Class 12 Biology: Quick Revision Notes

Chapter: Evolution (विकास)

Universe Age: Approximately 20 billion years old.
Earth Formation: Formed about 4.5 billion years back. Life appeared 500 million years after formation (approx. 4 billion years ago).
Panspermia: Units of life called spores transferred to different planets including Earth (early Greek concept).
Spontaneous Generation: The theory that life came out of decaying and rotting matter like straw, mud, etc. (Discarded by Louis Pasteur).
Biogenesis: Life originates from pre-existing life. (Demonstrated by Louis Pasteur using swan-necked flasks).
Oparin-Haldane Theory: Life originated from pre-existing non-living organic molecules (e.g., RNA, protein, etc.) and that formation of life was preceded by chemical evolution.

Homologous Organs (समजात अंग):
- Same structure and embryonic origin, but perform different functions.
- Indicates Divergent Evolution (अपसारी विकास).
- Example: Forelimbs of humans, cheetah, whale, and bat.
Analogous Organs (समवृत्ति अंग):
- Different structures and origin, but perform similar functions due to similar habitat.
- Indicates Convergent Evolution (अभिसारी विकास).
- Example: Wings of butterfly and birds, eyes of octopus and mammals.
Vestigial Organs (अवशेषी अंग): Non-functional organs in humans that were functional in ancestors (e.g., Vermiform appendix, nictitating membrane, wisdom teeth).
Embryological Evidences: Ernst Haeckel proposed "Ontogeny recapitulates phylogeny" (Embryos of all vertebrates share common structural features during development).

Lamarckism (Theory of Inheritance of Acquired Characters):
- Proposed by Jean-Baptiste Lamarck.
- States that use and disuse of organs and acquired characters are inherited by the next generation (e.g., Long neck of giraffes).
Darwinism (Theory of Natural Selection):
- Proposed by Charles Darwin (based on observations during voyage in H.M.S. Beagle).
- Two key concepts:
  1. Branching Descent
  2. Natural Selection (प्राकृतिक चयन): Organisms with better adaptability survive and reproduce (Survival of the fittest).
Hugo de Vries (Mutation Theory):
- Mutations are sudden, large, and directionless changes (saltation) responsible for evolution, unlike Darwin's small, gradual variations.

States that allele frequencies in a population are stable and remain constant from generation to generation (Genetic Equilibrium / जीन साम्यावस्था).
Mathematical Equation: (p + q)^2 = p^2 + 2pq + q^2 = 1
- Where:
  - p = Frequency of allele A
  - q = Frequency of allele a
  - p^2 = Frequency of homozygous dominant individuals (AA)
  - q^2 = Frequency of homozygous recessive individuals (aa)
  - 2pq = Frequency of heterozygous individuals (Aa)
Factors affecting Hardy-Weinberg Equilibrium:
1. Gene migration or gene flow (जीन प्रवाह)
2. Genetic drift (आनुवंशिक विचलन)
3. Mutation (उत्परिवर्तन)
4. Genetic recombination (आनुवंशिक पुनرकॉम्बिनेशन)
5. Natural selection (प्राकृतिक चयन)

Dryopithecus & Ramapithecus: Apes that existed 15 million years ago. Ramapithecus was more man-like, Dryopithecus more ape-like.
Australopithecines: Lived in East African grasslands 2 million years ago. Hunted with stone weapons, ate fruit.
Homo habilis: First human-like hominid (Handyman). Brain capacity: 650-800 cc.
Homo erectus: Existed 1.5 million years ago. Ate meat. Brain capacity: 900 cc.
Neanderthal Man: Lived in near east and central Asia between 1,00,000 to 40,000 years back. Used hides to protect body and buried their dead. Brain capacity: 1400 cc.
Homo sapiens (Modern Man): Arose in Africa between 75,000-10,000 years ago (Ice Age). Developed art and agriculture.

Adaptive Radiation (अनुकूलित विकिरण): Evolution of different species in a given geographical area starting from a point and radiating to other areas (e.g., Darwin’s Finches, Australian marsupials).
Saltation: Single-step large mutation.
Atavism: Reversion of some ancestral characters (e.g., tail in human baby).