Evidence of Evolution and Common Ancestry

Primary sources of evidence for evolution

• The fossil record

• Comparative morphology

• Biogeography

Fossils

Remains or traces of past organisms

Fossil record

Gives a visual evolutionary change over time

• Fossils can be dated by examining the rate of carbon 14 decay and the age of rocks where the fossils are found

• Gives geographical data for the organisms found

Comparative morphology

Analysis of the structures of living and extinct organisms

Homology

Characteristics in related species that have similarities even if the functions differ

• Embryonic homology

• Vestigial structures

• Molecular homology

Embryonic homology

many species have similar embryonic development

Vestigial structures

Structures that are conserved even though they no longer have a use

• ex) tailbone and appendix in humans

Molecular homology

many species share similar DNA and amino acid sequences

Homologous structures

Characteristics that are similar in two species because they share a common ancestor

• ex) arm bones of many species

Convergent evolution

Similar adaptations that have evolved in distantly related organisms due to similar environments

Analogous strucutres

Structures that are similar but have separate evolutionary origins

• ex) wings in birds vs bats vs bees

Common ancestry in eukaryotes

Structural evidence indicates common ancestry of all eukaryotes

• Cellular examples

  • Membrane-bound organelles

  • Linear chromosomes

  • Introns in genes

Biogeography

The distribution of animals and plants geographically

• ex) species on oceanic islands resemble mainland species