Selection, drift, inbreeding and eugenics

Microevolution is a change in allele and genotype frequencies. Name the force, then a human example.

• Mutation: new alleles, usually rare.
• Natural selection: Darwin’s filter — directional, stabilising, disruptive.
• Disruptive: two extremes favoured, middle punished (rare in humans; squirrel-tail teaching image).
• Gene flow: migration mixes pools.
• Genetic drift: chance in small populations — founder effect (Pingelap retinitis pigmentosa teaching case) and bottleneck.

• Inbreeding raises homozygosity; hidden recessives surface.
• Darwin–Wedgwood cousin marriage is a biographical caution, not a law of nature.
• Royal haemophilia (Queen Victoria, X-linked) is the classic pedigree story — use as X-linkage, not gossip.
• Lethal recessives: sickle-cell and thalassaemia homozygotes. Dominant lethals often late-onset (Huntington teaching case) so reproduction still happens.
• India: endogamy + diversity → inherited-disorder load; UMMID / NIDAN screening is the policy peg. Dor Yeshorim-type carrier screening is the comparative Jewish-community case.
• Gene classes in the teaching notes: super-vital (adaptive edge, e.g. DEC2 short-sleep), vital, sub-vital, lethal, and sterile — a survival ranking of alleles, not a moral ranking of people.
• Genomic imprinting: some genes run only from the mother or only from the father (one parental copy silenced). Prader–Willi / Angelman on 15q is the usual pair: same deletion, different parent, different syndrome.

• Francis Galton named eugenics: improve a ‘stock’ by controlling who reproduces.
• Positive eugenics: encourage the ‘fit’. Negative: restrict, sterilise, murder — US court-backed sterilisation and Nazi racial policy are the warning cases.
• Anthropology’s job is to show how race science and state power fused — not to offer a breeding programme.