Introduction -

Evolutionary biology –

The study of life forms on earth is known as evolutionary biology.

  • The process of gradual modification of simpler forms into the present complex forms over millions of years is called evolution.

Origin Of Universe

  • The universe is almost 20 billion years old.
  • Huge clusters of galaxies comprise the universe.
  • Galaxies contain stars and clouds of gas and dust.
  • A scientific theory called big bang theory explains that, the unimaginable large explosion created the universe.
  • As the universe expanded and cooled, the temperature came down and materials condensed under the influence of gravitation to form present day galaxy.

Big Bang Theory

According to it a huge , explosion occurred , the universe expanded , temperature came down and hydrogen and helium were formed later. The galaxies then were formed due to condensation of gases under gravitation.


    • Our galaxy is called milky way formed 4.5 billion years back.
    • There was no atmosphere on early earth.
    • Water vapour, methane, carbon dioxide and ammonia released from molten mass covered the surface.
    • The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2.
    • Oxygen combined with ammonia and methane to form water co2 and others.
    • The ozone layer was formed, as it cooled, the water vapor fell as rain, fill all the depressions and form oceans.


    • 1. Life appeared 500 million years after the formation of earth, i.e, almost billion years back.
    • 2. Different scientists had put different views about the origin of life.
    • 3. THOERY OF SPECIAL CREATION:- According to this theory god created life by his divine act of creation.
    • 4. THOERY OF PANSPERMIA /COSMOZOIC THEORY :- According to early greek thinkers, unit of life called spores or panspermia came from outer space and developed into living forms.
    • 5. THOERY OF SPONTANEOUS GENERATION:- According to this theory , life originated from decaying and rotting matters like straw , mud etc.
    • NOTE 

      • Louis pasteur dismissed the theory of spontaneous generation and demonstrated that life came from pre existing life.
      • He placed killed yeast in pre-sterilized flask and another flask open to air . he showed that life did not originate in the former but new living organisms arose in the latter flask.
    • Theory Of Chemical Evolution Or Oparin Haldane Theory
    • This theory was given by oparin and haldane and stated that life originated from pre existing non living organize molecule (eg:- RNA, Protein etc)

      The conditions on earth favouring chemical evolution were high temperature, volcanic storms, reducing atmosphere containing CH3 etc.

Experimental evidence of chemical evolution miller’s experiment.

    • 1. In 1953 , Stanley miller and harold urey tested the oparin-haldane hypothesis using the condition of pre-biotic earth.
    • 2. Experimental set up- in a closed flask containing CH3, H2, NH3 and water vapor at 800’ c.
    • 3. Electrical discharge was created.
    • 4. The condition were similar to those in primitive atmosphere.


        1. It provides experimental evidence for the theory of chemical origin.
        2. It shower that the first non- cellular biomolecules exist in the form of DNA, RNS, Polysaccharides. And protein.

          After a week they observations presence of amino acid complex molecules like sugars nitrogen pigments and fats in the flask.


          Formation of first cell-

          • First non- cellular life forms originated 3 millions years ago.
          • These could be giant molecules like RNA,protein and Polysaccharides. And protein.
          • First cellular form of life originated about 2000 million year ago.
          • These might have been single cell formed in aquatic environment.

Evidences For Evolution

Paleontological evidences

  • Palaeontology-  the study of fossils is called palaeontology.
  • Fossils – are the remains or impression of past organism preserved in sedimentary rocks or other media.
  • Different aged rock sediment in earth’s crust indicate the presence of fossils of different life forms which died during the sediment formation.
  • A variety of fossils ranging from the modern organism to extinct organism sedimentary.
  • By studying the different sedimentary layers the  geographical time period in which the organism existen be predicted.


  • Palaeontologists view archaeopteryx as a transitional fossil between dinosaurs and modern birds. With its blend of avian and reptilian features, it was long viewed as the earliest known bird. Discovered in 1860 in germany.

  • Archaeopteryx lived around 150 million years ago- during the early tithonian stage in the late jurassic period.

Vestigial organs :-

Vestigial organs are the useless body parts, which do not perform any functions in the body and are present as reduced structures. These organisms are functional in many lower organisms ; therefore, these organs can be considered an evidence for evolution

  • Examples include Ear muscles, tailbone, male nipples, wisdom teeth, etc.

         The human vermiform appendix is another example

Age of fossils is determined by the process called.

Morphological and comparative anatomical evidence.

Phylogeny – 

The study of ancestor is called phylogeny.

1. The phylogenetic history can be revealed by comparative study of external and internal structures.

2. Comparative anatomy and morphology shows similarities and differences among organisms of today and those that exited years ago.

  • Homologous organs

  • Analogous organs

Homologous organs –

  • The organs whose structure or origin is same but functionally different.

