Presented by:

Mr. Srikanth A. V M.Sc., M.Phil.,

Lecturer in biology,

Sri Aurobindo PU (Ind) College,

Javalli, Shimoga

Beginning of LifeBeginning of Life

Our Planet Earth is believed to have Our Planet Earth is believed to have originated about originated about 4.6 billion4.6 billion years ago. years ago.The early life on earth is dated back to 3.5 The early life on earth is dated back to 3.5 billion years.billion years.None of the earliest known life forms exist None of the earliest known life forms exist today.today.With the concept of evolution, man With the concept of evolution, man becomes a part of nature, a relative of all becomes a part of nature, a relative of all living beings and a product of grand living beings and a product of grand natural process extending back to the natural process extending back to the dawn of the universe itself.dawn of the universe itself.

Origin of life: Important theoriesOrigin of life: Important theories

Theory of special creationTheory of special creation

Cosmozoic theory or Panspermia Cosmozoic theory or Panspermia theorytheory

Theory of AbiogensisTheory of Abiogensis

Theory of BiogensisTheory of Biogensis

Theory of Chemical EvolutionTheory of Chemical Evolution

Theory of Special CreationTheory of Special Creation

This is the oldest of all theoriesThis is the oldest of all theories All living beings on this earth were All living beings on this earth were

originally created by originally created by God or God or supernatural powersupernatural power

Supported by world’s major religions Supported by world’s major religions and civilizationsand civilizations

Science can neither prove nor disprove Science can neither prove nor disprove the theorythe theory

Biblical accountBiblical account

According to Spanish monk Father According to Spanish monk Father Suarez, creation of the earth by God is as Suarez, creation of the earth by God is as followsfollows

11stst Day- Created heaven and earth Day- Created heaven and earth 22ndnd Day- Separated sky and water Day- Separated sky and water 33rdrd Day- Made dry lands and plants Day- Made dry lands and plants 44thth Day- Made sun, moon and stars Day- Made sun, moon and stars 55thth Day- Created birds and fishes Day- Created birds and fishes 66thth Day- Created land animals and man Day- Created land animals and man

Cosmozoic theory or Cosmozoic theory or Panspermia theoryPanspermia theory

Put forth by Put forth by RichterRichter in 1865 in 1865Life on earth has come from a distant Life on earth has come from a distant planet in the form of spores or planet in the form of spores or microbes called microbes called cosmozoacosmozoa or or panspermiapanspermiaThese were believed to preserved in These were believed to preserved in meteorites and released to earth when meteorites and released to earth when they struck the earth’s surfacethey struck the earth’s surfaceFailed to prove the existence of life on Failed to prove the existence of life on distant planetdistant planet

Theory of Abiogenesis or Theory of Abiogenesis or Spontaneous generationSpontaneous generation

Put forth by Put forth by Greek PhilosophersGreek Philosophers in 600 BC in 600 BC

Life originated from non-living material Life originated from non-living material spontaneously and continuously.spontaneously and continuously.

Air, water, fire and earth have active Air, water, fire and earth have active principles or vital force to transform lifeless principles or vital force to transform lifeless matter into living things.matter into living things.

This view was held by scientists like This view was held by scientists like Aristotle, Epicurus, Thales, Helmont, Newton, Aristotle, Epicurus, Thales, Helmont, Newton, Decartes, etc.Decartes, etc.

AristotleAristotle Father of BiologyFather of Biology Active principle existed in Active principle existed in

all forms of lifeall forms of life Active principle present in Active principle present in

fertilized egg transforms it fertilized egg transforms it into an adult organisminto an adult organism

Children received active Children received active principles form their principles form their parents.parents.

Sunlight, mud and Sunlight, mud and decaying meat also had decaying meat also had the active principle.the active principle.

Some beliefs of AbiogenesisSome beliefs of Abiogenesis

Dirty shirt and wheat grains put together in a Dirty shirt and wheat grains put together in a dark cupboard produces mice in 21 days. dark cupboard produces mice in 21 days. ((Van HelmontVan Helmont))

Frogs and snakes arise from mud Frogs and snakes arise from mud spontaneously.spontaneously.

Horsehair falling into water develop into Horsehair falling into water develop into worms.worms.

A leaf falling into river would develop into A leaf falling into river would develop into wings and gradually transform into a duckwings and gradually transform into a duck

A dead calf buried would give rise to a swarm A dead calf buried would give rise to a swarm of bees.of bees.

