03b - Darwin & Evidence of Evolution

Darwin & Evidence of Evolution

Charles Darwin (1809–1882)
 Naturalist and geologist who theorized evolution by natural selection. Published On the Origin of Species in 1859. Main principles: all living things are related; natural processes drive evolution.

Evidence of Evolution

  1. Comparative anatomy – body parts of very different organisms can be similar. Some structures are vestigial (retained but reduced/lost function). Homologous structures: evolved from common ancestor, similar anatomy, different function. Analogous structures: evolved independently, similar function, different anatomy.

  2. Embryology & development – embryonic similarities exist between dissimilar vertebrates. Closely related species share more similarities. Early embryonic stages show ancestral traits; later stages show modern adaptations. Examples: eyes in embryonic moles, pelvic rudiments in snakes, teeth in baleen whales.

  3. Fossil records – fossils show incremental changes over time. Radiometric dating reveals ages of layers/fossils. Older layers have simpler organisms. Transitional forms connect distant relatives (e.g., Archaeopteryx links dinosaurs to birds). Examples: horse evolution – toes fused into hoof, skull/teeth adapted for grazing. Human lineage – Toumaï (TM 266) ~7 million years old, near last common ancestor with chimps.

  4. DNA/biochemical comparisons – closely related species have more similar DNA. Evolutionary (phylogenetic) trees show branching from shared ancestors. Species that share a recent common ancestor = close cousins (e.g., humans and chimps); distant ancestor = distant cousins (e.g., humans and fish). Species are never direct parent–child.

  5. Biogeography – closely related species occur in geographically close areas. Distant species with similar features evolved under similar selective pressures. Fossil distributions align with continental drift and geological records. Examples: beaver and muskrat.

  6. Observational evidence – rapidly reproducing organisms evolve in real time. Antibiotic resistance in bacteria since 1940; viruses evolve constantly to adapt to hosts.