Thorough summary of the chapter. Useful for examinations.

1. ORIGIN
&
EVOLUTION OF LIFE
PROF: JAY D. THORVE

2. Origin Of Life (Protobiogenesis)
Theories of Origin of Life:
Special Creation Theory: Oldest theory, based on religious belief, posits that living organisms were
created by a supernatural power.
Cosmozoic Theory (Panspermia): Suggests life may have come to Earth from other planets in the
form of spores or micro-organisms. NASA found potential evidence on Martian rocks.
Spontaneous Generation Theory (Abiogenesis): Proposed life could originate from non-living
material spontaneously but was disproved by Louis Pasteur’s experiments.
Biogenesis Theory: States that living organisms always come from pre-existing living forms through
reproduction

3. Theory of special
creation
Abiogenesis
Biogenesis
Panspermia

4. Chemical Evolution of Life
1. Origin of Earth and Primitive Atmosphere: Earth formed about 4.6
billion years ago from a rotating cloud of hot gases and cosmic dust,
creating the primitive atmosphere without free oxygen.
2. Formation of Ammonia, Water, and Methane: As the primitive
atmosphere cooled, lighter elements like hydrogen, carbon, nitrogen,
and sulfur reacted to form chemicals like CH4, NH3, H2O, and H2S.
3. Formation of Simple Organic Molecules: Condensation, polymerization,
and other reactions led to the formation of simple organic molecules like
amino acids, monosaccharides, fatty acids, and more.
4. Formation of Complex Organic Molecules: Polymerization resulted in
complex molecules like polysaccharides, proteins, nucleotides, and
nucleic acids.

6. Chemical Evolution of Life
5. Formation of Nucleic Acids: Nucleotides, the building blocks of
nucleic acids (RNA and DNA), may have formed from the reaction of
phosphoric acid, sugar, and nitrogenous bases.
6. Formation of Protobionts or Procells: Protobionts, the first form of
life, emerged from nucleic acids, organic, and inorganic molecules.
These were colloidal aggregations of lipids and proteins with some
properties of living systems.
7. Formation of First Cell: The development of RNA or DNA systems
within protocells resulted in the first cells resembling bacteria or
viruses. These cells were anaerobic, heterotrophic, and obtained
energy through chemoheterotrophic processes.

8. PROTOBIONTS ( ORIGIN OF LIFE)
• Definition: Protobionts are prebiotic chemical aggregates with some
properties of living systems.
• Formation: Resulted from the aggregation of organic molecules,
such as lipids and proteins, in a colloidal form.
• Coacervates: One type of protobiont, consisting of hydrophobic
proteins and lipids, forming lipoid bubbles.
• Microspheres: Another type, composed of colloidal hydrophilic
complexes surrounded by water molecules, often with a double-
membrane structure.
• Properties: Shared some basic features with living cells, including
growth and division.
• Transition to Eobionts/Protocells: Protobionts were the precursor
to the first primitive living systems known as eobionts or protocells.

10. Redis Experiment (Spontaneous Generation)
• Objective: To test the theory of spontaneous generation.
• Method: Francesco Redi placed meat in covered and uncovered
containers to observe if maggots would spontaneously appear on the
uncovered meat.
• Result: Maggots only developed on the uncovered meat, supporting
the idea that life did not arise spontaneously from non-living material.

11. Redi’s Experiment

12. Louis Pasteur Experiment (Disproving
Spontaneous Generation)
• Objective: To challenge the theory of spontaneous generation.
• Method: Louis Pasteur used swan-necked flasks with broth,
heated to sterilize, and observed if microbial growth occurred.
• Result: Microbial growth only occurred when the flasks were
exposed to air, showing that life did not spontaneously arise
from sterile solutions and supporting biogenesis (life from pre-
existing life).