Theory of BiogenesisTheory of Biogenesis

Put forth by Put forth by Francisco RediFrancisco Redi in in 1688 and supported by 1688 and supported by SpallanzaniSpallanzani and and Louis PasteurLouis Pasteur..

Life originates from pre-Life originates from pre-existing life by reproductionexisting life by reproduction

Spallanzani and Louis Spallanzani and Louis Pasteur’s experiment.Pasteur’s experiment.

Theory of Chemical EvolutionTheory of Chemical Evolution

Put forth by Put forth by Alexander. I. OparinAlexander. I. Oparin in 1924 who in 1924 who published his ideas in book entitled “The Origin Of published his ideas in book entitled “The Origin Of Life”.Life”.

J.B.S. HaldaneJ.B.S. Haldane supported it and therefore theory is supported it and therefore theory is also known as also known as Oparin-HaldaneOparin-Haldane theory theory

Life originated from non-living matter i.e., Life originated from non-living matter i.e., abiogenetically from inorganic substances.abiogenetically from inorganic substances.

The theory explains evolutionary sequence from The theory explains evolutionary sequence from inorganic compounds to organic compounds, to inorganic compounds to organic compounds, to macro molecules and primitive cell forms.macro molecules and primitive cell forms.

Alexander. I. OparinAlexander. I. Oparin

1. Origin of Earth1. Origin of Earth According to According to nebular theory or Bigbang theorynebular theory or Bigbang theory of of

Immanuel in 1755, our solar system originated about 5 Immanuel in 1755, our solar system originated about 5 billion years ago from a rotating cloud of gas called billion years ago from a rotating cloud of gas called nebulous.nebulous.

It exploded into several hot pieces called nebulae. It exploded into several hot pieces called nebulae. Earth is one such piece of the nebulae.Earth is one such piece of the nebulae.

It was very hot an had elements like Iron, Nickel, It was very hot an had elements like Iron, Nickel, Aluminium, Carbon, Hydrogen, Oxygen.Aluminium, Carbon, Hydrogen, Oxygen.

As it cooled, these elements condensed to form core, As it cooled, these elements condensed to form core, crust and atmosphere of the earthcrust and atmosphere of the earth

Earth, at that time (4.6 billion years ago) was lifeless Earth, at that time (4.6 billion years ago) was lifeless and inhospitable.and inhospitable.

2. Pre-biotic environment of the Earth2. Pre-biotic environment of the EarthPrebiotic earth had a reducing atmosphere due Prebiotic earth had a reducing atmosphere due to absence of molecular oxygen and the present to absence of molecular oxygen and the present day one is oxidizing one.day one is oxidizing one.Cooling changed it from gaseous to liquid and Cooling changed it from gaseous to liquid and then from a liquid to the solid. then from a liquid to the solid. The change from liquid to solid is not yet The change from liquid to solid is not yet complete and the earth’s core is still in molten complete and the earth’s core is still in molten condition.condition.When the temperature fell below 100When the temperature fell below 100ooC, water C, water vapors gradually condensed into liquid which vapors gradually condensed into liquid which resulted in heavy rainsresulted in heavy rainsPrimitive earth was a volcanic mass with heavy Primitive earth was a volcanic mass with heavy lightning, radiating heat from the centre of the lightning, radiating heat from the centre of the earth, high energy UV radiation from the sun and earth, high energy UV radiation from the sun and heat from radio active decayheat from radio active decay

Formation of Earth’s Formation of Earth’s crustcrust

Rock containing Rock containing various inorganic various inorganic salts and mineralssalts and minerals

3. Formation of monomers3. Formation of monomersIt was the first step towards origin of life and It was the first step towards origin of life and probably Methane played an important role.probably Methane played an important role.

In a pre biotic environment, simple inorganic In a pre biotic environment, simple inorganic molecules reacted to form simple organic molecules reacted to form simple organic compounds especially in the oceans.compounds especially in the oceans.

CHCH44+H+H22OO→sugars, fatty acids, glycerol→sugars, fatty acids, glycerol

CHCH44+H+H22O+NHO+NH33→amino acids→amino acids

CHCH44+H+H22O+NHO+NH33+HCN→nitrogenous bases+HCN→nitrogenous bases

HaldaneHaldane described the oceans containing this described the oceans containing this sterile mixture of simple monomers as sterile mixture of simple monomers as “the hot “the hot dilute soup” or “the primitive broth”.dilute soup” or “the primitive broth”.