Example – vertebrate hearts or brains, in plants, the thorns and tendrils of bougainvillaea and cucurbita, the forelimbs of whale, bats, cat and human share similarities in the pattern of forelimb bones.

  • All the animals have similar anatomical structure in their forelimb bones such as humerus, radius, ulna, carpals metacarpals and phalanges.
  • Though the forelimbs have similar anatomical structure but they perform different functions.
  • The same structure developed along different directions due to adaptations to different needs.
  • Homology is based on divergent evolution.
  • Homology indicates common ancestry.

Divergent evolution

Due to different needs, some structures developed differently. This is called divergent evolution.

Analogous organs

The organs which are anatomically different but functionally similar are called analogous organs 

For example- wings of butterfly and birds.

Other example include

  1. Eye of octopus and mammals
  2. Phyllodes and leaves
  3. Butterfly wings and bat wings

Due to sacde function different structures evolve similarly , this is called

Convergent evolution

Sweet potato (root modification) and potato ( stem modification)

Biochemical evidence 

The similarities in proteins and genes performing a common given function among diverse organism given clues to common ancestry

The most convincing evidence of descent from a common ancestor comes from the similarities in the biochemical composition and physiological activities of organisms.

  1. Enzymes and hormones: in the same manner similar or identical enzymes and hormones, are found in large number of animals groups. For example, trypsin- the  protein splitting enzyme, is found in animals from protozoa auto mammals and amylase from sponges to man.
  2. chromosomes :the essential component of nucleus in every living cell is the chromosomes. The chemical composition of DNA is basically the same in all living beings except for differences in the sequence of nitrogenous bases.
  3. Genetic code: it is surprising to note that the same genetic code having triplet code is found from viruses to man.
  4. All of these organisms store energy in the form of ATP.

All the these factors of biochemistry provide evidence for evolution.

Biogeographical evidences

  • Species restricted to a region develop unique features.

  • Also species present in widely separated region show similarity of ancestry.

Adaptive radiation

Adaptive radiation is the relatively fast relatively fast evolution of evolution of many species from a single common ancestor. Adaptive radiation generally occurs when an organism enters a new area and different traits affect its survival. An example of adaptive radiation is the development of mammals after the extinction of dinosaurs.

  1. Darwin’s finches :- 

  • Darwin observed many varieties of finches in the same island.

  • All varieties had evolved from original seed – eating finches.

  • With alteration in beaks some became insectivorous and some vegetarian.

Marsupials of Australia

Within the australian continent, many different marsupials or pouched animals are seen.

These have evolved from a common ancestral stock.

Placental Animals in Australia 

A variety of placental mammals have evolved from the Australian with respect to their need.

Objectives :-

  1. Theories of evolution 
  2. Lamarck’s theory of evolution 
  1. Darwinian theory of evolution
  • Industrial melanism 
  • Chemical resistance
  • Mutation theory of evolution

Theory of evolution ( Biological Evolution)


Lamarck’s theory of evolution or lamarckism :-

According to lamarck’s evolution of life forms occurred due to use and disuse of organs.

Example:- Giraffes initially did not have a long necks. But to access leaves on tall trees,         

They had to adapt by elongating their necks. By passing this acquired character to succeeding generation, they acquired long necks,

This theory is more accepted

Darwinian Theory of Evolution :-

Charles darwin based on his observation during a sea voyage around the world in the ship H.M.S.beagle, concluded the following :-

Varying degree of similarities can be observed between existing life forms and those that existed million years ago.

Any population has built in variation in characteristics which adopt it better to environment.


Survival of the fittest:-

The characteristics which enable some populations or individuals to survive better in natural conditions ( climate, food, physical factors ).

Natural selection :-

Those populations which are better fit in an environment will be selected by nature and will survive more.

Natural selection is based on following factual observations :- 

  1. Limited natural resources
  2. Stable population size except seasonal fluctuations.
  3. Varying character of member of population.
  4. Most of variations are inherited.

The two key concept of darwinian theory are :-

Branching descent ( adaptive radiation ) and natural selection.


Industrial melanism :-

In England, before industrialization, white winged moths were more in number than dark winged moths.

But after industrialization,dark winged both became more in number than white winged moths.

This is because during industrialization, the tree trunks covered by white, lichens became dark due to deposition of dust and coal particles.

As a result, white winged moths could be easily picked up by predators from the dark background and dark winged moths survived.


Chemical resistance :-

  • Excessive use of herbicides and pesticides has resulted in evolution of resistant varieties of microbes in much lesser time scale.
  • As a result pathogenic bacteria are appearing is very short period.

Mutation theory of evolution.

  • Hugo de vries based on his work on evening primrose :-
  • According to him , evolution is caused by sudden large different in population i,e, mutation and not the minor variations as per drawing.
  • He believed that mutation caused speciation and called it saltation or single step large mutilation.
  • Mutations are random and directionless in corporate to small directional variations as per darwin.