14. Urey and Miller’s Experiment
• Objective: To provide experimental evidence for the chemical
evolution theory and Oparin's ideas.
• Apparatus: Spark-discharge apparatus, a glass chamber containing
sterilized and evacuated conditions.
• Gases Used: Methane (CH4), ammonia (NH3), and hydrogen (H2)
in the proportion of 1:2:2.
• Simulation: Electric discharge (mimicking lightning) through a
carbon arc spark, evaporation, and precipitation.
• Result: After several days of exposure to electric discharge,
condensation led to the formation of simple organic compounds like
urea, amino acids, and lactic acid.
• Implication: Strongly supports the idea that simple molecules in
Earth's early atmosphere could combine to form the organic building
blocks of life.

16. RNA WORLD HYPOTHESIS
• Origin: Proposed by Carl Woese, Francis Crick, and Leslie Orgel in
1960.
• Idea: Early life was likely based exclusively on nucleic acids,
particularly RNA.
• Ribozymes: Discovery of ribozymes (catalytic RNAs) by Sidney
Altman and Thomas Cech in 1989 provided crucial support.
• RNA Properties: RNA is structurally related to DNA, can evolve,
undergo mutations, replicate, and catalyze reactions.
• Role in Cells: RNA is abundantly present in living cells and plays a
significant role, including in ribosomes (protein assembly units).
• Evolution: RNA molecules may have replicated, mutated,
developed protein coats, and evolved into primitive cells. Eventually,
DNA might have formed, leading to Earth's biodiversity.

18. ORGANIC EVOLUTION
• Definition: Organic evolution is the process of slow, gradual,
continuous, and irreversible changes through which complex present-
day life forms developed from their simpler pre-existing forms.
• Evolution Principle: Evolution involves orderly changes from one form
to another, resulting in descendants being different from their
ancestors.

19. Darwin’s Theory of Natural Selection
• Darwin's Definition of Evolution: "Descent with modification."
• Overproduction: Prodigality of nature leads to the production of more
offspring in geometric ratios to ensure species' perpetuation.
• Struggle for Existence: Overproduction results in a struggle for limited
resources, food, environmental conditions, space, or to escape from
predators.
• Organic Variations: Variations occur in morphology, physiology, nutrition,
behavior, and other characteristics, providing the raw material for
evolution.
• Natural Selection: Favored variations better adapted to their environment
are selected by nature, while those with unfavorable variations perish. Also
known as "survival of the fittest."
• Origin of New Species (Speciation): Over time, successive generations,
with favorable adaptations and new modifications, give rise to new
species.

20. Strongest survives
Darwin’s finches

21. Objections to Darwin’s Theory:
• Fluctuating Variations: Darwin considered
minute, non-heritable, fluctuating variations
as principal factors of evolution.
• All Variations Are Heritable: He did not
distinguish between somatic and germinal
variations, assuming all variations were
heritable.
• Arrival of the Fittest: He did not explain how
the "fittest" variations arise.
• Neutral Flowers and Hybrid Sterility:
Darwinism did not account for the existence
of neutral flowers or the sterility of hybrids
• Cause, Origin, and Inheritance of
Variations: Darwin did not explain the cause,
origin, and inheritance of variations or the
existence of vestigial organs.
• Extinction of Species: The theory did not
explain the extinction of species.
• Intermediate Forms: The theory lacked
recognition of intermediate forms in many
cases.

22. MUTATION THEORY
• Proposed by: Hugo de Vries in 1901, after the rediscovery of Mendel's work in
1900.
• Observation: De Vries studied seven generations of the evening primrose
(Oenothera Lamarckiana) and found that some offspring displayed sudden,
discontinuous variations distinct from their parents' phenotypes, termed
mutations.
• Inheritance: Mutations were inheritable, as variant offspring produced variants,
not normal plants.
• Key Features:
• Mutations are large, sudden, and discontinuous variations within a population.
• These changes are inheritable.
• Mutations provide the raw material for organic evolution.
• Mutations can be useful or harmful, with useful mutations being selected by nature.
• Accumulation of mutations over time leads to the origin and establishment of new species.
• Harmful mutations may persist or be eliminated by nature

23. OBJECTIONS TO MUTATION THEORY
i. Chromosomal Aberrations: Large and discontinuous
variations observed by de Vries were often due to chromosomal
aberrations, whereas gene mutations typically result in minor
changes.
ii. Slow Mutation Rate: The rate of mutation is comparatively
slow in comparison to the pace required for evolution.
iii. Chromosomal Aberrations' Significance: Chromosomal
aberrations are often unstable and have limited significance in
evolution.

