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Origin And Evolution Of Life


Philosophers and scientists have been busy to solve the riddle as to how the universe and our earth were formed and how and when 'life' originated on earth. The branch of life science for the study of 'Origin of life' and evolution of different forms of life on earth was called Bioevolution or Evolutionary Biology by Mayer,(1970).

The study of universe or cosmos is called Cosmology. Our earth belongs to the Solar system having nine stars called planets constantly rotating around a common Sun. On the basis of the order of the distance from the sun these planets include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto while moon is a satellite of earth. The universe is made up of matter and energy and it was formed about 10 to 13 billion years ago as a red hot, dense, rotating gaseous cloud of cosmic dust called Ylem or primaeval matter. The Ylem consisted of particles of matter (like neutron, proton and electron) and antiparticles of antimatter. Scientists like Lemaitre(1931), Gamow(1948), Dicke(1964) etc. supported the Big-Bang Hypothesiswhich explains that collision between these particles and antiparticles caused a tremendous explosion to form atoms of hydrogen.

  • Life is expression of metabolism.

  • Sodium chloride forms about 0.9%of blood of mammals including man.

  • Sodium chloride forms about 0.7% of blood of frog.

  • Glucose forms about 0.1%of body weight. Normal glucose level is 60-100 mg/100 dlof blood.

  • Transformation of excess of glucose into glycogen is called glycogenesis,while breakdown of glycogen into glucose is called glycogenolysis.

  • Intussusceptional growth: Internal growth found in living organisms.

  • Accretional growth: External growth found in non-living objects e.g. CuSO4crystals.

  • Biosphere:Also called Ecosphere or Giant ecosystem or life supporting system of earth.

  • Linus Paulingstated: Life is the result of relationship of molecules and is not a property of any one molecule.

  • Glycogen :Also called animal starch.

  • ATPwas first discovered by Karl Lohmanin skeletal flight muscles of insects.

  • Agar: A homopolysaccharide of fructose, so is also called fructan.

  • Physiological fuel value of 1gm of glucose = 4.0 Kcal (17 K.joules).

  • Physiological fuel value of 1gm of Fat = 9.0 Kcal (37 K.joules).

  • RNA: Genetic material in certain viruses (e.g. HIV, TMV); help in protein synthesis.

  • A phospholipidis formed of one unit of glycerol, two units of fatty acids attached at - and -carbon of glycerol, and a unit of phosphate at the other end of glycerol which, in turn, is linked to a nitrogen base (e.g. ethanolamine in cephalinand choline in lecithin).

  • A phospholipid is an amphipathic or bipolar moleculebecause its fatty acids (tails) represent the hydrophobic ornon-polar end while its phosphate-containing end is hydrophilicor polar end.

  • Prostglandinsare modified fatty acids and first reported in the secretions of prostate gland.

  • There are 3,000 different types of proteins in Escherichia colibacterium, and about 100,000 different types of proteins in the human being.

  • TSH-RF : Smallest known proteinand is formed of only 3 amino acids.

  • Angiotensin-II and Vasopressin or ADHare proteins formed of 8 and 9 amino acids respectively.

  • Largest known polypeptide in human beings is procollagenand is formed of 1200 amino acids.

  • Every second, about 10 million molecules of ATP are formed from ADP and phosphate molecules and equal number of ATP molecules are hydrolyzed to provide energy for metabolic processes.

  • Bioenergetics: Branch of science dealing with energy kinetics-, in living systems.

  • Phillipson: Gave the term bioenergetics.

  • Second law of thermodynamicsis also called law of Entropy.

  • Rudolf Clausius :Gave the term entropy.

  • No energy transfer or transformation is cent percent efficient.

  • An open system is only a part of a larger closed system.

  • Entropy is maximum at the time of death.

  • Walter B.Cannon : Gave the term homeostasis(also called physiological equilibrium)

  • Homeostasis also operates at all levels of ecological hierarchy (e.g. population, community, ecosystem and biosphere) and helps in keeping an ecological balance.