4. Formation of Polymers4. Formation of Polymers The monomers collided, reacted and aggregated The monomers collided, reacted and aggregated

to form new complex molecules like to form new complex molecules like polysaccharides, fats, proteins, nucleosides and polysaccharides, fats, proteins, nucleosides and nucleotides.nucleotides.

This is said to be a This is said to be a ‘landmark in the origin of ‘landmark in the origin of life’life’

A borderline stage between living and non-living A borderline stage between living and non-living was reached by the union of nucleic acids and was reached by the union of nucleic acids and proteins to form nucleoproteins.proteins to form nucleoproteins.

Sugars+sugarsSugars+sugars→polysaccharides→polysaccharides Fatty acids+Glycerol→lipidsFatty acids+Glycerol→lipids Amino acids+amino acids→proteinsAmino acids+amino acids→proteins Nucleotides+nucleotides→nucleic acidsNucleotides+nucleotides→nucleic acids

5. Formation of coacervates5. Formation of coacervates

In some protected places, the In some protected places, the macromolecules aggregated as micro macromolecules aggregated as micro droplets inside a protective water repellent droplets inside a protective water repellent protein covering to from protein covering to from coacervatescoacervates. The . The formation of coacervates is known as formation of coacervates is known as coacervationcoacervationSydney FoxSydney Fox called them as called them as microspheresmicrospheres..Deamer and Hargreaves called them as Deamer and Hargreaves called them as liposomes.liposomes.

6. Formation of pre cells (Ebionts)6. Formation of pre cells (Ebionts)

The nucleic acids acquired self replicating ability. The nucleic acids acquired self replicating ability. These along with other inorganic and organic These along with other inorganic and organic substances gave rise to the first form of life substances gave rise to the first form of life called as ‘called as ‘protobiontsprotobionts’ or ‘’ or ‘precellsprecells’.’.These were prokaryotic type with lipid These were prokaryotic type with lipid membrane bound units with enzyme controlled membrane bound units with enzyme controlled mechanism nucleic acid regulation without mechanism nucleic acid regulation without organized nucleus.organized nucleus.They were heterotrophic anaerobes and were They were heterotrophic anaerobes and were getting their requirement from surrounding getting their requirement from surrounding organic contents organic contents

Coacervates theory of OparinCoacervates theory of Oparin

It was put forth by It was put forth by A.I.OparinA.I.Oparin in 1938. in 1938.

According to this theoryAccording to this theoryThe formation of membrane bound macromolecules into The formation of membrane bound macromolecules into coacervates is known as coacervation.coacervates is known as coacervation.

Coacervates were held together in the surrounding liquid Coacervates were held together in the surrounding liquid had a separation between themhad a separation between them

The surface of these had the ability to selectively absorb The surface of these had the ability to selectively absorb substances from the mediumsubstances from the medium

Even though they were non-living, they showed certain Even though they were non-living, they showed certain structural and functional properties of living organisms.structural and functional properties of living organisms.

Main steps in origin of life Main steps in origin of life according to Oparin theoryaccording to Oparin theory

Free atomsFree atoms - H, C, O and N- H, C, O and N↓↓

Inorganic moleculesInorganic molecules

++ - H- H22, H, H22O, CHO, CH44, NH, NH33, CO, CO22, HCN, HCN

Organic moleculesOrganic molecules↓↓

Simple organic compounds-Simple organic compounds- fatty acids, gylcerol, ADP fatty acids, gylcerol, ADP ↓↓amino acids, ATPamino acids, ATP

Complex organic compounds-Complex organic compounds- polysaccharides, fats, polysaccharides, fats,↓↓ proteins, nucleic acidsproteins, nucleic acids

CoacervatesCoacervates - colloidal droplets of organic - colloidal droplets of organic ↓↓ moleculesmolecules

Precells or Protobionts-Precells or Protobionts- the primitive life forms. the primitive life forms.