24. Modern Synthetic Theory of Evolution
• Synthesis of Biological Disciplines: Result of integrating various biological
disciplines like genetics, ecology, anatomy, geography, paleontology, etc. to
explain the mechanisms of evolution.
• Key Contributors: Scientists like R. Fischer, J. B. S. Haldane, T. Dobzhansky, J.
Huxley, E. Mayr, Simpson, Stebbins, Fisher, Sewall Wright, Mendel, T. H.
Morgan, and others played vital roles in developing the modern theory of
evolution.
• Key Factors: Five key factors discussed, including gene mutations, mutations in
chromosome structure and number, genetic recombinations, natural selection,
and reproductive isolation, contribute to the evolution of new species.
• Mendelian Population: Populations are composed of interbreeding groups, and
a small interbreeding group within a population is termed a "Mendelian
population."
• Gene Pool: The total genetic information encoded in the sum of genes within a
Mendelian population is referred to as the gene pool.
• Gene Frequency: The proportion of an allele in the gene pool to the total number
of alleles at a given locus is called gene frequency.

26. GENETIC VARIATION
• Gene Mutation: Sudden, permanent heritable changes that can occur within a
single gene (point mutation) or affect the chromosome or chromosome number.
These mutations lead to changes in the organism's phenotype, causing
variations.
• Genetic Recombination: In sexually reproducing organisms, genetic material
exchange happens during gamete formation through crossing over, leading to
new genetic combinations and phenotypic variations.
• Gene Flow: Movement of genes into or out of a population, whether by migration
of organisms, gametes, or DNA segments, altering gene frequency and causing
evolutionary changes.
• Genetic Drift: Random fluctuations in allele frequency within a natural population
due to pure chance, often occurring in small populations, leading to changes in
gene frequency.
• Chromosomal Aberrations: Structural changes in chromosomes due to
rearrangement, including deletion, duplication, inversion, and translocation, can
alter gene arrangement and contribute to variation in the population.

27. CHROMOSOMAL ABBERATIONS
• Definition: Chromosomal aberrations refer to structural changes in
chromosomes, leading to variations in gene arrangement.
• Types of Chromosomal Aberrations:
• Deletion: Loss of genes from a chromosome, resulting in the absence of
specific genetic information.
• Duplication: Genes are repeated or doubled in number on a chromosome,
often leading to extra genetic material.
• Inversion: A segment of a chromosome breaks and reattaches to the same
chromosome in an inverted position due to a 180° twist. This rearrangement
does not result in a loss or gain of gene content.
• Translocation: Transfer or transposition of a portion of a chromosome or a
set of genes to a non-homologous chromosome. This can occur naturally due
to the presence of transposons in the cell.

29. NATURAL SELCLECTION
• Main Driver of Evolution: According to Darwin, natural selection is
the primary force behind evolution.
• Genetic Variations: Genetic variations occur within a population.
• Favoring the 'Fittest': Organisms with traits making them more 'fit'
for their environment have a selective advantage, increasing their
likelihood to produce offspring.
• Differential Reproduction: Better-adapted organisms produce more
offspring in the population.
• Evolutionary Changes: Natural selection leads to changes in gene
frequency from one generation to the next, favoring traits that
enhance survival and reproduction.

30. NATURAL SELECTION
• Selection Against Harmful Mutations: Harmful mutations are
selected against, maintaining a mutation balance where the
frequency of harmful recessive alleles remains constant.
• Adaptive Efficiency: Natural selection promotes genes and traits
that ensure a high degree of adaptive efficiency between a
population and its environment.
• Industrial Melanism Example: Industrial melanism in moths, such
as Biston betularia and Biston carbonaria in Great Britain, illustrates
natural selection. Before industrialization, white-winged moths were
more abundant, as they could camouflage well on lichen-covered
trees, escaping from predatory birds. However, industrial pollution
blackened the trees, giving an advantage to black-winged moths.
Natural selection led to the shift in the population of moths based on
their camouflage against changing environmental conditions.

