The chemical evolution theory (Oparin, 1924; Haldane, 1929) proposes that life originated from simple inorganic molecules through chemical reactions in a primordial reducing atmosphere that lacked free oxygen.

The Miller-Urey experiment (1953) provided experimental support by producing amino acids (glycine, alanine) from CH4, NH3, H2, and H2O under electric discharge, simulating early Earth conditions.

Paleontological evidence (fossil record with transitional forms), comparative anatomy (homologous and analogous organs), and molecular evidence (cytochrome c sequences) together provide multiple independent lines of support for biological evolution.

Homologous organs share the same embryonic origin but perform different functions, indicating divergent evolution from a common ancestor (e.g., forelimbs of whale, bat, horse, human).

Analogous organs have different embryonic origins but perform similar functions, indicating convergent evolution due to similar environmental pressures (e.g., wings of bat and butterfly; eyes of octopus and mammals).

Darwin's theory of natural selection operates through variation, heredity, overproduction, and differential reproduction, and acts in three modes: stabilizing (reduces variation), directional (shifts mean), and disruptive (favours extremes).

The Hardy-Weinberg principle states that allele frequencies remain constant (p + q = 1; $p^{2}$ + 2pq + $q^{2}$ = 1) when five conditions are met — no mutation, migration, selection, drift, or non-random mating — and serves as a mathematical null hypothesis for detecting evolution.

Speciation occurs through allopatric pathways (geographic isolation → divergence → reproductive isolation) or sympatric pathways (polyploidy in plants), and adaptive radiation (Darwin's finches; Australian marsupials) exemplifies rapid diversification into multiple ecological niches from one ancestor.

Human evolution proceeded from Dryopithecus (~15 mya, ape-like) through Ramapithecus, Australopithecus (first biped, ~5 mya), Homo habilis (first tools, ~2 mya), and Homo erectus (first fire, ~1.5 mya) to modern Homo sapiens sapiens (~0.2 mya, 1300-1400 cc brain, language, art).

The two most critical NEET facts are: distinguishing homologous organs (same origin, divergent evolution) from analogous organs (different origin, convergent evolution), and correctly applying the Hardy-Weinberg equation ($q^{2}$ → q → p → 2pq) to calculate allele and genotype frequencies.