7.2 Evidence of Evolution

Darwin’s Principles of Natural Selection

1. Individuals in a population are genetically different

2. Variations can be inherited

3. Organisms have more offspring than can survive (Malthus)

4. Variations give some organisms increased reproductive success

Descent with Modification

All present life descended from previous life forms

Modification by Natural Selection

Inherited traits allow some organisms to reproduce more successfully than others of the same species

Fitness

An organisms ability to survive and reproduce

Law of Superposition

In undisturbed rock layers, the oldest rocks are at the bottom

Succession of Forms

Structures in earlier fossils become more elaborate or refined in more modern organisms

Principle of Fossil Succession

Fossil organisms succeed one another in a definite and determinable order, therefore any time period can be recognized by its fossil content

Homologous Structures

Structures on different organisms with a common origin modified for different functions (Ex. bat wing, human arm, whale flipper)

Analogous Structures

Structures on different organisms with a common function but different origins (Ex. wings of butterflies and wings of birds)

Vestigial Structures

Structures that are reduced, have a new use, or have no use; related organisms may have the same organ in fully developed and functional condition

Similarities in Embryology

Studies of early embryonic development show similarities between organisms (Ex. fish, reptiles, birds and humans all have pharyngeal arches and tails during embryonic development)

Molecular Evidence: Features Shared by All Organisms

• DNA and genetic code

• Glycolysis

• Lipid bilayer of the cell Membrane

• Ribosomes and protein synthesis

• ATP

Molecular Evidence: Similarities in Macomolecules

The more similar micromolecules are, the more closely related the species are (Ex. chromosome 2 in humans has analogs in chromosomes 12 and 13 in apes)

Biogeography

• Similar ecosystems around the world are populated by similar, unrelated species

• All remote islands have unique (endemic) forms of life

• Ex. Australia: native animals marsupials only

• Ex. Penguins: in southern hemisphere only

• Ex. Polar bears: in north pole only

Succession of Forms

The gradual change in an ecosystem’s species composition over time

Hox Genes

Control development of the body, directing an organisms body plan formation