Pocket Notes — Evolution

Timelines

• Big Bang: ~13.7 bya
• Earth formed: ~4.5 bya
• First life: ~3.5 bya
• First eukaryotes: ~1.5 bya
• First multicellular life: ~800 mya
• Fish: ~500 mya · Amphibians: ~350 mya · Reptiles: ~300 mya
• Mammals: ~200 mya · Birds: ~150 mya
• Dinosaurs extinct: ~65 mya
• Homo sapiens: ~200,000 ya · Agriculture: ~10,000 ya

Milestone experiments

• Miller & Urey (1953) — CH₄, NH₃, H₂, H₂O + spark → amino acids.
• Oparin & Haldane hypothesis (abiogenic origin).

Definitions

• Evolution — change in gene frequency over generations.
• Homologous — same origin, different function (divergent evolution).
• Analogous — different origin, same function (convergent evolution).
• Vestigial — organs that lost function.
• Adaptive radiation — one ancestor → many species filling different niches.

Types of similar structures

Type	Origin	Function	Example
Homologous	Same	Different	Human arm, whale flipper, bat wing
Analogous	Different	Same	Butterfly wing vs bird wing
Vestigial	Once functional	None now	Appendix, wisdom teeth

Hardy–Weinberg equilibrium

• p + q = 1 and p² + 2pq + q² = 1
• Homozygous dominant = p², Heterozygous = 2pq, Homozygous recessive = q²
• No evolution if: no mutation, no migration, no drift, no selection, random mating, large pop.

Evolutionary forces (memorise 5)

1. Mutation
2. Recombination
3. Genetic drift (bottleneck, founder)
4. Natural selection
5. Migration / gene flow

Types of natural selection

Type	Effect	Example
Stabilising	Favours mean	Human birth weight
Directional	Shifts toward extreme	Industrial melanism
Disruptive	Favours both extremes	Galapagos finches (large & small beaks)

Speciation modes

• Allopatric — geographical isolation
• Sympatric — no barrier (polyploidy in plants)

Human evolution snapshot (increasing brain size, decreasing age)

Species	When (mya)	Brain (cc)	Note
Dryopithecus / Ramapithecus	15	—	Ape ancestors
Australopithecus	4	~500	Bipedal, Africa
Homo habilis	2	650-800	First stone tools
Homo erectus	1.5	900	Used fire
Homo neanderthalensis	0.1	1400	Buried dead
Homo sapiens	0.05-0.2	1350	Modern human

Darwin's finches — variables

Different beak types in Galapagos → adaptive radiation → example of natural selection.

Frequently asked

• Miller & Urey demonstrated what? — Abiotic synthesis of amino acids.
• Homologous or analogous: bird wing & bat wing? → Homologous (same origin, both mammal/vertebrate limbs).
• Homologous or analogous: bird wing & insect wing? → Analogous.
• Fossil evidence uses which method for dating? — Radioactive dating (½-life of C-14, U-Pb, K-Ar).