← Back to home
🦖
Survival of the best fit
Evolution & Natural Selection
Populations evolve. Individuals don't. Variation + environment = change over time.
🔁 The 4 steps of natural selection
1
Variation
Individuals in a population differ (mutations + sexual reproduction).
2
Competition
More offspring than resources → struggle to survive.
3
Survival
Best-fit traits survive in the current environment.
4
Reproduction
Survivors pass traits to offspring → trait spreads over generations.
🚨 Top trap: Individuals don't evolve. Populations do.
A giraffe doesn't grow a longer neck because it stretches. Giraffes with longer necks survived & reproduced more — over many generations the population's average neck length increased.
🌡️ Environment simulator
Survives ✓
🐻❄️ Thick fur
Disappears ✗
🐻 Thin fur
Insulation matters. The environment doesn't create the trait — it selects from existing variation.
🦴 Evidence for evolution
Fossils▾
Show change over time and transitional forms (e.g., whale ancestors with legs).
Homologous structures▾
Same bone layout, different uses (human arm, bat wing, whale flipper) → common ancestor.
DNA similarities▾
More similar DNA = more closely related.
Embryology▾
Early embryos of vertebrates look similar — shared ancestry.
🎯 Quiz yourself
Evolution · QuizQ1 / 4