Microsphere theory of Sydney FoxMicrosphere theory of Sydney Fox

It was put forth by It was put forth by Dr.Sydney FoxDr.Sydney Fox in 1959. in 1959.In his experiment, he simulated the prebiotic In his experiment, he simulated the prebiotic conditions.conditions.He heated the amino acids which polymerized He heated the amino acids which polymerized into a protein like droplet known as into a protein like droplet known as protenoidsprotenoids..These protenoids aggregated into colloidal These protenoids aggregated into colloidal droplets known as droplets known as microspheresmicrospheres..These resembled the bacteria and were uniform These resembled the bacteria and were uniform in shape and size and were stable for a long in shape and size and were stable for a long period.period.The membrane of these had osmotic propertyThe membrane of these had osmotic propertySome of them had the capacity to multiply on Some of them had the capacity to multiply on their own by fission and fragmentationtheir own by fission and fragmentation

7. From pre cells to cells7. From pre cells to cells

Pre cells or protobionts gradually acquired Pre cells or protobionts gradually acquired other properties of life and got other properties of life and got differentiated into cells.differentiated into cells.

Nucleic acids also started to direct a series Nucleic acids also started to direct a series of chemical reactions including protein of chemical reactions including protein synthesis.synthesis.

First form of life originated after a long First form of life originated after a long process of molecular evolutionprocess of molecular evolution

Thus chemical evolution gave rise to Thus chemical evolution gave rise to biological evolutionbiological evolution

8. Initiation of Biological Evolution8. Initiation of Biological Evolution

The first primitive living organisms were The first primitive living organisms were heterotrophs which obtained energy by heterotrophs which obtained energy by fermentation of organic substancesfermentation of organic substances

Mutation acted upon these and formation Mutation acted upon these and formation of chlorophyll was the favourable change. of chlorophyll was the favourable change. These mutants became autotrophs.These mutants became autotrophs.

Then reducing environment gradually Then reducing environment gradually changed to oxidizing onechanged to oxidizing one

It lead to the formation of ozone layer and It lead to the formation of ozone layer and reduced UV rays reaching the earth which reduced UV rays reaching the earth which provided stability for the progressive forms provided stability for the progressive forms of lifeof life

Primitive earth

Atoms in free state

Inorganic molecules

Simple organic molecules

Macromolecules

Coacervates

Protocell

Anaerobic heterotrophs

Aerobic autotrophs

Stanley Millers ExperimentStanley Millers Experiment

Worked out by Worked out by Stanley L.MillerStanley L.Miller in the in the laboratory of laboratory of Harold Harold C. UreyC. Urey at the at the university of Chicagouniversity of Chicago

It is also known as It is also known as Urey-Miller Urey-Miller experiment or Spark experiment or Spark discharge experimentdischarge experiment

It is a simulation of It is a simulation of prebiotic conditions to prebiotic conditions to find out the possibility find out the possibility of getting organic of getting organic compounds compounds

Spark discharge apparatusSpark discharge apparatus

Methane, ammonia and Methane, ammonia and hydrogen in 1:2:2 ratiohydrogen in 1:2:2 ratio

Partially filled with water and Partially filled with water and heatedheated

Exposed to electrical Exposed to electrical discharge for several daysdischarge for several days

Passed through a condenser Passed through a condenser and the content was and the content was analyzedanalyzed

It showed the presence of It showed the presence of amino acids, hydrogen amino acids, hydrogen cyanide, fatty acid, urea, etc.cyanide, fatty acid, urea, etc.

IntroductionIntroduction

The term was coined by The term was coined by Herbert SpencerHerbert SpencerEvolution is defined as ‘ Evolution is defined as ‘ origin of new origin of new forms of life from pre existing life by forms of life from pre existing life by undergoing slow and gradual changesundergoing slow and gradual changes’’Gradual orderly change occurring in non-Gradual orderly change occurring in non-living world is known as inorganic living world is known as inorganic evolutionevolutionSuch a change in relation to plants and Such a change in relation to plants and animals is known as animals is known as organic evolutionorganic evolution

Theories of Organic EvolutionTheories of Organic Evolution

LamarckismLamarckism

Proposed by Baptiste Proposed by Baptiste de Lamarck in 1809de Lamarck in 1809

Published in his book Published in his book “ “ philosophic zoologique”philosophic zoologique”

““Use and disuseUse and disuse” and ” and ““inheritance of acquired inheritance of acquired characterscharacters””

Ex: Long neck in Ex: Long neck in GiraffesGiraffes

DarwinismDarwinism

Charles Robert Darwin-Charles Robert Darwin-

Father of EvolutionFather of Evolution

Born in Shrewsbury, England in Born in Shrewsbury, England in 18091809

Grandson of naturalist and Grandson of naturalist and physician Erasmus Darwinphysician Erasmus Darwin

Studied medicine at the Studied medicine at the University of EdinburghUniversity of Edinburgh

At 20, he became a naturalist At 20, he became a naturalist and traveled round the world in and traveled round the world in a ship called ‘a ship called ‘H.M.S.BeagleH.M.S.Beagle’.’.