31. Moths: Biston species due to industrial melanism

32. Isolation
• Definition: Isolation refers to the separation of a population of a
particular species into smaller units, preventing interbreeding.
• Isolating Mechanisms: Barriers that prevent gene flow or the
exchange of genes between isolated populations are known as
isolating mechanisms.

33. Types of ISOLATION
I. Geographical Isolation:Also called physical isolation.
Occurs when a population is divided into two or more groups by
geographical barriers like rivers, oceans, mountains, glaciers,
etc.
Prevents interbreeding between isolated groups.
Exposed to different environmental factors, isolated populations
acquire new traits through mutations, leading to distinct gene
pools and the formation of new species (e.g., Darwin's Finches).
II. Reproductive Isolation:
Occurs due to changes in genetic material, gene pool, and
genital organ structure, preventing interbreeding between
populations.

34. Geographic
isolation
Reproductive
isolation

35. Types of ISOLATION MECHANISMS
A. Pre-mating or Pre-zygotic Isolating Mechanisms:
i. Habitat Isolation (Ecological Isolation): Population members live in the
same geographic region but occupy separate habitats, preventing potential
mates from meeting.
Ii. Seasonal or Temporal Isolation: Population members in the same region
are sexually mature at different times or during different parts of the year.
Iii. Ethological Isolation: Specific mating behaviors lead to members of the
population not mating.
Iv. Mechanical Isolation: Differences in the structure of reproductive organs
prevent mating between two populations.

36. Types of ISOLATION MECHANISMS
B. Post-mating or Post-zygotic Barriers:
i. Gamete Mortality: Gametes have a limited lifespan, and if
the union of two gametes does not occur within a certain time,
gamete mortality results.
ii. Zygote Mortality: While the egg may be fertilized, the zygote
dies for various reasons.
iii. Hybrid Sterility: Hybrids mature but become sterile due to
issues with proper gametogenesis (meiosis). For example,
the mule is a sterile intergeneric hybrid.

37. Mechanism of Organic Evolution
The following are the fundamental processes that bring about evolution:
1. Mutations:
Permanent heritable changes in the genetic material of an organism.
Gene mutations produce new alleles, which are added to the gene pool.
2. Gene Recombination:
Variations produced due to the coming together of alleles during sexual reproduction.
Gene recombinations occur due to the random union of gametes, anaphasic separation of chromosomes,
and crossing over.
3. Gene Flow:
The transfer of genes during interbreeding of populations that are genetically different.
Gene flow occurs due to emigration and immigration and brings about changes in allele frequency.

38. MECHANISM OF ORGANIC EVOLUTION
• Any alteration in allele frequency in a natural population by chance.
• Genetic drift is random or directionless and is more significant in small
populations than in large populations.
• It can lead to the loss or reduction of some alleles and the increase of
others.
• The founder effect occurs when a few individuals become isolated from a
large population and produce a new population with different allele
frequencies.
• The bottleneck effect happens when much of a population is killed due to
a natural disaster, leaving only a few individuals to start a new population.
4. Genetic Drift:

39. FOUNDERS EFFECT

40. MECHANISM OF ORGANIC EVOLUTION
5. Natural Selection:
The process by which better adapted individuals with useful variations are selected
by nature and leave more progeny (differential reproduction).
#Types of Natural Selection:
A. Stabilizing Selection (Balancing Selection): Favors intermediate forms, reduces
variations, and maintains phenotypic stability within the population.
B. Directional Selection: Favors one extreme of the phenotypic range and
eliminates the other, resulting in an evolutionary trend within the population.
C. Disruptive Natural Selection: Selects for extreme phenotypes at both ends of the
distribution curve, creating two peaks in the distribution of traits.