Hardy weinberg princlple :-

This principle states that allelic frequencies in a population are stable and remain constand from generation to generation i, e, gwnw pool ( total number of genes and their alleles in a population ) is constand. This is called entic equilibrium or hardy- weinberg equilibrium.

hence , the formula is p2 + 2pq + q2 which binomial expansion of (p+q)2 which can be applied to any population to find out the gene frequency.

Factors affecting hardy- Weinberg principle are–

Gene flow –

  • The transfer of section of population to another place resulting in a change in gene frequencies in both old and new population is called gene flow.
  • New genes and alleles are added to new population which genetically different but can interbreed.

Genetic drift –

  • The random change in gene frequency occurs by chance is called genetic drift.
  • Sometimes,the change in allelic frequency is so different in the new population, that they become a different species and the original drifted population becomes founders hence the effect is called founder effect.


  • The spontaneous change in the genetic makeup of an individual is called mutation.
  • Pre-existing advantageous mutations when selected will result in observation of new phenotypes and over few generations this would result in 

Genetic recombination –

  • Exchange of genes between non sister chromatids of homologous chromosomes during gametogenesis is called genetic.
  • Variation due to recombination during gametogenesis,or due to gene, flow or genetic drift results in changes frequency of genes and alleles in future generation.

Natural selection –

  • The process by which better adapted individuals with useful variations are selected by nature and leave greater number of progenies is called natural selection.
  • Natural selection can lead to-
  • Stabilizing selection – here, more individuals acquire mean character value.
  • Directional change –  here, more individuals acquire other than the mean character value.
  • Disruptive selection – here, more individuals acquire peripheral character value at both ends of the distribution curve.

A Brief Account Of Evolution

  • About 2000 million years ago (mya) the first cellular forms of life appeared on earth.
  • Some cellular form had the ability to release o2 and slowly single cell organisms became multicellular organisms.

Evolution of Animals 

  • By the time of 500 mya, invertebrates were formed and active.
  • Jawless fish probably evolved around 350 mya . fish with stout and strong fins could move on land and go back to water.
  • In 1938, a lobe finned fish caught in south africa happened to be a coelacanth which evolved into first amphibians that lived on both land and water and water and these were the ancestors of modern day frogs and salamanders.
  • The amphibians evolved into reptiles which lay thick shelled eggs which do not dry up on earth.
  • The modern day descendants of reptiles are the turtles tortoises and crocodiles.
  • In the next 200 million years or so, reptiles of different shapes and sizes dominated on earth.
  • Some of the reptiles went back into water to evolve into fish like reptiles around 200 mya.
  • The land reptiles were the dinosaurs and the biggest of them is tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth.
  • About 65 mya, the dinosaurs suddenly disappeared from the earth, some of them evolved into birds or might be killed by the climatic changes.
  • The first mammals were like shrews and their fossils were small sized.
  • Mammals were viviparous and protected their unborn young inside the mother’s body.
  • Mammals dominated the earth when the population of reptiles came down.

Evolution of plants:-

  • Plants invaded land before animals.
  • Bryophytes originated earlier than vascular plants like pteridophytes and gymnosperm.
  • The first vascular plants developed in silurian period.
  • Sea weeds and few plants exited around 320 million years ago ( mya)







Origin And evolution of man :-

Origin And evolution of man :-

Dryopithecus and Ramapithecus –

  • About 15 mya. Primates called dryopithecus and ramapithecus were existing.
  • They were hairy and walked like gorillas and chimpanzees.
  • Ramapithecus was more man-like while dryopithecus was more ape-like.
  • Few fossils of ma-like bones have been discovered in ethiopia and tanzania.
  • These revealed hominid features leading to the belief that about 3-4 mya, man-like primates walked in eastern africa.



  • About two mya, australopithecines probably lived in east african grasslands.
  • They hunted with stone weapons but essentially ate fruit.
  • Some of the bones among the bones discovered were different.
  • They were intermediate between apes and man.

Homo habilis :-

  • The brain capacities were between 650-800 cc.
  • They probably did not eat meat.
  • They were the makers of stone tools.

Homo erectus- 

  • About 1.5 mya, homo erectus arose.
  • Homo erectus had a large brain around 900cc.
  • Homo erectus probably ate meat.

Neanderthal man-

  • The neanderthal man with a brain size of 1400cc lived in near east and central Asia between 1,00,000-40,000 years back.
  • They used hides to protect their body and buried their dead.

Homo sapiens or modern man –

  • Arose in africa and moved across continents.
  • During ice age between 75,000- 10,000 years ago modern homo sapiens arose.
  • Prehistoric cave art developed about 18,000 years ago.