During his voyage, he visited During his voyage, he visited Galapagos IslandGalapagos Island

In 1858, Darwin along with In 1858, Darwin along with Alfred Russel Wallace Alfred Russel Wallace presented their papers before presented their papers before Linnean Society in LondonLinnean Society in London

In 1859, they published their In 1859, they published their views in a book entitled views in a book entitled “ “ Origin of Species by Natural Origin of Species by Natural Selection”Selection”

It is regarded as It is regarded as ‘ Bible on ‘ Bible on evolution’evolution’

His theory is also known as His theory is also known as “ “ theory of natural selection’theory of natural selection’

Theory of Natural SelectionTheory of Natural SelectionHis theory mainly His theory mainly includes three includes three observations and two observations and two conclusionsconclusions

ObservationsObservationsProdigality of productionProdigality of production

Constancy of numberConstancy of number

Occurrence of variationsOccurrence of variations

ConclusionsConclusionsStruggle for existenceStruggle for existence

Survival of the fittestSurvival of the fittest

Prodigality of ProductionProdigality of ProductionThere is overproduction There is overproduction of organisms in geometric of organisms in geometric proportionproportion

Overproduction is the Overproduction is the tendency of all living tendency of all living organisms to multiply organisms to multiply rapidlyrapidly

The organisms produce The organisms produce more offsprings which are more offsprings which are more than necessary to more than necessary to replace themreplace them

Evening Primrose produces Evening Primrose produces 1,18,000 seeds 1,18,000 seeds A bacteria produces two A bacteria produces two individuals in 30 minutesindividuals in 30 minutesAn Elephant with an average An Elephant with an average life of 100 years produces six life of 100 years produces six offsprings. Such a rate if offsprings. Such a rate if continued, descendents of a continued, descendents of a single pair after 750 years single pair after 750 years would be about 19 millionwould be about 19 millionAn Oyster lays 50 million eggs An Oyster lays 50 million eggs in one season. If all these in one season. If all these survive and reproduce for 5 survive and reproduce for 5 generations, the volume generations, the volume occupied these will be eight occupied these will be eight times the size of earth.times the size of earth.

Constancy of numberConstancy of number

In nature, the population size remains In nature, the population size remains more or less constant or steady over the more or less constant or steady over the period of time.period of time.

It is determined by factors like food, It is determined by factors like food, shelter, light, etc.shelter, light, etc.

Population increases till the environment Population increases till the environment supports no further increasesupports no further increase

Occurrence of VariationsOccurrence of Variations

It is the difference in characters between the It is the difference in characters between the individuals of common descentindividuals of common descent

According to Darwin, ‘According to Darwin, ‘no two individuals are no two individuals are exactly alike’exactly alike’

Young ones of the same parents showed Young ones of the same parents showed variations with regard to size, colour, health, variations with regard to size, colour, health, strength and susceptibility to diseasesstrength and susceptibility to diseases

Variations can be continuous or discontinuous Variations can be continuous or discontinuous type and harmful or useful or neutral typetype and harmful or useful or neutral type

Useful variationsUseful variationsAdvantageous to the possessorAdvantageous to the possessor

Increases the chances of survivalIncreases the chances of survival

Development of disease resistance in Development of disease resistance in plantsplants

Harmful variationsHarmful variationsHinder the possessor during the Hinder the possessor during the struggle for survivalstruggle for survival

It may lead to the total elimination of It may lead to the total elimination of an individualan individual

Chlorophyll deficiency in plantsChlorophyll deficiency in plants

Neutral variationsNeutral variationsNeither help nor harm the possessorNeither help nor harm the possessor

Not significant from evolutionary point Not significant from evolutionary point of viewof view

Variations in leaf form, type of stem, Variations in leaf form, type of stem, shape of fruitshape of fruit

Environmental variationsEnvironmental variationsAcquired by the organisms due to the Acquired by the organisms due to the influence of environmentinfluence of environment

