EVOLUTION

 Evolution is unrolling or unfolding of nature that brings about an orderly

change from one form or condition to another resulting in descendents
becoming different from ancestors. Evolution is rather a law of nature
 Evolutionary biology is the study of history of development of newer forms of
life from the pre-existing ones in various periods of time on earth

ORIGIN OF UNIVERSE

 Universe or cosmos is the whole existing space and matter which is

differentiated into several galaxies with each galaxy having several stars and
cloud of gas and dust
 Most accepted theory to explain the origin of universe is the Big Bang theory
which was proposed by Abbe Lemaitre in 1931. According to this theory,
universe has an explosive beginning. The universe expanded and hence
temperature came down

ORIGIN OF SOLAR SYSTEM

 According to Nebular Hypothesis of Kent, our solar system was probably

created about 4.5 to 5 billion years ago when gaseous cloud called solar
nebula was formed
 Our earth was supposed to have been formed about 4.5 billion years back.
There was on atmosphere on early earth

ORIGIN OF LIFE ( Biopoiesis)

 As far as we know life occurs only on earth though there is possibility of its
presence elsewhere as well. Methane which has helped develop life on earth
occurs on Jupiter, Saturn and interstellar space. Water has been detected on
our moon, on mars

Theory of special creation

Life was created by god

(i) Genesis of Bible has proposed that god created the world in six days
Day 1: Heaven and earth
Day 2: Sky and water
Day 3: Land and land plants
1
EVOLUTION www.spiroacademy.com
Day 4: Sun, moon and stars
Day 5: Birds and fishes
Day 6: Land animals and human

The first man was Adam. He was created from clay. The first woman was Eve who
developed from 12th rib of Adam

(ii) Hindu mythology – Hindu believed that the world was created by Brahma.
The humans were formed from his head, birds from chest, goats from
mouth and plants from hair. The first man was Manu and the first woman
was Shradha
 Theory of eternity
Different living beings, plants, stars etc. existed as such from the beginning
and would continue
 Theory of catastrophism
This theory was supported by Cuvier (1826), a French palacontologist, who
believed that the world has passed through many ages. A catastroph
occurred at the end of each age, which killed most of the living beings and
at the beginning of next new age, a new creation evolved
 Theory of cosmozoic origin
Both living and non-living matters were formed simultaneously. Early living
objects were resistant spores call cosmozoa. Cosmoza gave rise to different
types of living beings on earth
This theory was given by Richter in 1865.
 Theory of Panspermia
Arrhenius (1908) proposed the theory of directed panspermia. The salient
features are
(i) They assumed the presence of advanced civilization on other planets in
our galaxy.
(ii) Life on earth and many other planets were infected from these
advanced civilized planets
(iii) Directed panspermia theory was supported by genetic code
 Theory of spontaneous generation
It originated in Egyptian civilization. Greek philosophers believed in it.
Anaximander thought life to arise from much warmed by sun. Aristotle
believed plants to developed from soil while worms and snails to be products
of putrefaction. Frog were believed to arise from moist soil
Van Helmont had claimed origin of mice both sexes from human sweat and
wheat bran kept in dark for 21 days
2
EVOLUTION www.spiroacademy.com

Biogenesis
 Theory of spontaneous generation was disapproved through the finding that
life comes from pre-existing life
 Francesco Redi ( 1668) placed thoroughly cooked meat in three jars (i)
Uncovered (ii) covered with parchment (iii) covered with muslin.
Maggots developed only in uncovered jar. No maggot developed in jar
covered with parchment. Flies visited third jar and laid egg on muslin. Egg
fallen in jar produced maggots.
 Spallanzani ( 1765) boiled nutrition in glass flasks, sealed the flasks and kept
them. The broth remained clear indefinitely with no signs of living beings
 Pasteurs (1862) took broth in flasks straight and swan ( bent S –shaped) necks,
boiled and allowed the broth to cool. No germ developed in the broth it was
connected with atmosphere through curved neck of the flask. The dirt
particles could not reach the broth because they got trapped in bend of neck.
When swan neck were broken, broth developed colonies of microorganisms
showing that the same have come from air. The same happened in straight
necked flasks

