Background Info on Theory of Evolution

before chapter 7

prevailing thoughts @ time when darwin’s evolution theory was published

1. static (stable) unchanging universe
2. causes of phenomena were purposeful (deity)

natural selection

some individuals contribute more offspring to next generation than others

adaptation

apparent good fit to environment

“nothing in biology makes sense except in the light of evolution”

Theodosius Dobzhansky

greek essentialism

variation observed was simply the imperfect copies of the transcendental ideal form of the essence; the ideal is perfect and unchanging (i.e. triangles all have 180 degrees despite variation in triangles)

concept of plentitude

eternal, unchanging essense of all things exist in God’s mind. God is perfect, so everything He created must be perfect, so no extinction (implies perfection)

scala naturae or great chain of being

changes in this scale are unnatural, applies to social classes also. Rule by Devine Right

reformation ideas

1. humans the reason for and center of the universe
2. universe NOT static and IS changing

evidence for change in universe vs. static universe

* volcanos
* earthquakes
* sedimentary rocks
* marine fossils on mountain tops
* fossils of extinct forms

catastrophism

successive catastrophes (great floods, etc.)

gradualism

slow change in small steps

uniformitarianism

physical processes at present same as in the past; land forms produced by same physical processes

principle of geology

Charles Lyell

Jean-Batiste de Lamarck

* lineages of organisms exist indefinitely
* no branching, no extinction
* proposed 2-part mechanism = internal forces and inheritance of acquired traits

internal forces

unknown internal mechanism causes differences between parent and offspring

inheritance of acquired traits

use or disuse of trait alters trait through lifetime, which is then passed to offspring (i.e. giraffe’s neck)

The Origin of Species

1. descent with modification
2. mechanism for the evolutionary processes

descent with modification

* explains diversity and unity of life
* all organisms are related through descent from a common ancestor that lived in the past
* implies that relationships among organisms can be represented by a branching tree

(darwin’s) mechanism for the evolutionary process

adaptation by natural selection

two fighting schools of thought

1. mendelains - discontinuous variation
2. biometricians - contineous variation

R.A. Fisher

“The Genetical Theory of Natural Selection” 1930

J.S.S. Haldane

“The Cause of Evolution” 1932

Sewall Wright

demonstrated that natural selection could work on all observed variation and Mendel’s Laws

Neo-Darwinism

evolution = heritable variation & selection