Evolution Class 12 Notes PDF Download | NEET 2027 Biology Chapter 6 NCERT

*EVOLUTION CHAPTER 6 - FULL SHORT NOTES* 📚 *NEW NCERT*  

*NEET 2027 

### *6.1 ORIGIN OF LIFE*

1. *Big Bang*: Universe 20 billion years ago

2. *Early Earth*: No atmosphere → Water vapor, CH₄, CO₂, NH₃ 

3. *Miller-Urey Exp 1953*: CH₄ + NH₃ + H₂ + H₂O + Electric spark → *Amino acids* bane = *Chemical evolution ka first proof*

### *6.2 EVOLUTION OF LIFE FORMS - THEORY*

1.*Darwin.   *Branching descent + Natural Selection* = _On the Origin of Species_ 1859

2. *Natural Selection* = Overproduction + Struggle for existence → *Survival of the fittest* - Herbert Spencer ka term

### *6.3 EVIDENCES FOR EVOLUTION*

**Evidence** **Example** **Type**

**Homologous organs** Human hand, Whale flipper, Bat wing **Divergent evolution**

**Analogous organs** Bird wing vs Insect wing **Convergent evolution**

**Fossils** **Archaeopteryx** = Reptile + Bird Missing link

### *6.4 ADAPTIVE RADIATION* = Ek ancestor → Alag-alag area → Nayi species

1. *Darwin Finches*: Seed eater, Insect eater, Cactus eater beaks

2. *Australian Marsupials*: Kangaroo, Koala, Wombat = Marsupial radiation

3. *Placental mammals* bhi Australia me same tarah evolve hue = *Convergent evolution*

### *6.5 BIOLOGICAL EVOLUTION* 

= Populations me allele frequency ka change hona. *Natural selection hi mechanism hai*.

### *6.6 MECHANISM OF EVOLUTION*

*Natural Selection ke 3 Types*:

1. *Stabilizing*: Middle select → *Human birth weight* 3-3.5 kg

2. *Directional*: Ek extreme select → *DDT resistance*, Peppered moth

3. *Disruptive*: Dono extreme select → *Finches - badi vs choti chonch*

### *6.7 HARDY-WEINBERG PRINCIPLE*

*Equation*: $p^2 + 2pq + q^2 = 1$ ; $p + q = 1$  

*5 Factors jo H-W todte hain "GMG SND"*: *G*ene flow, *M*utation, *G*enetic drift, *S*election, *N*on-random mating  

*Genetic Drift* = *Founder effect* + *Bottleneck effect*  

*NEET Trick*: q² = aa % → root karo = q → p = 1-q → 2pq = Heterozygous %

### *6.8 A BRIEF ACCOUNT OF EVOLUTION*

1. *First cells*: 2000 million years ago

2. *Jawless fish*: 350 mya

3. *Fish → Amphibia*: 320 mya, *Lobefins* = Amphibia ke ancestor

4. *Reptiles*: 200 mya, *Dinosaurs extinct* 65 mya

5. *First mammals*: 200 mya, *South America mammals* extinct due to continental drift

### *6.9 ORIGIN & EVOLUTION OF MAN*

**Stage** **Brain Capacity** **Imp Point**

**Dryopithecus** - Ape-like

**Ramapithecus** - Man-like

**Australopithecus** **500 cc** Hunted with stone

**Homo habilis** **650-800 cc** **First tool maker**

**Homo erectus** **900 cc** **Used fire**

**Neanderthal** **1400 cc** **Largest brain**, East-West Asia, Buried dead

**Homo sapiens** **1350 cc** Cave art, Agriculture 10k years ago

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*NEET 2027 REVISION CHECKLIST* ✅

1. *Miller-Urey gases*: CH₄, NH₃, H₂, H₂O

2. *H-W Numerical*: 4% diseased aa → Heterozygous = 32%

3. *Directional selection ex*: DDT, Industrial melanism

4. *Brain capacity order*: 500 → 650-800 → 900 → 1400 → 1350 cc

5. *Archaeopteryx* = Missing link