MODERN HYPOTHESIS OF ORIGIN OF LIFE

Chemical origin of life ( chemogeny)
 Oparin suggested that from the simple compound like nitrides, oxides,
ammonia, methane complex organic compounds were formed gradually
under the influence of electric charges, ultra-violet rays
 First , were the formation of hydrocarbons, like acetylene, ethylene etc. these
then form oxy and hydroxyl derivatives forming aldehydes, ketones and acids,
sugar and starch were the main products.
 Miller’s experiment – Stanley Miller (1953)a graduate student of Harold C
Urey designed an apparatus for stimulating condition prevalent on earth at
the time of abiogenic evolution of organic substances. The apparatus has a
spark chamber with two electrodes, a flask for boiling and a condenser. A
control apparatus was also prepared but without electrodes in spark chamber
 Milller used a mixture of methane ammonia, hydrogen and water. The
mixture was exposed to electric discharges, following by condensation and
then boiling. It was continued for 18 days.
 Miller was able to identify 15 amino acids, organic acid, ribose sugar and
purine, adenine.

3
EVOLUTION www.spiroacademy.com
 The formation of protein molecule is considered a land mark in the origin of
life

Biological evolution

 Formation of proteinoids: Protinoids are molecules which are obtained by

synthesizing polypeptides by heating a mixture of amino acids at 160 – 210oC
for several hours.
 Formation of coacervates
When macromolecules were formed they undergo aggregation and
precipitation in the sea, which led to the formation of organized structures
were distinct bodies, which did not mix with the surrounding sea – water.
They contained proteins, nucleoproteins and other organic and inorganic
molecules in various reactions. The surface layer of the coacervates had ability
for selective absorption of substances from the medium. Oparin considered
the coacervates as the sole living molecules which gave rise to cells
 Formation of precells or protocells.: The protocells were spherical in shape
and a double layered membrane was present around them. They exhibited
reproduction by binary fission. The proto cells were heterotrophs; they
obtained the energy formed by the fermentation of organic molecules which
gave rise to cells
 Formation of precells to cells: When DNA – RNA system developed within
protocells, they looked like a bacteria or virus. The DNA acquired the ability
for self duplication and protein synthesis. Thus life originated after a long
process of molecular evolution. The proto cells in course of time differentiated
into cells

4
EVOLUTION www.spiroacademy.com

EVIDENCE OF EVOLUTION

 The convincing evidences for the occurrence of descent with modification

come from
(i) Paleontology
(ii) Morphology and comparative anatomy
(iii) Embryology
(iv) Geographical distribution
(v) Taxonomy
(vi) Connecting links
(vii) Cytology
(viii) Biochemistry
(ix) Genetics

Evidences from paleontology

 Paleontology is the study of past life based on fossil records. Their study
reveals the existence of life in past and illustrates the course of evolution of
plants and animal

5
EVOLUTION www.spiroacademy.com
 Leonardo da vinci is considered father of paleontology while George Cuvier is
called father of modern paleontology
Types of fossils
(i) Body fossils: These are hard parts of an organism, which provide details
of shape and function of actual organism such as bone, tooth, skull etc.
(ii) Subfossils: These are the remains of plant and animals which were
formed during Holocene period after the last ice age and found
preserved in rocks formed after 10,000 years.
(iii) Microfossils : Microscopic fossil remains of animals and plants usually
less than 0.5 mm size are known as microfossils.
(iv) Macrofossils: Fossils of larger than one cm size such as corals, skeleton
(v) Pseudofossils: these are inorganic origin objects, which show close
resemblance with the forms of organic origin and are found in
sedimentary rocks.
(vi) Unusual fossils: Fossils formed as a result of combination of events and
condition which results in all or most of the organism getting preserved
in rock.
(vii) Trace fossils: these are fossils of foot prints and trail left in mud by past
living organisms such as dinosaur’s foot print
(viii) Coprolites : These are trace fossils of dropping of animals or faecal
matter, either very small like faecal pellets of sea snail or large
coprolites of dinosaurs, crocodiles and mammals

Determination of age of fossils

Carbon dating – radio active C-14 occurs naturally. It enters food chain and is
therefore found in all living beings and their remains. Half life of C-14 is 5730 years.
Carbon dating can measure articles upto 25,000 years old

Evidences from morphology and comparative anatomy

(a) Homology ( Divergent evolution)

