Evolution
Class 12 · Biology
4 ideas in Class 12 Biology, explained in plain words, with games and quizzes to practise.
Origin of Life
Part of: Beginnings
The universe began 13.8 billion years back, earth formed 4.5 billion back, and life appeared about 4 billion back. Pasteur ended spontaneous generation, Oparin and Haldane proposed chemical evolution, Miller made amino acids in a flask, and the first cells arose in water about 2000 million years ago.
Why it matters. Timeline order plus experiment conclusions start evolution answers.
Formulas
- Universe 13.8 billion years, earth 4.5 billion
- Life appeared about 4 billion years back
- First cells arose about 2000 million years ago
Key words
- Big Bang
- : The explosion starting the universe.
- Panspermia
- : Life arriving from outer space.
- Spontaneous generation
- : Life from rotting matter, disproved.
- Chemical evolution
- : Molecules forming from inorganic matter.
- Biogenesis
- : Life arising from non-living molecules.
Try it in two minutes
- Order universe, earth and life dates.
- Match each scientist to one result.
- Place first cells in water.
Try at home. Explain why Miller left oxygen out of his flask.
Proof of Change
Part of: Beginnings
Fossils order life through rock layers, embryos share gill slits, homologous limbs show common ancestry while analogous wings show convergent function, and moths plus resistant microbes prove selection within human lifetimes. Breeding shows how fast forms can shift.
Why it matters. Evidence sorting plus moth-logic questions repeat yearly.
Key words
- Fossil
- : Hard remains marking time spans.
- Homologous
- : Same build, different function.
- Analogous
- : Same function, different build.
- Divergent evolution
- : One build radiating to uses.
- Convergent evolution
- : Builds converging on one use.
- Anthropogenic evolution
- : Change driven by human action.
Try it in two minutes
- Split homologous from analogous pairs.
- Flip moth colours with soot.
- Clock resistance in months.
Try at home. Explain why rural moth counts stayed light-winged.
Theories and Hardy-Weinberg
Part of: How Evolution Works
Lamarck trusted use and disuse, Darwin proved selection for reproductive fitness, and de Vries proposed sudden saltation. Hardy-Weinberg holds p squared plus 2pq plus q squared at 1 until migration, drift, mutation, recombination or selection disturb it. Founder drift can start new species.
Why it matters. Frequency arithmetic plus theory contrast is the numerical heart of the chapter.
Formulas
- p squared plus 2pq plus q squared equals 1
- Allele frequencies sum to 1
Key words
- Natural selection
- : Fitter variants leaving more progeny.
- Fitness
- : Reproductive success in an environment.
- Saltation
- : Single-step large mutation.
- Gene pool
- : All alleles in a population.
- Genetic drift
- : Chance shifts in allele frequency.
- Founder effect
- : Drift starting new species.
Try it in two minutes
- Place three thinkers on a timeline.
- Square p and q into genotypes.
- Name all five disturbers.
Try at home. Explain why giraffe necks refute Lamarck.
History of Life and Humans
Part of: Story of Life
Invertebrates rose by 500 million years ago, jawless fish by 350, land plants by 320, and dinosaurs exited 65 million back. Mammals then spread; Dryopithecus and Ramapithecus came 15 million back, walkers by 3 to 4, Australopithecines by 2, erectus with 900cc by 1.5, Neanderthals with 1400cc, then modern humans with art at 18000 and farming at 10000 years back.
Why it matters. Date order plus brain-size trends answer match-the-stage questions.
Formulas
- Dinosaurs exited 65 million years back
- Habilis 650 to 800cc, erectus 900cc, Neanderthal 1400cc
- Cave art 18000 years back, farming 10000 years back
Key words
- Australopithecines
- : Early walkers hunting with stones.
- Homo habilis
- : First human-like tool users.
- Homo erectus
- : Upright users of larger brains.
- Neanderthal
- : Stocky burials with big brains.
- Homo sapiens
- : Modern humans farming and painting.
Try it in two minutes
- Chain five geological dates.
- Chain five human stages.
- Grow brains 700 to 900 to 1400.
Try at home. Explain why Australian pouched mammals survived.
What your child will practise
- History of Life and Humans: Jungle Puzzle (Clue Puzzle)
- History of Life and Humans: Jungle Quick Fire (Quick Fire)
- Origin of Life: Candy Puzzle (Clue Puzzle)
- Proof of Change: Candy Quest (Flip and Match)
- Theories and Hardy-Weinberg: Space Quick Fire (Quick Fire)
- Quiz: History of Life and Humans (8 questions)
- Quiz: Origin of Life (8 questions)
- Quiz: Proof of Change (8 questions)
- Quiz: Theories and Hardy-Weinberg (8 questions)