or fail to reproduce. In this "struggle for existence", variants that were slightly better suited to the environment would be more likely to survive.

  Big Damn Digital Post It Note:

  Darwin Never Said Survival of the Fittest

  
  
  Others interpereted Darwin's theory in this manner. To wit,

  This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called "natural selection, or the preservation of favoured races in the struggle for life.

  What is the social implication of this?

Critisicm of Darwin's Theory Read this outside of class.