Evolution

Key Concepts

Origin of Life

Evolutionary Biology is the study of the history of life forms on earth.

The Big Bang Theory: Explains the origin of the universe (~13.8 billion years ago). Earth formed ~4.5 billion years ago.
Early Earth Conditions: High temperature, reducing atmosphere (CH4, NH3, H2O vapour, CO2), no ozone layer.
Theories on Origin of Life:
- Panspermia: Units of life (spores) came from outerspace.
- Spontaneous Generation: Life arose from decaying matter (dismissed by Louis Pasteur).
- Chemical Evolution (Oparin and Haldane): First form of life arose from non-living organic molecules.
Miller’s Experiment (1953): S.L. Miller created similar conditions (electric discharge, 800°C) and observed the formation of amino acids, supporting chemical evolution.

Evolution of Life Forms - A Theory

Theory of Special Creation: Conventional religious belief (dismissed by scientific evidence).
Charles Darwin: Based on his voyage on H.M.S. Beagle, he concluded that existing life forms share similarities and common ancestors.
Natural Selection: Individuals with better adaptive characteristics (reproductive fitness) leave more progeny and are selected by nature.
Alfred Wallace: A naturalist who reached similar conclusions independently.

Evidences for Evolution

Paleontological Evidence: Study of fossils (remains of life forms in sedimentary rocks).
Comparative Anatomy and Morphology:
- Homologous Organs: Same structure, different functions (e.g., forelimbs of humans, cheetahs, bats, and whales). Indicates divergent evolution and common ancestry.
- Analogous Organs: Different structure, same function (e.g., wings of butterfly and birds, eye of octopus and mammals). Indicates convergent evolution.

Divergent vs Convergent Evolution Homology indicates common ancestry (divergent evolution), while Analogy indicates similar adaptations to a common environment (convergent evolution).

Biochemical Evidence: Similarities in proteins and genes among diverse organisms.
Anthropogenic Action: Selection of resistant varieties due to herbicides, pesticides, or antibiotics.

Adaptive Radiation

The process of evolution of different species in a given geographical area starting from a point and radiating to other areas (habitats).

Darwin’s Finches: Varieties of birds in Galapagos Islands with different beaks adapted to different food sources.
Australian Marsupials: Diversity of marsupials evolving from a single ancestral stock in Australia.

Mechanism of Evolution

Lamarckism: Theory of use and disuse of organs (e.g., Giraffe's neck). Mostly dismissed.
Mutation Theory (Hugo de Vries): Believed that mutation (large, sudden change) is the cause of evolution. Coined the term saltation (single step large mutation).

Saltation Hugo de Vries proposed that evolution occurs through large, sudden mutations (saltation), unlike Darwin’s theory of gradual variations.

Darwinian Variation: Small and directional; evolution is gradual.

Hardy-Weinberg Principle

States that allele frequencies in a population are stable and constant from generation to generation (Genetic Equilibrium).

Equation: p² + 2pq + q² = 1.

Hardy-Weinberg Equilibrium The principle states that allele frequencies remain constant in the absence of evolutionary influences like mutation, selection, or genetic drift.

Factors affecting equilibrium: Gene migration, Genetic drift, Mutation, Genetic recombination, and Natural Selection.
Founder Effect: When a small group drifts from a population and becomes the founders of a new species.

A Brief Account of Evolution

First cellular life: ~2000 mya.
Invertebrates: ~500 mya.
Jawless fish: ~350 mya.
Dinosaurs: Dominated for 200 million years, disappeared ~65 mya.
First mammals: Like shrews.

Origin and Evolution of Man

Dryopithecus & Ramapithecus: ~15 mya (ape-like and man-like).
Australopithecines: ~2 mya (walked upright, used stone weapons).
Homo habilis: First hominid (650-800cc brain, did not eat meat).
Homo erectus: ~1.5 mya (900cc brain, ate meat).
Neanderthal Man: 1,00,000-40,000 years ago (1400cc brain, buried dead).
Homo sapiens: Arose in Africa ~75,000-10,000 years ago (modern man).

Key Concepts

Evolutionary Biology is the study of the history of life forms on earth.

The Big Bang Theory: Explains the origin of the universe (~13.8 billion years ago). Earth formed ~4.5 billion years ago.