These are temporary and not heritableThese are temporary and not heritable

They have no role in evolutionThey have no role in evolution

Genetic variationsGenetic variations Variations in genetic make up of an individualVariations in genetic make up of an individual

These are permanent and heritableThese are permanent and heritable

Play an important role in evolutionPlay an important role in evolution

Struggle for ExistenceStruggle for Existence

The competition that the The competition that the organism has to face in organism has to face in order to surviveorder to survive

Competition for basic Competition for basic needs as well as avoid needs as well as avoid predation, parasitism and predation, parasitism and diseasesdiseases

Intraspecific struggleIntraspecific struggle

Interspecific struggleInterspecific struggle

Environmental struggleEnvironmental struggle

Survival of the FittestSurvival of the Fittest

Survival of the FittestSurvival of the Fittest

Organisms that possess favorable variations Organisms that possess favorable variations in the struggle for existence are called the in the struggle for existence are called the fittestfittest

It is quietly done by nature and too slight to It is quietly done by nature and too slight to be noticed (imperceptible)be noticed (imperceptible)

Organisms with unfavorable variations are Organisms with unfavorable variations are eventually reduced and become extincteventually reduced and become extinct

This kind of filtering mechanism or selection This kind of filtering mechanism or selection by nature is called natural selectionby nature is called natural selection

Origin of species by natural Origin of species by natural selectionselection

Selection of better adapted individuals with Selection of better adapted individuals with useful variations by natureuseful variations by nature

Organisms with favourable variations are Organisms with favourable variations are allowed to reproduce by natureallowed to reproduce by nature

More and more better adapted individuals More and more better adapted individuals are formed every generationare formed every generation

Leads to the formation of new speciesLeads to the formation of new species

Origin of new speciesOrigin of new species↑↑

Accumulation of positive variationsAccumulation of positive variations↑↑

Survival of the fittestSurvival of the fittest↑↑

Natural selectionNatural selection↑↑

Positive variationsPositive variations Elimination Elimination↑↑ ↑ ↑

Occurrence of variationsOccurrence of variations → Negative variations → Negative variations↑↑

Struggle for existenceStruggle for existence↑↑

Over productionOver production

Origin of Long necked Giraffe Origin of Long necked Giraffe on the basis of natural selectionon the basis of natural selection

Over productionOver production Short supply of basic Short supply of basic

needneed Favourable variationsFavourable variations Struggle for existenceStruggle for existence Nature selected Nature selected

longest necked oneslongest necked ones

Evidences from Peppered mothEvidences from Peppered moth

Biston betulariaBiston betularia

Peppered variety (light Peppered variety (light grey colored body and grey colored body and wings with pepper like wings with pepper like spots)spots)

B.betularia carbonariaB.betularia carbonaria, , melanic formmelanic form

Black body and wingsBlack body and wings

Nature selected peppered Nature selected peppered varietyvariety

Evidences form DDT resistance Evidences form DDT resistance in Mosquitoin Mosquito

Paul Miller invented Paul Miller invented DDT after II world warDDT after II world war

Survival of the fittestSurvival of the fittest Natural selectionNatural selection

Mutation theoryMutation theory

Put forth by Put forth by Hugo de Hugo de VriesVries in 1902 in 1902

Observations made on Observations made on ornamental plant ornamental plant Oenothera lamarckianaOenothera lamarckiana

Identified many mutants Identified many mutants which resulted in a new which resulted in a new approach to evolutionapproach to evolution

O.nanella, O.brevistylis,O.nanella, O.brevistylis,

O.laevifolia, O.gigasO.laevifolia, O.gigas

O.oblongata, O.albidaO.oblongata, O.albida

Progressive speciesProgressive speciesProvided with new characters not seen in parents and Provided with new characters not seen in parents and are better adaptedare better adapted

Ex: Ex: O.gigasO.gigas

Retrogressive speciesRetrogressive speciesShowed loss of some parental charactersShowed loss of some parental characters

Ex: Ex: O.brevistylisO.brevistylis

Degressive speciesDegressive speciesShowed the loss of vital charactersShowed the loss of vital characters

Ex: Ex: O.albida, O.oblongataO.albida, O.oblongata

Inconstant speciesInconstant speciesDo not breed true and often produce new varietiesDo not breed true and often produce new varieties