  • Glucose deficiency first of all affects the neurons of CNS.

  • Autotrophs are called self-feeders,while heterotrophs are called other feeders.

  • Homeostasis operates in many organs of body like brain, kidney, liver, skin, etc. Homeostasis is found in all the living organisms. Main centres of maintaining homeostasis are hypothalamus and medulla oblongata.

  • Majority of plant viruses have RNA (e.g. TMV) but Cauliflower mosaic virus is with DNA.

  • Life originated in the Precambrian period.

  • The nature of primitive earth was reducing and that of atmosphere was oxidizing.

  • Theory of Eternity was proposed by Preyer in 1880.

  • Cuvier proposed the theory of Catastrophism.

  • Cosmozoic theory was proposed by Richter in 1865.

  • Arrhenius in 1908 proposed the theory of Panspermea or Interplanetary theory.

  • The theory of Biochemical origin of the life was proposed by Oparin in 1923 and supported by Haldane in 1928.

  • Very and Millesion 1953 performed an experiment to demonstrate that life originated from a hot cup of soup.

  • Coacervates as pre-cells were formed due to aggregation of organic molecules.

  • Protocells evolved into first true cells.

  • Eukaryotes developed around 1600 million years ago.

  • Giovanne Avaduina (1760) gave the first geological time scale.

  • Archaeopteryx lithegraphicais a connecting link between reptiles and birds.

  • Intermediate forms between two groups and show the possible path of evolution are known as connecting links.

  • Biogenetic law or Recapitulation theory was proposed by Hacekel in 1868.

  • Lamarck in 1801 proposed that organisms undergo changes to adapt themselves to the environment and the characters thus acquired are passed on to the next generation.

  • Charles Darwin in 1809 proposed the theory of natural selection.

  • The sum total of all the genes present in the population termed as gene pool.

  • In 1902 Hugo de Vries proposed the Mutation theory.

  • The random changes in gene frequencies occurring by chance and not under the control of natural selection are called genetic drift.

  • The phenomenon of formation of new species from pre-existing ones is called speciation.

  • T.H. Huxley, 1863 first tried to explain evolution of humans.

  • Oxygen was absent in the atmosphere at the time of origin of life. Condition of atmosphere was anaerobic.

  • Biogenesis states life originated from pre-existing life (omanis cellula e cellula).

  • First organisms were blue-green algae (cyanobacteria developed near sea shore).

  • First sign of life was coacervates (nucleoprotein).

  • Cyanobacteria converted the reducing nature of earth to oxidizing (aerobic).

  • In azoic era life was absent. Prokaryotes / Monera originated in the Archeozoic era.

  • Eukaryotes, green algae and primitive invertebrates developed during Precambrain / Proterozoic era.

  • Trilobites appeased in cambrain period.

  • Land plants first appeared in Ordovician (420-500 million years) and silurian (400-420 million years) periods.

  • Coal formation took place in the carboniferous period.

  • Mammals originated in the Triassic period of Mesozoic era.

  • Dinosaurs and cycads originated in the Jurassic period.

                             Difference between Lamarckism and Neo–Lamarckism



It is original theory by Lamarck.

The theory lays stress on internal force, appetency and use and disuse of organs.

It believes that changes in environment brings about a conscious reaction in animals.

According to Lamarckism the acquired characters passes on to the next generation.

It is a modification of the original theory of Lamarck in order to make it more suitable to modern knowledge.

Neo–Lamarckism does not give any importance to these factors.

The theory stresses on the direct effect of changed environment on the organisms.

Normally only those modification are transferred to next generation which influence germ cells or where somatic cells give rise to germ cells.

