Rucete ✏ Campbell Biology In a Nutshell
Unit 4 MECHANISMS OF EVOLUTION — Concept 22.3 Evolution is Supported by an Overwhelming Amount of Scientific Evidence
Darwin’s theory of evolution is strongly supported by diverse scientific evidence from direct observations, homology, fossil records, and biogeography. Collectively, these lines of evidence convincingly demonstrate how evolution shapes life on Earth.
Direct Observations of Evolutionary Change
- Natural Selection in Response to Introduced Species: Soapberry bugs in Florida evolved shorter beaks after switching food sources. This change occurred within decades, showing rapid evolution in action.
- Evolution of Drug-Resistant Bacteria: MRSA bacteria evolved resistance to antibiotics through natural selection, demonstrating real-world evolutionary change.
Homology: Anatomical and Molecular Evidence
- Homology is similarity due to shared ancestry.
- Anatomical Homologies:
- Forelimbs of mammals (e.g., humans, cats, whales, bats) share structural similarity despite functional differences.
- Vestigial structures (e.g., pelvic bones in snakes) reflect ancestral traits.
- Molecular Homologies:
- All organisms share the same genetic code, suggesting a common origin.
- Shared genes among distantly related species support molecular-level evolution.
Evolutionary Trees and "Tree Thinking"
- Evolutionary trees depict hypotheses about relationships among species.
- Branch points indicate common ancestors; nested traits reflect descent.
- Used to infer traits and guide evolutionary research.
Convergent Evolution: Similarity Not from Common Ancestry
- Convergent evolution occurs when unrelated organisms evolve similar traits due to similar environments.
- Example: Sugar gliders (marsupials) and flying squirrels (placentals) both evolved gliding adaptations independently.
Fossil Record: Documenting Evolutionary Transitions
- Fossils show how organisms changed over time and reveal transitional forms.
- Example: Whale ancestors transitioned from land-dwelling to fully aquatic forms.
Biogeography: Geographic Distribution of Species
- Biogeography explains species locations using geographic and continental drift history.
- Fossil and species distributions match predictions made from evolutionary theory.
- Example: Related freshwater fish across continents indicate historical connections before separation.
In a Nutshell
Multiple lines of scientific evidence strongly support Darwin’s theory of evolution, including direct observations, homologies, fossil transitions, and biogeography. Together, they confirm evolution as a powerful, well-supported explanation for the diversity of life on Earth.