 Homology is the similarity between organs of different animals based on
common ancestry and built on same fundamental pattern, but perform varied
function
Examples
(1) The flipper of seal, wing of bat front leg of horse and arm of man shows
homology

6
EVOLUTION www.spiroacademy.com
(2) Thorns of Bougainvillea and tendrils of Passiflora are modified branched
but thorns of Bougainvillea are for protection while tendrils of Passiflora
are for climbing

Presence of homologous organ in different group confirms

 Common ancestry and relationship between different groups

 Difference in appearance due to divergent evolution
(b) Analogy ( Convergent evolution)
 Analogy is the difference in basic structure and origin but are adapted to
perform similar functions Examples:
1. Fines of fishes and flippers of whale. Similar appearance and function but
their structural designs are different
2. Wings of butterfly and bat serve the same purpose i.e. flight, but wings of
insect is formed of a thin flap of chitin and stiffened by series of veins.
Where as in bat wing is formed of a fold of integument, supported by the
elongated and outspread phalanges.
(c) Adaptive radiation
 The process of evolution of different species in a given geographical area
starting from a point and literally radiating to other areas of geography is
called adaptive radiation.
Example: Australian marsupials. A number of marsupials, each different from
other evolved from an ancestral stock, but all within the Australian island
continent

Embryology

Embryology is the study of formation and early development of an individual from

zygote to young ones

(1) Similar early development early embryo development is similar in animals

passing through morula ( solid ball), blastula ( two layered) stages showing
their common origin
(2) Resemblance amongst vertebrate embryos. Embryos of all vertebrates pass
through fish like state having somites, gill clefts / slits behind neck, tail,
notochord
(3) Development of vertebrate organs . Heart of a mammal or bird is initially two
chambered ( as in fishes), three chambered ( as in amphibians) and then four
chambered
(4) In seventh month of pregnancy human foetus resembles a baby ape

7
EVOLUTION www.spiroacademy.com
(5) Recapitulation theory / Biogenetic law
Meckel ( 1810) proposed that developing animal embryo passes through
stages resembling adult forms of its ancestors

Evidences from Geographical distribution

 The degree and period of separation of an area from another correspond to

species diversity
 Double coconut occurs only in seychelles island. Kangaroo and Koala are
marsupials found in Australia
 Darwin observed that the finches on mainland of America were all of one
type, possessing short straight beaks for seed crushing. These birds from
Galapagos island differed in size and shape due to different food types
available. Some were vegetarian finches, warbler finches while others were
insectivorous finches

Evidences from taxonomy

Depending upon their resemblances and differences, living organisms are divided
into groups i.e. monera, protista, fungi, plantal and Animalia. The common
characters present in a species, genus, family, class or phylum indicate common
ancestry while the difference indicate evolution.

Evidences from connecting links

While classifying animals one comes across certain animals or small animal groups
which exhibit characteristics of more than one group. Such animals or animal group
are called connecting links between those two groups

Example: Euglena

A connecting link between animal and plant. Some animal character of euglena are

(1) Body is covered by pellicle

(2) Reproduction is animal like some plants character of euglena are
(a) It is having chlorophyll and chloroplasts
(b) Nutrition is autotrophic
(c) It synthesis their food through photosynthesis

Evidences from cytology

(1) Protoplasm of all the organisms have carbon, hydrogen, oxygen and nitrogen

8
EVOLUTION www.spiroacademy.com
(2) DNA and rarely RNA is the genetic material in all the organisms, which show
common ancestry and origin of all organisms.
(3) The same genetic code have triplet codons is found from the viruses to man
and all living beings have same amino acids for same codon.

Evidences from biochemistry

 Living being posses similar types of biochemicals, biochemical reaction and

body functions
 Example, aerobic organisms perform Krebs cycle having similar types of
enzymes from chlamydomonas and amoeba to human being and peepal tree
 A - B blood grouping is present in apes as well as humans but not in monkeys
indicating a closer relationship between the former

Evidences from genetics

Accumulation of mutation produce new verities and races, e.g. red sunflower, dwarf
wheat etc. Hybridisation and induction of polyploidy has given rise to new plants

Four modern theories have been put forward to explain the mode of evolution.
These are

(i) Lamarck’s theory of inheritance of acquired characters or Lamarckism

(ii) Darwin’s theory of natural selection or Darwinism
(iii) De Vries mutation theory
(iv) Modern concept of evolution

