Evolution – Class 12 Biology Notes | CBSE NCERT Based
🧬 Chapter 7: Evolution – Class 12 Biology Notes 🔹 Introduction Evolution refers to the gradual changes occurring in living organisms over millions of years. It explains the origin of new species from pre-existing ones through various mechanisms like mutation, natural selection, genetic drift, etc. --- 🔹 Origin of Life Big Bang Theory: Universe originated about 20 billion years ago. Early Earth: Formed around 4.5 billion years ago; no oxygen, only methane, ammonia, hydrogen, water vapor. Chemical Evolution: Life began from non-living molecules (Oparin-Haldane theory). Miller-Urey Experiment: Simulated early Earth conditions and created organic molecules (amino acids). 📌 Important Diagram: Miller and Urey's Experiment Setup --- 🔹 Theories of Evolution 1. Lamarckism: Proposed by Jean Baptiste Lamarck. Theory of Inheritance of Acquired Characters. Example: Giraffe's long neck. 2. Darwinism (Natural Selection): Proposed by Charles Darwin. Survival of the fittest. Based on: Var...