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 from the native balloon vine to the introduced golden rain tree. Researchers found rapid evolutionary changes occurred within decades, showing natural selection in action.
Evolution of Drug-Resistant Bacteria:
Antibiotic-resistant bacteria, like methicillin-resistant Staphylococcus aureus (MRSA), evolved quickly due to natural selection favoring resistant variants.
Resistance emerges rapidly after antibiotics are introduced, highlighting the speed and real-world consequences of evolutionary processes.
Homology: Anatomical and Molecular Evidence
Homology is similarity resulting from common ancestry.
Anatomical Homologies:
Mammals' forelimbs (e.g., humans, cats, whales, bats) share the same bone structures despite different functions, reflecting common ancestry.
Vestigial structures, such as remnants of pelvis and leg bones in snakes, indicate past functional structures inherited from ancestors.
Molecular Homologies:
All organisms share a universal genetic code, indicating common ancestry.
Similar genes among distantly related organisms provide molecular evidence for evolution.
Evolutionary Trees and "Tree Thinking"
Evolutionary trees represent hypotheses about evolutionary relationships.
Each branch point indicates a common ancestor; homologous traits form nested patterns reflecting evolutionary history.
These trees clarify relationships and predict characteristics of organisms, guiding research and understanding of evolutionary processes.
Convergent Evolution: Similarity Not from Common Ancestry
Convergent evolution leads to similar adaptations in unrelated species due to similar environmental pressures.
Example: Sugar gliders (marsupials) and flying squirrels (placentals) independently evolved similar gliding structures.
Fossil Record: Documenting Evolutionary Transitions
Fossils demonstrate that past organisms differ significantly from modern ones and document the evolution of new groups.
Example: Fossil evidence shows cetaceans (whales, dolphins) evolved from terrestrial ancestors, transitioning from land mammals to fully aquatic organisms.
Biogeography: Geographic Distribution of Species
Biogeography studies species distributions influenced by continental drift and geographic separation.
Predictive power of biogeography:
Fossils support predictions based on evolutionary relationships and continental drift, confirming evolutionary theory.
Example: Closely related freshwater fish separated by oceans evolved when continents were connected, explaining current distributions.
In a Nutshell
Multiple lines of scientific evidence strongly support Darwin’s theory of evolution, including direct observations of evolution, anatomical and molecular homologies, fossil transitions, and biogeographic patterns. This evidence solidifies evolution by natural selection as a robust and well-supported scientific theory.