Ex: Ex: O.scintillansO.scintillans

Salient features of mutation theorySalient features of mutation theory

Mutations are spontaneous and heritableMutations are spontaneous and heritableRaw materials for evolutionRaw materials for evolutionThey are sudden quick jerky processThey are sudden quick jerky processNo intermediate stagesNo intermediate stagesMay be progressive or retrogressiveMay be progressive or retrogressiveSubjected to natural selectionSubjected to natural selection

Evidences for mutationEvidences for mutation

Short bow legged Short bow legged sheep Ancon sheep Ancon

Lack of pigmentation Lack of pigmentation or albinism in or albinism in organismsorganisms

NeodarwinismNeodarwinism

Put forth by Huxley, Put forth by Huxley, Haldane, Dobzhansky, Haldane, Dobzhansky, Goldsmith, Fischer, Goldsmith, Fischer, Muller, etc.Muller, etc.Modern synthetic theory, Modern synthetic theory, Modern Evolution theoryModern Evolution theoryThe constructors of this The constructors of this theory are known as theory are known as NeodarwiniansNeodarwiniansCombination of Combination of Darwinism, Mendelism Darwinism, Mendelism and views of Hugo De and views of Hugo De Vries theoryVries theory

Dobzhansky

Neodarwinian conceptNeodarwinian concept

Change in gene frequency is evolutionChange in gene frequency is evolutionSomatic and germinal variations were Somatic and germinal variations were

differentiateddifferentiatedEvolution operates on gene poolEvolution operates on gene poolEvolution operates through differential Evolution operates through differential

reproduction and comparative reproduction and comparative reproductive successreproductive success

It explains the arrival of the fittestIt explains the arrival of the fittest

Gene poolGene pool

It is defined as It is defined as ‘ the sum total of all the genes ‘ the sum total of all the genes present in a large sexually reproducing present in a large sexually reproducing populationpopulation’.’.It represents all the genes of all individuals put It represents all the genes of all individuals put together in a given populationtogether in a given populationIt is not static It is not static Consistently changing gene pool undergoes Consistently changing gene pool undergoes evolutionary changesevolutionary changesIf it is more or less static, it fails to bring about If it is more or less static, it fails to bring about evolutionary changesevolutionary changes

Gene frequencyGene frequency It is defined as ‘ the ratio of different alleles of a gene in a It is defined as ‘ the ratio of different alleles of a gene in a

population’.population’. Ex: Coloration in human population controlled by two alleles Ex: Coloration in human population controlled by two alleles

A (dominant) and a (recessive)A (dominant) and a (recessive) Possible genotypes: AA, Aa, aaPossible genotypes: AA, Aa, aa Consider a population of 100 individuals with 40 AA, 40 Aa Consider a population of 100 individuals with 40 AA, 40 Aa

and 20 aaand 20 aa Total number of A gene- 40x2 (AA)+40(Aa)=100Total number of A gene- 40x2 (AA)+40(Aa)=100 Total number of a gene- 40x2(AA)+40(Aa)=100Total number of a gene- 40x2(AA)+40(Aa)=100 Total number of alleles= AA + Aa + aaTotal number of alleles= AA + Aa + aa

40x2 40+40 20x2= 20040x2 40+40 20x2= 200frequency of A is 80+40=120/200=0.6frequency of A is 80+40=120/200=0.6frequency of a is 20+40=80/200=0.4frequency of a is 20+40=80/200=0.4

Gene frequency is A:a 0.6:0.4Gene frequency is A:a 0.6:0.4

Hardy-Weinberg LawHardy-Weinberg Law

Proposed by Proposed by G.H.HardyG.H.Hardy and and E.Weinberg E.Weinberg in 1908.in 1908.

Establishes a connection between Establishes a connection between evolution and gene frequenciesevolution and gene frequencies

Law is defined as ‘ Law is defined as ‘ in a large population, in a large population, the gene frequencies of various kinds of the gene frequencies of various kinds of genes remain constant, generation after genes remain constant, generation after generation under certain conditionsgeneration under certain conditions’.’.

