Evolutionary Biology → Study of history of life forms on earth
Evolution → Understanding changes in flora and fauna over millions of years on earth
According to Darwin → Descent with modification (Variation)
Unit of Evolution → Population
Raw material of Evolution → Variation
Timeline of Origin
Event
Time
Key Details
Origin of Universe
20 B.Y.A
Big Bang Theory — Huge gaseous cloud → Dust + inert gases → Nebuli/Galaxies → Solar System
Origin of Earth
4.5 B.Y.A
Single Nibuli → Earth formed with Earth Crust (outer) and Core (inner)
Origin of Life
4.0 B.Y.A
500 million years after formation of Earth
Non-Cellular Life
3.0 B.Y.A
Giant molecules — Protein, RNA, Polysaccharide
Cellular Life
2.0 B.Y.A
Unicellular → Multicellular
Primitive Atmosphere of Early Earth
Primitive atmosphere conditions: NH₃ + CH₄ + H₂ + water vapour — Reducing Conditions. O₂ was NOT present in free form in the primitive atmosphere.
💡 Big Bang Theory: Huge gaseous cloud → Temp ↑ then ↓ → Size ↑ → formed Solid entity, Dust + inert gases → Nebuli/Galaxies (with solid entity + temp ↑ inside, temp ↓ outer surface) → Single Nibuli → Solar System → Earth
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Theories to Explain Origin of Life
Section 02
#
Theory
Key Points
1
Theory of Special Creation
Life was created by God/divine power
2
Theory of Catastrophism
Life destroyed and recreated by catastrophes
3
Theory of Panspermia / Cosmozoic Theory
Life came from outside. Early Greek thinkers thought units of life called Spores were transferred to different planets including Earth. Still a favourite idea for some astronomers.
4
Theory of Spontaneous Generation / Abiogenesis (Aristotle & Von Helmont)
Life arises spontaneously out of non-living matter. Von Helmont — within 21 days, rats produced from wheat grains kept with a shirt drenched in sweat.
5
Theory of Biogenesis (Francesco Redi, Spallanzani, Louis Pasteur)
Disproved spontaneous generation. New organisms can only be formed from pre-existing ones. Omnis vivum ex vivo.
6
Oparin-Haldane Theory / Chemical Evolution / Theory of Pri-Abiogenesis
Alexander Oparin (Russian biochemist, wrote book 'Origin of Life'). J.B.S. Haldane (English physiologist who settled in India in Bhubaneswar). Simple molecules → Complex biomolecules in water (Hot Dilute Soup). Life originated in water. Energy sources: Volcanic eruptions, Lightning, UV and X-Rays.
⚗️
Miller's Experiment & Biological Evolution
Section 03
Miller's Experiment
Devoid of radiation (UV rays not present)
Gases used: CH₄ : NH₃ : H₂ = 2 : 1 : 2
Simulated primitive Earth conditions to prove Oparin-Haldane theory
Produced amino acids and other organic molecules — supporting chemical evolution
Biological Evolution — From Protobionts to First Life
💡 This is the Endosymbiotic Theory — mitochondria and chloroplasts were originally free-living prokaryotes that were engulfed by larger cells and established a symbiotic relationship. Evidence: both have circular DNA, double membrane, and reproduce independently.
🦴
Evidences in Favour of Evolution
Section 05
1. Palaeontological Evidences (Fossil Record)
Fossils: Remains or traces of non-degraded parts of ancient living things found within rock life preserved in the Earth Crust. Palaeontology = Study of fossils.
Types of Fossils: (1) Unaltered fossils (e.g. Wooly Mammoth) (2) Petrified fossils — Deposition of inorganic substances (mostly in sedimentary rocks) (3) Mould (4) Cast = Petrified mould (5) Print
Age of Fossils — Radioactive Dating
Radioactive Substance
Half Life
Stable Product
Use
C¹⁴ (Unstable)
5730 ± 40 years or 5760 Y
N¹⁴ (Stable)
Dating recent fossils (up to ~50,000 years)
U²³⁸ (Unstable)
Millions of years
Pb²⁰⁷ (Stable)
Dating very old fossils/rocks
Ratio of RA & NRA Sub: 1st ½ life = 1:1 · 2nd ½ life = 1:3
📌 Electron Spin Resonance (ESR) → Modern and accurate technique for fossil dating.
2. Evidences from Comparative Anatomy — Homologous & Analogous Organs
Type
Structure
Function
Evolution type
Examples
Homologous Organs
Similar fundamental structure
Different functions
Divergent evolution · Common ancestry
Forelimbs of man, cheetah, whale, bat · Mouth parts of cockroach, honey bee, mosquito, butterfly · Thorn & tendrils of Bougainvillea & Cucurbita
Analogous Organs
Different anatomical structure
Similar function
Convergent evolution
Wings of butterfly & birds · Pectoral fins of sharks & flippers of dolphins · Stings of honey bee & scorpion · Eye of octopus & mammals · Sweet potato (root) & potato (stem)
3. Vestigial Organs
Organs present in reduced form, don't perform any function in the body but correspond to fully developed functional organs of related animals.