Lamarckism or Inheritance of acquired characters

 Jean Baptiste de Lamarck was a French naturalist, well known for his theory of
evolution
 The central idea of Lamarckism is that the characteristics acquired by an
organism during lifetime in response to environmental conditions are passed
on to their offspring. The main points include
(i) Organisms and their organs have a natural tendency to continuously
increase in size, generation after generation
(ii) Continuous changes in the environmental conditions directly influence
the nature habits, way of living or organism and their structural
organism and their structural organization
(iii) The growth of less used parts decline, while that of better used parts
progresses

9
EVOLUTION www.spiroacademy.com
(iv) The growth of organs either better or poor acquired during lifetime of
an organism is heredity
 Examples of Lamarckism
(1) Giraffe – the ancestors of giraffe were bearing a small neck and fore –limbs
and were like horses, but as they were living in places with no surface
vegetation, they has to stretch their necks and forelimbs in order to eat
leaves from trees
(2) Flightless birds : The development of flightless birds like ostrich from flying
ancestors is considered due to continued disuse of wings as they were
found in well protected areas with plenty of food
(3) Snakes: The present day limbless snakes with long slender neck were
developed from the limbed ancestors. It is due to continued disuse of
limbs and stretching of their body to suit their creeping mode of
locomotion and fossorial mode of living
 Evidences in favour of law of inheritance of acquired characters are-
(1) During vegetative propagation of plants and regeneration in animals
somatic cells can produce the germ cells
(2) Sudden heritable variations or mutations were obtained by Auerbach et. Al
on exposure of Drosophila to high energy radiations like UV – rays, X-ray,
γ-ray and mustard gas etc.
 Lamarckism or theory of inheritance of acquired characters was discarded due
to following reasons
(1) Blind, deaf and lame parents do not produce abnormal offspring
(2) Despite of use of iron shoes to keep their feet short by Chinese women,
their young ones at birth have normal feet size
 These criticism lead to the foundation of Neo-Lamarckism
The postulates of Neo-Lamarckism are
(1) According to Neo-Lamarckism, there is causal relationship between the
structure, function and environment
(2) Some of the variations acquired by an individual can be transmitted to its
offspring
(3) The role of internal vital forces in evolution has been discarded
(4) Only those variations are inherited, which are associated with the germ cells
or where the somatic cells give rise to germ cells
(5) It has been realized now that the body character of organisms are related to
result of interaction of genes and the environmental conditions

10
EVOLUTION www.spiroacademy.com
Darwin’s theory of natural selection or Darwinism

 Charles Darwin was born in 1809. In 1831, he accepted an unpaid post of

naturalist on the survey ship, i.e. HMS Beagle, in which he spent five years in
sea charting the East coast of South America
 Features of theory of natural selection are
(1) Overproduction : Organisms have a very high reproductive potential and
capacity , multiply in geometric ratio.
(2) Limitations of food and space: The resources of earth are limited.
Therefore, populations of different species cannot increase beyond a
certain limit.
(3) Struggle for existence: A struggle or competition occurs amongst
organisms to obtain the available resources. It is of three types-
(a) Intra-specific struggle: This is the most acute type of struggle, which occurs
amongst individuals of the same species for similar basic necessities like
food, shelter, breeding place, light, water etc
(b) Inter-specific struggle: the struggle occurs amongst individuals of different
species for similar requirements like food, shelter
(c) Environmental struggle: The struggle is between organism and restricting
environmental factors like carrying capacity, drought, heavy rains, foods,
famine, earthquake, volcano, lightning, meteorite, etc.

Variations

 They are small morphological and behaviouristic differences amongst the

individuals. Variation can be continuous discontinuous, harmful.
 Darwin believed that continuous and useful variation constitute the raw
material of evolution. Neutral and occasionally harmful variations may also
prove helpful with the change of environment.

Natural selection and survival of the fittest:

In the struggle of existence, only those individuals survive which possess the most
useful variations. This has been called natural selection by Darwin and survival of the
fittest by Spencer

 This theory was criticized because

(1) Darwin did not explain the mechanism of origin of variations
(2) He did not know the mode of transmission of variations to the next
generation.