Early Earth Conditions: High temperature, reducing atmosphere (CH4, NH3, H2O vapour, CO2), no ozone layer.

Theories on Origin of Life:

Panspermia: Units of life (spores) came from outerspace.
Spontaneous Generation: Life arose from decaying matter (dismissed by Louis Pasteur).
Chemical Evolution (Oparin and Haldane): First form of life arose from non-living organic molecules.

Miller’s Experiment (1953): S.L. Miller created similar conditions (electric discharge, 800°C) and observed the formation of amino acids, supporting chemical evolution.

Theory of Special Creation: Conventional religious belief (dismissed by scientific evidence).

Charles Darwin: Based on his voyage on H.M.S. Beagle, he concluded that existing life forms share similarities and common ancestors.

Natural Selection: Individuals with better adaptive characteristics (reproductive fitness) leave more progeny and are selected by nature.

Alfred Wallace: A naturalist who reached similar conclusions independently.

Paleontological Evidence: Study of fossils (remains of life forms in sedimentary rocks).

Comparative Anatomy and Morphology:

Homologous Organs: Same structure, different functions (e.g., forelimbs of humans, cheetahs, bats, and whales). Indicates divergent evolution and common ancestry.
Analogous Organs: Different structure, same function (e.g., wings of butterfly and birds, eye of octopus and mammals). Indicates convergent evolution.

Divergent vs Convergent Evolution Homology indicates common ancestry (divergent evolution), while Analogy indicates similar adaptations to a common environment (convergent evolution).

Biochemical Evidence: Similarities in proteins and genes among diverse organisms.

Anthropogenic Action: Selection of resistant varieties due to herbicides, pesticides, or antibiotics.

The process of evolution of different species in a given geographical area starting from a point and radiating to other areas (habitats).

Darwin’s Finches: Varieties of birds in Galapagos Islands with different beaks adapted to different food sources.

Australian Marsupials: Diversity of marsupials evolving from a single ancestral stock in Australia.

Lamarckism: Theory of use and disuse of organs (e.g., Giraffe's neck). Mostly dismissed.

Mutation Theory (Hugo de Vries): Believed that mutation (large, sudden change) is the cause of evolution. Coined the term saltation (single step large mutation).

Saltation Hugo de Vries proposed that evolution occurs through large, sudden mutations (saltation), unlike Darwin’s theory of gradual variations.

Darwinian Variation: Small and directional; evolution is gradual.

States that allele frequencies in a population are stable and constant from generation to generation (Genetic Equilibrium).

Equation: p² + 2pq + q² = 1.

Hardy-Weinberg Equilibrium The principle states that allele frequencies remain constant in the absence of evolutionary influences like mutation, selection, or genetic drift.

Factors affecting equilibrium: Gene migration, Genetic drift, Mutation, Genetic recombination, and Natural Selection.

Founder Effect: When a small group drifts from a population and becomes the founders of a new species.

First cellular life: ~2000 mya.

Invertebrates: ~500 mya.

Jawless fish: ~350 mya.

Dinosaurs: Dominated for 200 million years, disappeared ~65 mya.

First mammals: Like shrews.

Dryopithecus & Ramapithecus: ~15 mya (ape-like and man-like).

Australopithecines: ~2 mya (walked upright, used stone weapons).

Homo habilis: First hominid (650-800cc brain, did not eat meat).

Homo erectus: ~1.5 mya (900cc brain, ate meat).

Neanderthal Man: 1,00,000-40,000 years ago (1400cc brain, buried dead).

Homo sapiens: Arose in Africa ~75,000-10,000 years ago (modern man).

Evolution

Evolution

Key Concepts

Origin of Life

Evolution of Life Forms - A Theory

Evidences for Evolution

Adaptive Radiation

Mechanism of Evolution

Hardy-Weinberg Principle

A Brief Account of Evolution

Origin and Evolution of Man

On this page

Evolution

Evolution

Key Concepts

Origin of Life

Evolution of Life Forms - A Theory

Evidences for Evolution

Adaptive Radiation

Mechanism of Evolution

Hardy-Weinberg Principle

A Brief Account of Evolution

Origin and Evolution of Man

On this page