Vestigial organs in Human Body: Nictitating membrane (Plica Semilunaris) · Auricular muscles of ear · Segmental muscles of abdomen · Vermiform appendix · Coccyx/tail bone · Third molars (wisdom teeth) · Nipples in male
4. Embryological Evidences
Embryological support for evolution was proposed by Heckel based on observation of certain features during embryonic stage common to all vertebrates but absent in adult (e.g. vestigial gill slits behind head). However, this proposal was disapproved on careful study by Karl Ernst Von Baer. He noted that embryos never pass through adult stages of other animals.
Biogenic Law (According to Hackel): Ontogeny (development of embryo) recapitulates Phylogeny.
5. Evidences from Physiology and Biochemistry
Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry. Example: Pepsin → All Vertebrates · Trypsin → All Invertebrates + All Vertebrates
🐦
Adaptive Radiation
Section 06
Adaptive Radiation = Process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats).
Darwin's Finches — Best Example
During his journey in 1831, Darwin went to Galapagos Islands (22 islands) on ship H.M.S. Beagle · Duration: 5 years
Observed amazing diversity of creatures — small black birds called Darwin's Finches (13 types)
All varieties evolved on the island itself from original seed-eating ancestor
Forms with altered beaks arose — enabling them to become insectivorous, fruit-eating, cactus-eating and vegetarian finches
Other Examples
Australian Marsupials and Placental Mammals — When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats) = Convergent Evolution
Placental wolf and Tasmanian wolf (marsupial) — appear similar but evolved independently
🧑🔬
Theories of Biological Evolution
Section 07
1. Lamarck's Theory (Theory of Inheritance of Acquired Characters)
Also called Theory of use and disuse of organs. Book: Philosophic Zoology
Postulates of Lamarck's Theory:
Internal force → ↑ Size of Body
Formation of new organs in result of the need by organism
Development of organs ∝ its use (transferred into offsprings)
All changes acquired by organism during its life are transferred to offsprings via Germplasm (Gametes)
⚠️ Lamarck's theory was discarded by Weisman's Theory of Germplasm — changes in Somatoplasm (Somatic cell) are NOT transferred to offspring; only Germplasm (gametes) transfers hereditary information.
2. Darwinism (Theory of Natural Selection, 1859)
Darwin was influenced by article "An Essay on Principles of Population" by T.R. Malthus. Alfred Wallace (naturalist working in Archipelago/present Indonesia) also came to similar conclusions around the same time.
Main points of Theory of Natural Selection:
High rate of Reproduction
Total number almost constant → Resources are limited
Struggle for existence (Competition):
Intraspecific — between members of same species
Interspecific — between members of different species → Responsible for evolution
Natural Selection → Individual with maximum useful variation selected by Nature
Survival of the Fittest → Fitness is end result of the ability to adapt & get selected by Nature
Two Key Concepts of Darwin's Theory:
Branching Descent
Pattern of Evolution — adaptive and non-adaptive branching pattern
Natural Selection
Mechanism of Evolution — adaptive and non-adaptive selection by Nature
Darwin said appearance of new life forms is due to Accumulation of Variation from one generation to another.
Other theories of Darwin: Theory of Artificial Selection · Theory of Sexual Selection · Theory of Pangenesis (rejected by Weismann's Theory of Germplasm)
🦋
Industrial Melanism & Mutation Theory
Section 08
Industrial Melanism — Peppered Moth (Biston betularia), England
Period
Black Moth
White Moth
Reason
Before Industrialisation (1850)
↓ Fewer
↑ More
White moths camouflaged on lichen-covered white trees
After Industrialisation (1920)
↑ More
↓ Fewer
Trees became black with soot; black moths camouflaged; white moths visible to predators
📌 Industrial Melanism is the most cited example of Natural Selection in action. It proves Darwin's concept of selection — environment selects pre-existing variants, it does NOT create new ones.
3. Mutation Theory (Hugo de Vries)
Hugo de Vries worked on Evening Primrose (Oenethera lamarkiana). According to Mutation Theory:
Mutations are responsible for Evolution
Mutations provide raw material for Evolution
Mutations are source of Discontinuous Variation
Aspect
Darwin
Hugo de Vries
Variation
Small, Continuous, Directional, Adaptive
Large, Discontinuous, Non-Directional, Random
Evolution
Slow and Gradual
Sudden and Jerky process = Saltation (Single Step) = Large Mutation
📊
Modern/Synthetic Theory & Hardy-Weinberg Principle
Section 09
Modern / Synthetic Theory of Evolution
According to this theory, many factors are responsible for formation of new species:
Gene Migration / Gene Flow
Genetic Drift
Mutation
Recombination → Regular Source of Variation
Natural Selection
Gene Flow
Gene Pool = Total collection of all genes and its alleles in a population. Multiple migration between Population I and Population II → Change in Gene Pool → Responsible for Formation of New Species.
