II. HISTORY OF THE THEORY OF NATURAL SELECTION

A. EARLY CONTRIBUTORS TO THE THEORY

1. Epicurus: Postulated that natural forces give rise to organisms of different types and that only the types able to support and propagate themselves have survived.

2. Thomas Malthus: Wrote "An Essay on the Principles of Population" in 1798.

a. contended that more children are born than reach maturity

b. factors such as food sources, disease, and war are important in the "struggle for existence"

c. these factors restrict the size of the human population

3. Charles Lyell: Noted that anyone studying the continuous changes in the earths surface "will immediately perceive that, amidst the vicissitudes [changes] of the Earth’s surfaces, species cannot be immortal but must perish one after the other, like the individuals which compose them."

4. Charles Darwin: Realized there were variations within all living species, and concluded that:

a. a "natural selection process" is in constant operation to adapt species to the changing earth

b. this selection process favors the healthiest and most fertile offspring. (Lyell disagreed.)

c. To Lyell: "you cut my throat, and your own throat; and I believe you will live to be sorry for it."

5. Alfred Russel Wallace: (1823-1913)

a. as a result of reading Malthus, came to the same conclusions as Darwin.

b. did not receive the attention of Darwin because he did not have as much documentation.

c. in 1858, Linnean Society President, Thomas Bell, concluded, "The year passed without being marked by any striking discoveries."

B. A DEMONSTRATION OF THE ORIGIN OF SPECIES BY NATURAL SELECTION

(by Wallace in his "Natural Selection and Tropical Nature", 1891)

1. Proved Fact: There is a rapid increase in organisms (at least births of organisms) but the total number of individuals remains stationary on the average.

Necessary Consequences (and thus, proved facts): There must be a struggle for existence, with the deaths equaling the births.

2. Proved Fact: Struggle for existence: There is heredity resulting in variation of individuals, or a general likeness with individual differences between parents and offspring.

Necessary Consequences (and thus, proved facts): There is survival of the fittest, (i.e., natural selection); meaning, simply, that on the whole those individuals die who are least fitted to maintain their existence. (usually because of disease or starvation)

3. Proved Fact: Survival of the fittest: There is continuous change of external conditions which is universal and unceasing (see Lyell's "Principles of Geology")

Necessary Consequences (and thus, proved facts): There are changes of organic forms, (i.e., speciation) to keep them in harmony with the changed conditions; and as the changes of conditions are permanent, the changes of organic forms must be in the same sense permanent, and thus originate new species.

C. DEFINITION OF NATURAL SELECTION

Natural selection is the process by which natural ecosystems select those gene pools (within a species) that most effectively fill niches within the changing but natural environment.

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