42. Hardy- Weinberg’s Principle
• Hardy-Weinberg's principle, also known as the Hardy-Weinberg equilibrium law, describes
the conditions under which the gene (allele) and genotypic frequencies in a population
remain constant from generation to generation. This equilibrium occurs under specific
conditions, including:
1. A large population: The population must be sufficiently large to reduce the effects of
chance fluctuations in allele frequencies.
2. Random mating: Individuals in the population must mate randomly, without any
preferences for particular genotypes.
3. No selection: No factors, such as natural selection, can favor specific alleles or
genotypes over others.
4. No migration: There should be no gene flow into or out of the population, meaning that
no new alleles are introduced or lost due to migration.
5. No mutation: Mutation rates must be low enough that they do not significantly alter
allele frequencies.
6. No genetic drift: The population size should be large enough to minimize the effects of
genetic drift, which is the random change in allele frequencies due to chance events.

43. Hardy- Weinberg’s Principle
The Hardy-Weinberg principle is expressed mathematically by the equation:
p² + 2pq + q² = 1
Where:
p² represents the frequency of homozygous dominant individuals (genotype AA).
2pq represents the frequency of heterozygous individuals (genotype Aa).
Q² represents the frequency of homozygous recessive individuals (genotype aa).
The sum of these genotypic frequencies (p² + 2pq + q²) equals 1, reflecting the fact
that all possible genotypes account for the entire population.

44. Hardy- Weinberg’s Principle
In the Punnett square:
A represents the dominant allele (p).
A represents the recessive allele (q).
The different combinations of alleles in the offspring (in the boxes of
the Punnett square) show how the frequencies of genotypes are
maintained within the population. If the conditions of the Hardy-
Weinberg equilibrium are met, then the gene and genotypic
frequencies will remain constant from generation to generation, and
the population will be considered genetically stable and non-evolving.

46. ADAPTIVE RADIATION
• Adaptive radiation is the process of evolution that leads to the
diversification of a single ancestral species into multiple new
species, each adapted to different ecological niches or
environments.
• Two well-known examples of adaptive radiation are:
• Darwin’s Finches: Charles Darwin’s observations of finches on the
Galapagos Islands illustrate adaptive radiation. The finches had a common
ancestor but adapted to various food sources and ecological niches on
different islands, leading to the development of distinct beak shapes and
feeding strategies
• Australian Marsupials: Australia’s marsupial mammals, including
kangaroos, koalas, and wombats, are descendants of a common ancestral
marsupial. Over time, they adapted to different environmental conditions,
leading to the diversification of marsupial species.

48. EVIDENCES OF EVOLUTION
A. Palaeontology:
• Study of ancient life through fossils.
• Fossils are preserved remains of past organisms.
• Fossils found in sedimentary rocks, amber, ice, and peat bogs.
• Primitive forms found in older layers, advanced forms in newer
layers.

49. Types of Fossils:
Actual remains: Preserved organisms (e.g., Wooly
Mammoth).
Moulds: Impressions left by decaying organisms.
Casts: Hardened mineral matter in mould cavities.
Compressions: Thin carbon film outlines external
features.

50. CONNECTING LINK: Archaeopteryx
• Archaeopteryx is called a connecting link between reptiles and birds
because it exhibits both reptilian and avian characteristics, which indicate
the transitional stage in evolution:
• Reptilian Traits:
• Long tail.
• Claws and scales on the body.
• Single-headed ribs.
• Abdominal ribs resembling those of a crocodile.
• Jaws with homodont teeth.
• Sternum without a keel.
• Solid (non-pneumatic) bones.
• Hind limbs with four clawed digits.