11
EVOLUTION www.spiroacademy.com
(3) Continuous variation cannot go beyond limit of species. Mutation are
actually the source of evolution
(4) Darwinism does not explain origin of variation, new characters
(5) It is unable to explain the persistence of degenerate organ and over-
specialisation ( e.g. tusk of elephant)
(6) There are certain organisms which have remained unchanged for the past
several million years
 Evidences in support of Darwinism are
(1) Evident facts: High rate of reproduction, limitation of resources,
abundance of variation are quite evident
(2) Entomophily: Many pollinating insects have proboscis length exactly
matching the position of nectary in flower. This may develop due to
natural selection.
(3) Mimicry: It is the resemblance of an organism with another or a natural
object so as to conceal itself for protection or some other advantage like
catching of prey. E.g. praying mantis, stick insect
(4) Extinct forms: Extinction of past plants and animals can be explained only
by development of better organisms through natural selection
(5) Adaptations: Variations present in the population help the individuals in
adapting themselves to changed environmental conditions. Adaptations
produce new ecotypes from which new forms can develop
(6) Artificial selection : It is a selective breeding of plants and animals so as to
obtain varieties with desired traits.
(a) Agriculture perhaps originated with selection of nonbrittle ear in
Triticum monococcum ( Einkorn wheat) This was later replaced by
naked and high yielding wheat
(b) Through artificial selection, wild cabbage has given rise to several
vegetables like Kale, kholrabi, cabbage, Cauliflower, Broccoli etc
(c) High milk yielding varieties of Buffalo have developed by monitoring of
animals producing more milk and breeding them with bulls of high milk
yielding lineage

Neo-Darwinism

 The theory of evolution as proposed by Darwin and Wallace has been

modified in the light of modern evidence from genetics, molecular biology,
palacontology, ecology and is known as neo-Darwinism
 Neo-Darwinism distinguishes the germplasm and somatoplasm

12
EVOLUTION www.spiroacademy.com
 It explained that adaptations result from the multiple forces and natural
selection is one of them
 As per Darwinism, characters are not inherited as such, instead there are
character determiners which control the development.
 The characters are the result of genes of organisms and the environment
during its development

De Vries mutation theory

 The term mutation was introduced by Hugo de Vries, a Dutch botanist who
independently rediscovered Mendel’s law of heredity
 Mutation theory was put forward by him in 1908
 Salient features of mutation theory are as follows
(1) Mutation acts as a raw material for evolution.
(2) Mutation are large heritable and subjected to natural selection
(3) Mutation are large heritable changes in contrast to small, directional
fluctuating variation of Darwin
(4) Mutation may occur in any direction and may be useful or harm
(5) Sometimes, new species are produced by a single mutation
(6) This theory has following criticism
1) D.M. Davis claimed that the Oenothera lamarckiana ( evening primrose)
was a hybrid plant, which could be obtained by the hybridization of two
wild species and is not normal plant
2) Natural mutation are not the common phenomenon
3) Most of the mutation are recessive
4) Development of mimicry cannot be explained satisfactorily
5) Theory failed to explain the role of nature

MODERN CONCEPT OF EVOLUTION

 The present concept of evolution is a modified form of Darwin’s and Hugo de

Vries theories. This is also called synthetic theory of evolution
 The main postulates of this theory are
(1) This theory recognizes four basic types of process. These are
(a) Gene mutation are changes in chromosome structure and number and
genetic recombination provide the genetic variation without which
changes cannot takes place and natural selection guides populations of
organism for adaptations.

13
EVOLUTION www.spiroacademy.com
(b) Migration of individuals from one population to another, hybridization
between races or closely related species both increase the genetic
variability
(c) Mutation, genetic recombination and natural selection are equally
important
(d) The effect of change, acting on small population may alter the way in
which natural selection guides the course of evolution.
(2) All sexually reproducing organisms contain a large gene pool of genetic
variability, which maintain a dynamic equilibrium between in flow and out
flow of genes
(3) Genes may be added to gene pool by immigration from other gene pool
and mutation.
(4) Genes are removed from the gene pool by natural selection and chance
elimination of alleles, which take place in small population or during
reduction of population size
(5) Genetic recombination following the principles of mendelian heredity is
constantly reshuffling the genes in the gene pool.
(6) Natural selection, which results from the interaction between populations
and their environment, may either stabilize gene composition by
eliminating most immigrants and mutants or change in various way
(7) Evolution takes place through alternations of the frequency of genes and
gene combination in the population brought about by natural selection
(8) Reproductive isolation, includes all the barriers to gene exchange between
the populations has a canalizing effect
(9) The populations that are reproductively isolated from each other are
almost certain to evolve in different directions while those that are not so
isolated because of gene exchange will evolve in the same direction