Genetic Drift
Random / Nondirectional change of gene frequencies in small population by chance.
Population size may ↑ or ↓ due to: Geographical Isolation, Migration by chance, Natural Calamity
Bottle Neck Effect → Small population → Isolated population → Founder Effect → New Species
Mutation / Genetic Basis of Adaptation — Lederberg's Experiment
Bacterial colony → Many generations → Colony without antibiotic (penicillin — not present) → Replica → Anti-Sensitive Bacteria → New Species. The new environment does NOT induce mutation — it only selects the pre-existing / pre-adaptive mutation that occurred earlier. Over few generations this results in Speciation → Reproductive Isolation.
Hardy-Weinberg Principle
Gene or Allelic frequency in a large population remains constant = 1, if mating occurs at random and in absence of following 5 factors:
Mutation
Genetic Drift
Recombination
Gene Migration
Natural Selection
Hardy-Weinberg Equation
AA = p²
aa = q²
Aa = 2pq
p² + q² + 2pq = 1 or (p+q)² = 1
p + q = 1
⚠️ Any change in allelic frequency (p or q) indicates evolution is occurring. Hardy-Weinberg equilibrium is maintained only in an idealized, large, randomly mating population with no evolution. In real populations, all 5 factors operate and evolution always occurs.
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MCQ Practice — Evolution
Section 10
Q1. In Miller's experiment, the ratio of CH₄ : NH₃ : H₂ used was:
Miller used CH₄ : NH₃ : H₂ in ratio 2:1:2 to simulate the primitive atmosphere. The experiment was devoid of UV radiation and produced amino acids, proving that organic molecules could be formed under early Earth conditions.
Q2. Forelimbs of man, cheetah, whale and bat are examples of:
Homologous organs have similar fundamental structure but different functions — they are evidence of divergent evolution and common ancestry. Forelimbs of man (grasping), cheetah (running), whale (swimming) and bat (flying) all have same bone structure (humerus, radius, ulna, carpals, metacarpals, phalanges) but very different functions.
Q3. Industrial Melanism in Peppered Moth is an example of:
Industrial Melanism in Peppered Moth (Biston betularia) is the most classic example of Natural Selection. After industrialization, black moths were selected by nature because they were camouflaged on soot-covered trees. This proved that environment selects pre-existing variants, it doesn't create new ones.
Q4. Darwin's Finches in Galapagos Islands are the best example of:
Darwin's Finches (13 types in 22 islands) are the best example of Adaptive Radiation — evolution of different species from a single ancestor in a geographical area, radiating to different habitats. All evolved from original seed-eating ancestor and developed different beak types for different food sources.
Q5. Which of the following was discarded by Weisman's Theory of Germplasm?
Lamarck's Theory (Theory of Inheritance of Acquired Characters) was discarded by Weisman's Theory of Germplasm. Weisman showed that only Germplasm (gametes) is transferred to offspring — Somatoplasm (somatic cell) changes are NOT inherited. This disproved Lamarck's idea that acquired characters during life can be passed to offspring.
Q6. Hardy-Weinberg equilibrium is maintained when:
Hardy-Weinberg principle states that gene/allele frequency remains constant = 1 in a large population, if mating occurs at random AND in absence of: (1) Mutation (2) Genetic Drift (3) Recombination (4) Gene Migration (5) Natural Selection. The equation: p² + q² + 2pq = 1 and p + q = 1.
❓ Frequently Asked Questions
Miller used CH₄ (Methane), NH₃ (Ammonia) and H₂ (Hydrogen) in ratio 2:1:2. The experiment was devoid of UV radiation. This simulated primitive Earth atmosphere conditions and produced amino acids, supporting Oparin-Haldane's Chemical Evolution theory.
Gene or allelic frequency in a large population remains constant = 1, if mating occurs at random and in absence of 5 factors: Mutation, Genetic Drift, Recombination, Gene Migration, and Natural Selection. Equation: p² + q² + 2pq = 1 where p = frequency of dominant allele, q = frequency of recessive allele, p+q = 1.
Homologous: Same structure, different function, divergent evolution, common ancestry (e.g. forelimbs of man, whale, bat, cheetah). Analogous: Different structure, same function, convergent evolution (e.g. wings of butterfly & birds, eye of octopus & mammals, stings of bee & scorpion).
Industrial Melanism in Peppered Moth (Biston betularia) in England: Before industrialization (1850) — black moths fewer, white moths more. After industrialization (1920) — black moths increased, white moths decreased. Trees turned black with soot; black moths became camouflaged, white moths visible to predators. Direct evidence of Natural Selection.
Adaptive Radiation is evolution of different species in a geographical area starting from one point and radiating to other habitats. Best example: Darwin's Finches in Galapagos Islands (22 islands, 13 types of finches from original seed-eating ancestor). Another example: Australian marsupials and placental mammals (Convergent Evolution).
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