Evolution & Natural Selection
Evolution is the change in heritable traits in a population over time. Natural selection is the primary mechanism — organisms with advantageous traits survive and reproduce more.
Darwin's Four Principles
1. Variation — individuals in a population differ.
2. Heredity — traits pass from parent to offspring.
3. Overproduction — more offspring produced than can survive.
4. Differential survival — better-adapted individuals survive and reproduce more.
Natural Selection in Action
Classic example: Peppered moths in England. Before industrialization, light moths survived better on light trees. After soot darkened trees, dark moths had an advantage and increased in population.
Adaptations
An adaptation is any trait that increases fitness (ability to survive and reproduce). Examples: giraffe long neck (reaching leaves), polar bear white fur (camouflage on snow), cactus waxy skin (reducing water loss).
Evidence for Evolution
- Fossil record — transitional forms showing gradual change
- Comparative anatomy — homologous structures (human arm, whale flipper, bat wing)
- DNA evidence — related species share similar gene sequences
- Direct observation — antibiotic resistance in bacteria
FAQ
Does "survival of the fittest" mean strongest? No — "fittest" means best suited to the current environment, not physically strongest.
Is evolution a theory or fact? Both. It's a scientific theory (well-tested explanation) supported by overwhelming evidence.
Quick Quiz
Test what you just learned. Choose the best answer for each question.