                                                    Difference between Darwinism and Neo–Darwinism

Darwinism (Natural Selection)


  1. It is the original theory given by Charles Darwin (1859) to explain the origin of new species.

  2. According to this theory accumulation of continuous variations causes changes in individuals to form new species.

  3. It believes in the selection of individuals on the basis of accumulation of variation.

  4. Darwinism does not believe in isolation.

  1. It can explain the origin of new characters.

  1. Darwinism cannot explain the persistence of certain forms in the unchanged condition.

  1. Neo–Darwin is a modification of the original theory of Darwin to remove its short–comings.

  2. Instead of continuos variations, mutations are believed to help form new species.

  1. Variations accumulate in the gene pool and not in the individuals.

  2. Neo–Darwinism incorporates isolation as an essential component of evolution.

  3. The theory can explain the occurrence of unchanged forms over millions of years.

  4. Normally only those modification are transferred to next generation which influence germ cells or where somatic cells give rise to germ cells.

                                            Difference Amongst Lamarckism, Darwinism and Mutation Theory




Mutation Theory

1. Vital force

The theory believes that every organism has an internal vital force that tends to increase its size upto a certain limit.

Darwinism does not believe in internal vital force.

No internal vital force is involved.

2. Conscious Reaction

Animals with well developed nervous system react consciously  to any change in environments

Darwinism does not involve any conscious reaction.

No conscious reaction is believed to take part in the process of evolution.

3. Appentency

The theory considers appentency or desires on the part of animals an important force in the development of modifications.

It is not a constituent of the theory.

Appentency in not involved.

4. Use and Disuse

The organs put to more use are believed to develop more while organs not used begin to degenerate.

The theory is silent about use and disuse of organs.

The theory is silent about it.

5. Inheritance of  Acquired Characters

The characters acquired by an organism during its life are believed to get transferred the next generation.

According to Darwin, all the living cells produce minute particles or pangenesis, which pass into germ cells for transmission to the offspring.

Only those variations are transferred to the offspring which originate in germ cells or in the cells which form germ cells.

6.Struggle for Existence

The theory does not clearly spell out struggle for existence in relation to high biotic potential.

Organisms produce more offspring than the available food and space so that a struggle for existence ensues amongst them.

The theory believes in the struggle for existence.

7. Origin of Variations

Variations appear in organisms in response to change in environment, conscious reaction, desire ruse and disuse of organs.

Variations appear automatically.

Variations appear due to change in genetic make up.

8.Continuous Variations

The theory is silent about them though it believes in a continuous modification of organs in a particular direction.

It is based on the origin and selection of continuous variations.

The theory is based on discontinuous variations or mutations.

9. Natural


The theory does not take into account natural selection or survival of the fittest.

Darwinism is based on natural selection or survival of the fittest.

Mutations theory believes in natural selection or survival of the fittest.

10.Progress of Evolution

Evolution is a continuous process which moves in a direction governed by environment and appentency.

Evolution is a continuous process, the direction of which is governed by nature.

Evolution is a jerky process, the direction of which is unpredictable though ultimately it is governed by nature.


Note:According to A.S. Romer different human races can be divided mainly into four groups.

(a) Australoids :It is the most primitive and simple existing human race. Bushmenof Australia and Africa, Bhilsof India and Veddansof Srilanka are included in this group. They have dark skin, elongated skull, flat nose, small forehead, eye brow ridges prominent, thick body hair and hair on head.

(b) Negroids :Negroes of Africa and Pacific islands and Pygmies of Congo, Andman, Malaya, Newguinea and Philippines are included in this race. They live in tropical regions. Their colour of skin is black, head is long and broad, forehead is high, nose flattened, lips are thick and hair on head are wooly.

(c) Caucasoids :These inhabit in temperate regions like countries around Mediterranian sea including North Africa, Europe, Russia, Arab countries and India. They have fair or brown coloured skin, long or broard head, thin nose and wavy hair on head. This race is often aggressive and dominant in nature.

(d) Mongoloids :Members of this group often inhabit colder regions of the world and include Chinese,Japanese, Mangols, Eskimos and Red Indians. Colour of skin is red, light brown or yellow. Body hair are sparse but hair on head are very thick straight, hard and black. Head is broad, cheek bones are high, nose medium in size and eyes are small. However, some anthropologists divide the present man into 6 human races.

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