🧬 Biology

Biology, quick reference

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Key concepts across the three externals, condensed. Remember: always link a response/trend to its survival value.

Tropisms (directional plant growth): photo-, gravi-, thigmo-, hydro-. Auxin → elongation on shaded side.
Nastic (non-directional): thigmonasty (flytrap), nyctinasty (day/night).
Taxis = directional movement; kinesis = non-directional (rate changes).
Innate (instinct, stable environments) vs learned (habituation, imprinting, conditioning; changing environments).
Rhythms: circadian ~24h, tidal ~12.4h, lunar ~29.5d, annual ~1yr. Endogenous clock reset by zeitgebers.

Variation: mutation (new alleles), sexual reproduction (shuffling), gene flow.
Mechanisms: natural selection (directional/stabilising/disruptive), genetic drift (bottleneck, founder), gene flow, mutation.
Isolation: pre-zygotic (temporal, ecological, behavioural, mechanical, gametic) vs post-zygotic (hybrid inviable/sterile).
Speciation: allopatric (geographic) vs sympatric (e.g. polyploidy).
Patterns: divergent, convergent, coevolution; gradualism vs punctuated equilibrium.

Bipedal evidence: central foramen magnum, S-spine, bowl pelvis, valgus (carrying) angle, arched foot, in-line big toe.
Advantages: free hands, see over grass, energy-efficient, thermoregulation.
Cranial trends: ↑ brain size; ↓ brow ridges, prognathism, teeth/jaw; chin appears.
Cultural: tools (Oldowan→Acheulean), fire, language, art: fast, learned, not genetic.