Evolution (NEET Biology)

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### Origin of Life - **Big Bang Theory:** Explains origin of universe. Universe formed ~20 billion years ago. - **Early Earth:** Formed ~4.5 billion years ago. No atmosphere, high temperature, UV rays, volcanic storms, reducing atmosphere (CH$_4$, NH$_3$, H$_2$O, H$_2$). - **Oparin-Haldane Theory (Chemical Evolution):** Life originated from pre-existing non-living organic molecules (RNA, protein, etc.). First life form was chemoheterotroph. - **Miller's Experiment (1953):** S.L. Miller and H.C. Urey demonstrated chemical evolution. - **Apparatus:** Electric discharge in a closed flask containing CH$_4$, H$_2$, NH$_3$, and water vapor at 800°C. - **Result:** Formation of amino acids, sugars, nitrogen bases, pigments, fats. - **First Cellular Form:** Arose ~3 billion years ago. Non-cellular aggregates (coacervates, microspheres). - **Biogenesis:** Life comes only from pre-existing life. Louis Pasteur disproved spontaneous generation. ### Theories of Evolution #### Lamarckism (Theory of Inheritance of Acquired Characters) - Proposed by Jean Baptiste Lamarck. - **Postulates:** 1. **Use and Disuse of Organs:** Organs used more develop more; unused organs degenerate. 2. **Inheritance of Acquired Characters:** Characters acquired during an organism's lifetime are inherited by offspring. - **Example:** Giraffe's long neck (stretching to eat leaves), loss of limbs in snakes. - **Disproved by:** August Weismann (cut tails of mice for 21 generations, offspring still had tails). #### Darwinism (Theory of Natural Selection) - Proposed by Charles Darwin. Based on observations during voyage of H.M.S. Beagle. - **Key Concepts:** 1. **Overproduction/Prodigality of Production:** Organisms produce more offspring than can survive. 2. **Struggle for Existence:** Competition for food, space, mate. (Intraspecific, Interspecific, Environmental). 3. **Variation:** Individuals within a population show variations (raw material for evolution). 4. **Survival of the Fittest (Natural Selection):** Individuals with favorable variations are better adapted and survive to reproduce. 5. **Inheritance of Useful Variations:** Favorable variations are passed on to offspring. 6. **Origin of New Species:** Accumulation of variations over generations leads to speciation. - **Alfred Wallace:** Co-proposed similar ideas. Papers presented jointly in 1858. - **Criticism:** Did not explain origin of variations, inheritance mechanism. #### Hugo de Vries - Mutation Theory - Observed *Oenothera lamarckiana* (Evening Primrose). - **Mutations:** Sudden, heritable, discontinuous variations. - **Key Points:** - Mutations are random and directionless. - Mutations cause evolution (saltation - single step large mutation). - Darwinian variations are small and directional. ### Evidences for Evolution #### 1. Paleontological Evidence - **Fossils:** Petrified remains of life forms found in sedimentary rocks. - **Study of Fossils:** Paleontology. - **Significance:** Show past life forms, evolutionary pathways (e.g., horse evolution). - **Connecting Links:** *Archaeopteryx* (reptiles and birds). #### 2. Comparative Anatomy and Morphology - **Homologous Organs:** Same basic structural plan, different functions. Indicate **divergent evolution** (common ancestry). - **Examples:** Forelimbs of whale, bat, cheetah, human; Vertebrate hearts/brains; Thorn of Bougainvillea & Tendril of Cucurbita. - **Analogous Organs:** Different basic structural plan, similar functions. Indicate **convergent evolution** (different ancestry, similar habitat). - **Examples:** Wings of insects & birds; Eye of octopus & mammals; Flippers of penguins & dolphins; Sweet potato (root modification) & Potato (stem modification). #### 3. Embryological Evidence - **Recapitulation Theory (Biogenetic Law):** "Ontogeny repeats Phylogeny" proposed by Ernst Haeckel. - Embryos pass through stages resembling adult forms of their ancestors. - **Example:** Vertebrate embryos all develop a rudimentary gill slit stage (even though not all adults have gills). - **Disproved by:** Karl Ernst von Baer (embryos never pass through adult stages of other animals). #### 4. Molecular Evidence - Similarities in proteins, DNA, biochemical processes among diverse organisms. - **Example:** Cytochrome c sequence similarity (further species are, more differences). #### 5. Adaptive Radiation - Evolution of different species from a common ancestor in a given geographical area, adapting to different ecological niches. - **Examples:** - **Darwin's Finches:** On Galapagos Islands, various beak types evolved from original seed-eating finches. - **Australian Marsupials:** A variety of marsupials (e.g., Koala, Wombat, Bandicoot) evolved from a common ancestral marsupial. #### 6. Industrial Melanism - **Example:** *Biston betularia* (peppered moth) in England. - **Pre-industrial era:** White-winged moths (camouflaged on lichen-covered trees) were dominant. - **Post-industrial era:** Soot-covered trees killed lichens; dark-winged moths camouflaged better, increased in population. - **Conclusion:** Natural selection in action. #### Comparison Table: Homologous vs Analogous Organs | Feature | Homologous Organs | Analogous Organs | | :---------------- | :------------------------------------------------- | :------------------------------------------------ | | **Origin/Structure** | Similar anatomical