01Lines of evidence
Fossils show change over time, dated by radiometric dating and rock layers (transitional forms like Tiktaalik).
Homologous structures — same bones, different functions (human arm, whale flipper, bat wing) — reveal common ancestry. Vestigial structures (whale pelvis, human appendix) are leftovers.
Molecular evidence: comparing DNA and protein sequences (like cytochrome c) — fewer differences = closer relationship. Embryology: related vertebrates share pharyngeal pouches and tails as embryos.
Biogeography: related species cluster geographically (Galápagos finches).
02Notebook box
Strongest modern evidence: molecular sequence similarity.
Worked example: Species A and B differ by 2 amino acids in a protein; A and C differ by 15. Which pair shares the most recent ancestor? → A and B.