The idea that things could slowly change over time was once not widely believed.

Increased need to explain biological diversity, vestigial features and extinction (i.e. fossil record).

Early Evolutionary Theory

1809 - Lamarck's Theory of Acquired Characteristics

1) All organisms had the ability to become more complex in structure.
2) Organisms could change in response to their environment by acquiring characteristics.
3) Acquired characteristics could be passed to offspring.

Darwin and Natural Selection

Naturalist on H.M.S. Beagle's 5 year expedition to South America and the South Pacific. Observed and collected many specimens, examined fossils, and examined many geologic features.

1859 - Darwin's Theory of Natural Selection

1) Variations in organisms of the same population (i.e. traits).
2) Organisms produce more offspring than actually survive.
3) Competition for resources in environment.
4) Individuals with advantageous variations survive an pass their traits to their offspring.

Natural Selection causes the number of individuals with favorable variations to increase over many generations until eventually species change.

Process of Evolution

Natural Selection Observed

Pepper moths of the English countryside

Speciation - Natural selection acts upon two groups of individuals until enough genetic changes occur to the point where they can no longer mate to produce fertile offspring.

Can happen via geographic isolation or reproductive isolation (ex. Abert and Kaibab squirrels)

Adaptive Radiation - New species evolve from single ancestral species due to new environment (ex. Galapagos finches).

Convergent Evolution - Environment selects similar adaptations in unrelated species (ex. wings of birds, bats, and butterflies).

Stabilizing Selection - Maintains characteristics that enable organisms to be successful its environment.

Pace of Evolution

Gradual Path vs Punctuated Equilibrium