Evolutionary Biology — Life Changes Over Time
EVOLUTION is the process by which species CHANGE over generations. Charles Darwin and Alfred Russel Wallace independently proposed the mechanism in the 1850s: NATURAL SELECTION. Variations within a population are inherited; some help survival and reproduction, so they become more common over generations. Over millions of years, this produces all the diversity of life.
Natural selection in 4 conditions. (1) VARIATION within a population (no two individuals are identical). (2) HERITABILITY — traits pass to offspring through DNA. (3) DIFFERENTIAL SURVIVAL/REPRODUCTION — some traits help in the environment. (4) TIME — over many generations, helpful traits become more common; harmful ones fade. Note: evolution doesn't have a goal. It's blind, statistical, and ongoing.
A pesticide kills 99% of an insect population. The 1% with a resistance mutation survive and reproduce. After several generations, most insects are resistant. This shows:
Evidence for evolution. (1) FOSSIL RECORD — older rock layers contain simpler organisms; complexity increases over time. (2) COMPARATIVE ANATOMY — homologous structures across species. (3) DNA — closely related species have more similar DNA. (4) BIOGEOGRAPHY — island species often resemble nearest mainland species. (5) DIRECT OBSERVATION — antibiotic resistance, peppered moths, Galapagos finches all show evolution happening now. The evidence is overwhelming and from multiple independent fields.
Trace a Trait
Pick a trait of an animal (giraffe necks, cheetah speed, peacock feathers). Describe how natural selection might have produced it. What variation existed? What advantage did the trait give? How did it spread? (Avoid teleological language — animals don't evolve "in order to" do something. They evolve BECAUSE traits affect survival and reproduction.)
Evolution is one of the most well-tested ideas in science. It's also one of the most beautiful — explaining the unity AND diversity of all life on Earth, including us.
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