MECHANISM OF EVOLUTION

Hardy – Weinberg Law

 Hardy-Weinberg Law was proposed in 1908 by the independent contributions

of two scientists, Hardy ( England) and Weinberg ( Germany)
A clear understanding of gene pool and gene frequency
 Gene Pool
Gene pool is defined as “the sum total of genes present in a population ”or “A
gene pool comprises diverse from of a gene combination and recombination
by the process of sexual reproduction.”

14
EVOLUTION www.spiroacademy.com
 Gene frequency
The ratio of gene in a gene pool or in a population is called gene frequency
When the gene frequency of other allele in the population can be calculated
by applying simple formula. If the gene frequency of A – allele is p and a-allele
is q, the p+q =1
The frequency of AA individual in population is p2, of aa is q2 , of Aa is 2pq.
Hence p2+q2 +2pq = 1

Significance

- This law states that the gene frequencies in large population remains
constant generation after generation where there is no selection and
mutation. In small population, this equilibrium cannot be maintained
- When the population is large and in equilibrium rate of evolution is zero as
there is not possibility of evolutionary change

15
EVOLUTION www.spiroacademy.com
 Gene flow
Animals are not static. They have tendency to migrate and mate with inmate
of the population. Thus the genes of one population are transferred into
another population. This is called gene flow and are important source of
genetic variation
 Genetic drift
Genetic drift is an evolutionary force operating in small population
The change in the frequency of gene purely by chance is called genetic drift

HUMAN EVOLUTIONARY TRENDS

The gradual evolution of man from ape is fully supported by available fossils

1. Propliopithecus: It was an ape like primate, but in the possession of short

arms, it resembled man. It lived, about 30 million years ago
2. Aegyptopithecus: It is similar to propliopithecus. It is believed that it was
ancestral of Dryopithecus
3. Dryopitecus: It is a group of apes that lived about 20 million years ago. Their
forelimbs were shorter than hindlimbs. It is also ancestor of modern apes like
Chimpanzee and Gorilla
4. Oreopithecus : In the structure of teeth and erect walking, it resembles man,
but having long forelimbs, it resembles apes. Straus and simpson suggest that
man and oreopithecus have parallel evolution and hence are not ancestral to
man.
5. Ramapithecus: It lived 12 to 12 million years ago. The dentition is more
identical to dentition of man and their fossil were collected from Africa and
India
6. Kenyapithecus: It is closely related to Ramapithecus. Its fossil is collected from
East Africa.
7. Australopithecus: It is connecting link ape and man. It lived 2 to 5 million years
ago. The characters of Australopithecus like man and ape are as below
- Man like characters: Erect posture, bipedal locomotion and dentition is like
that of man
- Ape like characters: Teeth were larger than modern man, absence of chin,
eye brow ridges projected over the eyes
8. Homo erectus: It is erect ape man. They are commonly called Java man
because their fossils were collected from Java. They lived about 5,00,000 years
ago. The main characters of Homo erectus are
16
EVOLUTION www.spiroacademy.com
- They has upright bipedal locomotion
- They were slightly taller than Australopithecus.
- The face are chinless
- They used fire and variety of tools
9. Homo sapiens
(1) Neanderthal man: They existed about 75,000 years ago. The main
character are
- Their eyebrow ridges were heavy and protruding
- Their teeth were large
- They had no chin
- Their cranial capacity was about 1400 cc
(2) Rhodesian man: The fossils were collected from Rhodesia. The cranial
capacity was about 1300 cc
(3) Cro-magnon man: These were the men who lived in Europe during the last
30,000 years. They possessed all characteristics of modern man
(4) Modern man: They were originated 8000 years ago. The cranial capacity
of modern man is 1450cc
The main human races are:
(a) Caucasoid race
(b) Negroid race
(c) Mongoloid race
(d) American race
(e) Australian race
(f) Indian race

17