structure, different functions. | Different anatomical structure, similar functions. | | **Ancestry** | Common ancestry | Different ancestry | | **Evolution** | Divergent evolution | Convergent evolution | | **Result** | Adaptive radiation | Parallel evolution | #### Comparison Table: Adaptive Radiation vs Convergent Evolution | Feature | Adaptive Radiation | Convergent Evolution | | :------------------ | :----------------------------------------------------------- | :----------------------------------------------------------- | | **Ancestry** | Common ancestor | Different ancestors | | **Environment** | Species diverge to adapt to different niches in one area. | Unrelated species evolve similar features due to similar environmental pressures. | | **Homology/Analogy** | Leads to homologous structures. | Leads to analogous structures. | | **Example** | Darwin's finches, Australian marsupials | Wings of bird and insect, Eye of octopus and mammal | ### Hardy-Weinberg Principle - **Principle:** Allele frequencies in a population are stable and constant from generation to generation in the absence of evolutionary influences. - **Equation:** $p^2 + 2pq + q^2 = 1$ - $p^2$ = frequency of homozygous dominant individuals (AA) - $q^2$ = frequency of homozygous recessive individuals (aa) - $2pq$ = frequency of heterozygous individuals (Aa) - $p$ = frequency of allele A - $q$ = frequency of allele a - $p + q = 1$ - **Assumptions (Conditions for equilibrium):** 1. Large population size (no genetic drift). 2. Random mating. 3. No mutation. 4. No gene flow (migration). 5. No natural selection. - **Factors Affecting Hardy-Weinberg Equilibrium (Causes of evolution):** 1. **Gene Migration/Gene Flow:** Movement of alleles between populations. 2. **Genetic Drift:** Random change in allele frequencies due to chance events, especially in small populations. - **Founder Effect:** A small group separates from a larger population to form a new population; the new population's gene pool may not be representative of the original. - **Bottleneck Effect:** A drastic reduction in population size due to a disaster, resulting in altered allele frequencies. 3. **Mutation:** Sudden, heritable changes in genetic material. 4. **Genetic Recombination:** New combinations of alleles during sexual reproduction. 5. **Natural Selection:** Differential reproduction of individuals based on fitness. #### Natural Selection Types - **Stabilizing Selection:** Favors intermediate phenotypes, eliminates extreme ones. (e.g., Human birth weight). - **Directional Selection:** Favors one extreme phenotype. (e.g., Industrial melanism, antibiotic resistance). - **Disruptive Selection:** Favors both extreme phenotypes, selects against intermediate ones. (e.g., Beak size in African finches). ### Speciation - **Definition:** The process by which new species arise from pre-existing ones. - **Reproductive Isolation:** Key factor preventing interbreeding between different species. - **Pre-zygotic barriers:** Habitat, temporal, behavioral, mechanical, gametic isolation. - **Post-zygotic barriers:** Hybrid inviability, hybrid sterility, hybrid breakdown. ### Origin and Evolution of Man - **Ancestors:** Tree shrews, Tarsiers, Monkeys, Apes. - **Key Evolutionary Trends:** Bipedalism, increase in brain size, decrease in prognathism, tool use, cultural development. #### Flowchart: Human Evolution ```mermaid graph TD A[Dryopithecus & Ramapithecus] --> B{~15 Mya}; B --> C[Australopithecines]; C --> D{~2 Mya, East African grasslands}; D --> E[Homo habilis]; E --> F{Brain capacity 650-800 cc, ate meat}; F --> G[Homo erectus]; G --> H{~1.5 Mya, Brain capacity 900 cc, ate meat, used fire}; H --> I[Neanderthal man]; I --> J{1,400 cc brain, lived in caves, buried dead, ~100,000-40,000 years ago}; J --> K[Homo sapiens]; K --> L{~75,000-10,000 years ago, Cro-Magnon man, 1350 cc brain, cave art}; L --> M[Modern Homo sapiens]; M --> N{~10,000 years ago, agriculture, settlements}; ``` - **Dryopithecus:** Ape-like, hairy, walked like gorillas and chimpanzees. - **Ramapithecus:** Man-like, more erect posture. - **Australopithecines:** - Lived in East African grasslands ~2 Mya. - Walked upright, ate fruit. - Brain capacity ~400-500 cc. - **Homo habilis:** - "Handy man," first to make tools. - Brain capacity 650-800 cc. - Probably did not eat meat. - **Homo erectus:** - ~1.5 Mya. - Brain capacity ~900 cc. - Ate meat, used fire. - **Neanderthal man:** - Lived in East and Central Asia ~100,000-40,000 years ago. - Brain capacity ~1400 cc. - Used hides to protect body, buried their dead. - **Homo sapiens (Cro-Magnon man):** - Arose in Africa ~75,000-10,000 years ago. - Brain capacity ~1350 cc. - Developed cave art. - **Modern *Homo sapiens*:** Arose ~10,000 years ago. ### Important NEET Revision Points 1. **Miller's experiment:** Created amino acids, not living cells. Conditions were reducing. 2. **Homology = Divergent Evolution = Common Ancestry.** 3. **Analogy = Convergent Evolution = Different Ancestry.** 4. **Industrial Melanism:** Example of natural selection, not mutation. 5. **Hardy-Weinberg equilibrium:** Only holds if no evolution is occurring. 6. **Genetic drift:** More significant in smaller populations. 7. **Natural selection:** Acts on existing variations, does not create them. 8. **Saltation:** Single step large mutation (De Vries). 9. **Australopithecus:** First hominid to walk upright. 10. **Neanderthal man:** First to bury their dead.