51. • Avian Traits:
• Feathery exoskeleton.
• Forelimbs modified into wings.
• Jaws modified into a beak.
• Completely fused skull bone.
• Large rounded cranium.
• Cranium with large orbits and a single condyle.
• Limb bones bird-like.
• Hind limbs with four toes, including one opposable toe.
CONNECTING LINK: Archaeopteryx

52. Significance of Palaeontology:
• Helps reconstruct phylogeny.
• Studies structures of extinct animals.
• Provides evidence for transitional forms (connecting links).
• Offers insights into the habits of extinct organisms.
• Indicates evolutionary line and relationships (e.g., Seymouria,
Archaeopteryx).

53. B. Morphology and Anatomy:
• Morphology: Study of external structures.
• Anatomy: Study of internal structures.
• Homologous organs: Structurally similar but functionally
different (e.g., vertebrate forelimbs).
• Analogous organs: Structurally dissimilar but functionally
similar (e.g., wings of insects and birds).
• Vestigeal organs: Imperfectly developed, non-functional
structures (e.g., vestigial nictitating membranes, wisdom teeth,
coccyx, appendix).

54. B. Morphology and Anatomy:

55. C. Molecular Evidences:
• Cells are basic units of life in all organisms.
• Similarities in proteins and genetic material (common ancestry).
• Basic metabolic activities occur similarly.
• ATP is the universal energy source.

56. Speciation:
• Definition: The process of forming new species from pre-existing species.
• Types of Speciation:
• Intraspecific Speciation:
• Allopatric Speciation: Occurs when a population is separated by a geographical
barrier.
• e.g., Galapagos finches due to geographical isolation.
• Sympatric Speciation: Takes place within a single population without geographical
isolation.
• e.g., Cichlid fishes in Lake Victoria, often driven by mutations.
• Interspecific Speciation:
• Hybridisation: Occurs when two different species crossbreed to produce a new
species.
• e.g., Mule (donkey and horse hybrid), Hinny (horse and donkey hybrid).

57. Interspecific
Speciation:
HYBRIDIZATION

59. Geological Time Scale:
• Purpose: Helps understand Earth's history and the evolution of
life.
• Divided into 6 Major Eras: (main four eras are: )
• Precambrian (4.6 billion to 541 million years ago)
• Paleozoic (541 to 252 million years ago)
• Mesozoic (252 to 66 million years ago)
• Cenozoic (66 million years ago to the present)

60. Geological Time Scale:
• Eras Divided into Periods and Epochs: Based on significant events.
• First Life: Appeared about 2,000 million years ago.
• Evolution of Life: Started in the sea and gradually diversified.
• Fish to Land Transition: Lobefin fish adapted to terrestrial life,
including coelacanths.
• Reptiles: Evolved from amphibians, becoming the first true land
vertebrates.
• Dinosaur Dominance: Dinosaurs once ruled the Earth but went extinct
around 65 million years ago.
• Rise of Mammals: Mammals replaced dinosaurs, showing intelligence
and adaptability.
• Continental Drift: Major disturbances like continental drift shaped
evolution by changing habitats.
• Unique Evolution: Human beings represent the pinnacle of
evolutionary history.

62. Human evolution
• Origin in Paleocene Epoch: Descended from tree-dwelling shrew-like
animals.
• Transition from Forests to Land: Arboreal mammals adapted to land due
to dwindling forests.
• Closest Relatives: Gibbons, chimpanzees, and gorillas are our closest
relatives.
• Key Evolutionary Trends:
• Increase in brain size and complexity, enhancing intelligence.
• Increase in cranial capacity.
• Development of bipedal locomotion (walking on two legs).
• Opposable thumb for better tool use.
• Erect posture and shortened forelimbs.
• Broadened pelvic girdle.
• Development of chin.
• Lumbar curvature.
• Social and cultural development (language, art, tools, etc.).

64. Human evolution
• Cranial Capacity Increase: Larger frontal lobe contributed to
higher intelligence.
• Physical Development: Adaptations allowed better use of
hands and motor skills.
• Bipedal Locomotion: Upright posture and stereoscopic vision
facilitated safe land movement.
• Evolutionary History Traced: Fossil remains revealed gradual
changes in cranial capacity, skull shape, and dentition.
• Ongoing Evolution: Human evolution continues to this day.