Conditions responsible for Hardy-Conditions responsible for Hardy-Weinberg equilibriumWeinberg equilibrium

It operates only on a large sexually reproducing It operates only on a large sexually reproducing populationpopulationAllele frequencies of male and female should be Allele frequencies of male and female should be samesameAllele genotypes must be equally viable and Allele genotypes must be equally viable and fertilefertileMutations, migrations and selection should not Mutations, migrations and selection should not occuroccurEvolution occurs only when the equilibrium is Evolution occurs only when the equilibrium is alteredalteredLaw is represented as p+q=1Law is represented as p+q=1

ExampleExampleConsider two alleles M and m with genotypes Consider two alleles M and m with genotypes MM, Ma and mmMM, Ma and mm

Represent gene frequency of M as p and m as q.Represent gene frequency of M as p and m as q.According to law, p+q=1According to law, p+q=1Relationship between gene and gene frequency Relationship between gene and gene frequency

is (p+q)is (p+q)22=p=p22+2pq+q+2pq+q22

If gene frequency M and m is 50%If gene frequency M and m is 50%then, p=50%=1/2=0.5then, p=50%=1/2=0.5

q=50%=1/2=0.5q=50%=1/2=0.5Genotype frequency is (p+q)Genotype frequency is (p+q)22=p=p22+2pq+q+2pq+q22

=(0.5)=(0.5)22+2(0.5)(0.5)+(0.5)+2(0.5)(0.5)+(0.5)22=1=1It can be expressed as 25%pIt can be expressed as 25%p22+50%pq+25%q+50%pq+25%q22

25%MM+50%Mm+25%mm=100%25%MM+50%Mm+25%mm=100%

Sources of variationsSources of variations

Variations

Sexual reproduction

Gene flowIsolation

Mutation Genetic drift

1. Sexual Reproduction1. Sexual Reproduction

It is a physiological process through which It is a physiological process through which an organism produces young ones of its an organism produces young ones of its own kind to continue the raceown kind to continue the race

Asexual reproduction does not contribute Asexual reproduction does not contribute to evolutionto evolution

Sexual reproduction involves Sexual reproduction involves gametogenesisgametogenesis and and fertilizationfertilization

ParentsParents AaBbAaBb xx AaBbAaBb

GametesGametes AB Ab aB ab AB Ab aB ab

♀♂

AB Ab aB ab

AB AABB AABb AaBB AaBb

Ab AABb AAbb AaBb Aabb

aB AaBB AaBb aaBB aaBb

ab AaBb Aabb aaBb aabb

2. Gene flow2. Gene flow

It is defined as ‘It is defined as ‘transfer of genes between transfer of genes between two inter breeding populations which differ two inter breeding populations which differ geneticallygenetically’’

It leads to increased genetic variations and It leads to increased genetic variations and evolutionary changes.evolutionary changes.

It is brought about by migration and It is brought about by migration and hybridizationhybridization

3. Genetic drift3. Genetic drift It is the random changes in gene frequency in a It is the random changes in gene frequency in a

small population, purely by chance.small population, purely by chance. It is also known as It is also known as ‘Sewall Wright effect’‘Sewall Wright effect’ FeaturesFeatures

It operates on small populationIt operates on small population

It is purely by chanceIt is purely by chance

Genes may be totally lost, reduced or increasedGenes may be totally lost, reduced or increased

Heterozygous gene pairs become homozygous by Heterozygous gene pairs become homozygous by chance factorchance factor

Fixes or eliminates any trait irrespective of its adaptive Fixes or eliminates any trait irrespective of its adaptive valuevalue

Alters Hardy-Weinberg law and helps in origin of a new Alters Hardy-Weinberg law and helps in origin of a new speciesspecies

4. Mutation4. Mutation

It is defined as ‘It is defined as ‘a spontaneous, permanent a spontaneous, permanent change in the genetic make up of an change in the genetic make up of an individual’.individual’.

Gene mutationGene mutation Ex: Replacement of glutamine by valine in Ex: Replacement of glutamine by valine in

Haemoglobin results in Sickle Cell anaemiaHaemoglobin results in Sickle Cell anaemiaChromosomal mutationChromosomal mutation

Turner’s syndromeTurner’s syndromeKlinefelter’s syndromeKlinefelter’s syndrome

5. Isolation5. Isolation

It is defined as ‘ It is defined as ‘ separation of a population separation of a population into sub units, by some barriers which into sub units, by some barriers which prevents interbreedingprevents interbreeding’’

Each isolated group is acted upon by Each isolated group is acted upon by evolutionary forces which results in the evolutionary forces which results in the formation of a new speciesformation of a new species

TypesTypesGeographical isolationGeographical isolationBehavioural isolationBehavioural isolationMechanical isolationMechanical isolationGenetic isolationGenetic isolation

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