Evolution and Natural Selection

A change in the frequency of alleles in a population over time. Populations evolve, not individuals.

1) Variation among individuals, 2) Heritability of that variation, 3) Overproduction/competition for limited resources, 4) Differential reproductive success.

Reproductive success — how many offspring an individual leaves — not strength or health. A sickly peacock with 40 chicks is fitter than a robust one with none.

A rare pre-existing mutation lets one cell survive the drug; it rebuilds the colony as 100% resistant. The antibiotic selects the mutation — it does not create it.

Homologous: same underlying structure from shared ancestry, different functions (human arm, bat wing, whale flipper). Analogous: same function, separate origins (bird wing vs. insect wing) — convergent evolution.

Reduced leftovers from ancestors that have lost their original function: human appendix, pelvic bones in whales, eye sockets in blind cave fish.

Tiktaalik (fish with wrist bones), Archaeopteryx (feathered dinosaur), and the whale series Pakicetus → Basilosaurus — all found in the correct rock layers.

The genetic code is universal; DNA similarity tracks anatomy (human–chimp ~98.8% identical); cytochrome c is nearly identical across eukaryotes.

Random change in allele frequencies, strongest in small populations — includes founder effects and bottlenecks. It is not adaptive.

Mutation, which is random with respect to need. Selection is the only mechanism that produces adaptation.