Chapter 6 — Evolution

NCERT Class 12 Biology Chapter 6 covers Evolution, explaining the origin of life through chemical evolution, Darwin's theory of natural selection, evidences for evolution, adaptive radiation, the Hardy-Weinberg principle, and the evolutionary history of life forms including the origin and evolution of man.

Evolution, Chapter 6 of NCERT Class 12 Biology, traces the history of life on Earth from the Big Bang (13.8 billion years ago) to the origin of the first cellular life forms around 2000 million years ago. It covers the Oparin-Haldane hypothesis of chemical evolution, Miller's 1953 experiment demonstrating synthesis of amino acids, Darwin's theory of natural selection, and evidences from fossils, comparative anatomy, and biochemistry. Key concepts include adaptive radiation (Darwin's finches, Australian marsupials), the Hardy-Weinberg principle of genetic equilibrium, and the evolutionary timeline from early primates like Dryopithecus and Ramapithecus to modern Homo sapiens.

1. 01The universe is approximately 13.8 billion years old; Earth formed about 4.5 billion years ago, and life first appeared nearly 4 billion years ago.
2. 02Miller's 1953 experiment demonstrated that amino acids can form abiotically by passing electric discharge through CH₄, H₂, NH₃, and water vapour at 800°C, supporting the chemical evolution hypothesis.
3. 03Darwin's theory of natural selection holds that heritable variations conferring better fitness enable individuals to leave more progeny, driving gradual evolution; Alfred Wallace independently reached similar conclusions.
4. 04Homologous structures (e.g., forelimbs of whales, bats, cheetahs, and humans) indicate divergent evolution and common ancestry, while analogous structures (e.g., wings of birds and butterflies) indicate convergent evolution.
5. 05Hardy-Weinberg principle states that allele frequencies in a population remain constant across generations (genetic equilibrium); disturbances caused by gene flow, genetic drift, mutation, recombination, or natural selection result in evolution.
6. 06Homo sapiens arose in Africa; Neanderthal man (brain size ~1400cc) lived 1,00,000–40,000 years ago, and modern Homo sapiens emerged during the ice age between 75,000–10,000 years ago.