Evolution by Natural Selection

Pre-Darwin Widely Accepted Concepts

• Earth considered relatively young

• Species don’t evolve

• Linnaeus Classification was widely used, and was viewed as a study of divine design

Gradualism

geological features in rocks are formed via slow and continous processes

• Charles Lyell

Uniformitarianism

The same natural laws govern the natural process throughout time periods

• Charles Lyell

Jean-Baptiste Lamarck

• Species can change over time, and eventually reach perfection

• Extinction is not possible

Lamarckism

Species evolve by inheriting characteristics that are acquired through their lifetime

• Lacked supporting evidence; not considered a plausible theory

Catastrophism

God causes extinction events so that new species can occur

• George Cuvier

George Cuvier

Species don’t evolve; god created them

Richard Owen

• Species evolve

• Changes do not occur via evolutionary mechanisms; changes are ordained by divine creations

• Defined the term homology and the archetype for vertebrate

Speciation

Origin of new species diverged from ancestral species

Adaptation

Inherited characteristic of an organism that enhances its survival and reproduction in a specific environment

Unity of organisms

Similar traits due to descent from shared ancestor

Diversity of organisms

Different traits among organisms due to changes in heritable traits

Population

A group of individuals of the same species that live in the same area and interbreed to produce fertile offspring

Observations made by Darwin

• Individuals have multiple heritable traits of characters

• Populations produce more offspring than the environment can reasonably support, leading to most offspring not surviving or reproducing

  • Individuals compete for limited resources

Inferences made by Darwin

• Individuals leave more offspring, if their inherited traits give them a higher chance of surviving and reproducing

• The unequal ability of individuals to survive and reproduce would lead to accumulation of traits favored by the specific environment

Selective Pressure

Environmental and biological factors acting on populations to influence the survival and/or reproduction of individuals in the populations

Evolution

The process of organisms descending from ancestral organisms with modifications

Natural Selection

The process by which traits that enhance survival and reproduction become more common in sucessive generations of a population

Artificial Selection

Selective breeding of plants and animals to encourage the occurence of desirable traits

Selection Pressure

Environmental and biological factors that influence the survival and reproductive success of individuals within a population

• Consistent selection pressure over time leads to directional changes in phenotypes (visible characters)

• Changes in environment leads to changes in the direction and/or intensity of selection pressure

Genotype

• Genetic Makeup

• Heritable through descent from ancestor

• Variations arise randomly

Phenotype

• Expression of genetic makeup

• Influenced by environmental factors

• Inherited via modification of genotype

Phenotypic Variation

The variability in phenotypes within a population

• Determined by combination of genotype and environmental factors

  • Phenotypes influenced by environmental factors are not heritable

  • Sometimes genotype alone can determine phenotype

• Natural selection acts on phenotypes, altering the frequency of genotypes in populations

Genotypic Variation

The variability in genotypes within a population

• Arise randomly, but natural selection is not a random process