Chapter 8 B Biological Evolution Jean Lamarck Theory

Chapter 8 B Biological Evolution

Jean Lamarck • Theory of need • Theory of use and disuse • Theory of inheritance of acquired characteristics

Analysis of Lamarck’s Theory • Basic problem: passing on acquired characteristics to future generations

Charles Darwin Theory of natural selection The Origin of Species by Means of Natural Selection (1859)

Artificial Selection Vs. Natural Selection

Descent with Modification • Proposed that all living things descended from a single common ancestor

Survival of the Fittest • peppered moth

Analysis of Darwin’s Theory There is not always overpopulation.

Analysis of Darwin’s Theory The “fittest” do not always survive and reproduce.

Analysis of Darwin’s Theory An organism must have the gene for a certain characteristic in order for it to be produced.

Analysis of Darwin’s Theory The theory does not allow for the formation of new characteristics. It only selects for already existing traits.

Analysis of Darwin’s Theory Natural selection regroups existing characteristics. No new genetic information is created.

Later Developments in Evolutionary Theory

Hugo De Vries Species and Varieties, Their Origin by Mutation

Mutation-Selection Theory (Neo-Darwinism) • Blending of Darwin’s theory of natural selection & De Vries’ theory of mutations • Mutations supply the variations, and natural selection determines which variations survive.

Mutation-Selection Theory (Neo-Darwinism) • For evolution to occur, new genes must form. • Mutations are the only known way for this to happen. • However, mutations have not been shown to increase the amount of genetic information.

Problems with the Mutation Theory of Evolution • Mutations are random. – Scientists cannot control or predict which genes mutations will affect.

Problems with the Mutation Theory of Evolution • Mutations are rare. – It is estimated that uncorrected mutations occur once in 10 million cell divisions.

Problems with the Mutation Theory of Evolution • To be passed on, mutations must occur in the germ cells. – Mutations in somatic cells will not affect the organism’s offspring.

Problems with the Mutation Theory of Evolution • Requires “good mutations” – Must be beneficial – Mutations are either neutral or harmful.

Problems with the Mutation Theory of Evolution • Requires “good mutations” happening repeatedly – In many, many organisms all over the world – Not just unlikely. . . impossible!

Problems with the Mutation Theory of Evolution • Too many mutations will kill an organism. – Genetic load

Problems with the Mutation Theory of Evolution • The mutation theory of evolution is statistically impossible. – Mathematicians have proved that it could not have occurred, even given billions of years.

Problems with the Mutation Theory of Evolution • What about the missing links?

Punctuated Equilibrium Stephen Jay Gould The view that evolution occurred in periods or leaps of time, while at other times, no or very little evolution took place