Evolution by Natural Selection

Pre-Darwinian Ideas

• At the time, biology was not a separate science from geology, etc… all of which were considered ‘Natural History’. Some interpreted natural history from a biblical perspective as in William Peale’s Natural Theology

• It was believed that the Earth was relatively young (6000 years old) and that species were fixed and unchanging.

Pre-Darwin Geology:Catastrophism

• Georges Cuvier helped to develop the geologic theory of catastrophism which stated that geologic change results from catastrophies like the biblical flood, etc… and that the Earth was young.

• He interpreted changes in the fossil record in this way.

Pre-Darwin Biology:Carl Linnaeus & Georges

Buffon• The Father of

Taxonomy, Linneaus, believed organisms were created and remained fixed through time. His goal was to determine the underlying order to “Gods plan”

• The French naturalist, Buffon, was effected by the Enlightment and took a more secular perspective.

Societal Change

• Most peoples position in life was static and unchanging.

• Changes in religion (reformation), government (American and French revolutions), and economy (Industrial revolution) were important societal changes that provided a new paradigm.

• This new paradigm was associated with individual rights and responsibility.

Changes in Geology

• Because of the increased need for coal and iron ore for Industrial Revolution geologist began to discover the fossils that would call into question our view of geology and life

Theory of Uniformity

• Charles Lyell• Uniformity a concept

developed by James Hutton became popular after Lyell’s publication of the Principles of Geology

• Geologic change tends to be slowly cumulative, not catastrophic, and caused by familiar forces like erosion.

Change in Biology:Charles Darwin

• A wealthy gentleman who was educated in medicine and theology, before his Voyage on the HMS Beagle.

• Used his knowledge of selective breeding (Artificial Selection) and the Malthusian Doctrine of population limits to propose a mechanism for evolution.

Darwin’s Voyage

• Sailed for 5 years around the Earth on the H.M.S. Beagle as Captain Fitzroy’s companion

• Became a secondary naturalist making observations in the Galapagos Islands

Darwin’s Natural Experience

• Unlike Linnaeus, Darwin observed living organisms within the habitats they lived, and concerned himself with more than just naming.

• He noticed differences in related species that correlated geography.

Natural Selection• Principle of Variation

Variations exists between individual members of a species that are inheritable from one generation to the next.

• Principle of OverpopulationSpecies tend to produce more offspring than can survive during any given generation.

• Principle of the Struggle for ExistenceThe environment may favors members of a species having particular variations, and those favored will pass their variations on to the next generation.

On the Origin of Species

• Alfred Wallace a biologist studying in Indonesia wrote to Darwin about natural selection

• A joint paper was arranged and presented before the Royal Society of London

• Subsequently published Origin of Species in 1859

Darwinian Deductions

• Darwinian evolution suggests that all currently living and extinct species share a distant common ancestor

• Darwinian evolution is ‘materialistic’ in that is is based purely on the empirical world and does not rely on the spiritual.

• Darwinian evolution is ‘not progressive’ in that all organism currently alive are equal in their adaptability. We are not unique or more important than other organisms.

• Similar to the Copernican Revolution in the physical sciences.

Directional Selection

• Type of selection event in which the phenotypes at one end of the continuum of variation are selected against

Disruptive Selection

• Type of selection event in which those individuals with the average phenotype are selected against

Stabilizing Selection

• Type of selection event in which individuals having the extreme phenotypes in the continuum of variation are selected against