Life is a unique, complex organization of molecules, expressing it through chemical reactions which lead to growth, development, response, adaptation, reproduction etc.
When we study the plants and animals, the first question arises in our mind i.e. how did they originate and later give rise to diversified plants and animals?

Different views have been put forward by different workers of different ages concerning the origin of life on the earth. They are described below:

1. Theory of special creation
· Spiritual theory
· Life was created by some supernatural power of God.
· According to Hindu mythology, Lord Brahma, the God of creation, created the world with his wish. The first man was Manu and the first woman was Shradha.
· According to Christian belief, God created the world and all living beings in six natural days. Earth and heaven were created on the first day, sky on the second day, plants on the third day, sun, moon and stars on the fourth day, fish and birds on the fifth day and animals on the sixth day.
· The greatest supporter of this theory was Spanish Priest Father Suarez.
· The three important postulates of the theory of special creation are as follows.
a) All the different kinds of life were created at once without any relationship with each other.
b) They did not undergo any change since their creation.
c) Their bodies and organs had been specially designed to meet fully the needs of the environment in which they had been created.

2. Theory of Spontaneous Generation (Abiogenesis or Autogenesis or Autobiogenesis)
· The process of origin of living beings from non-living materials in a spontaneous manner is called Abiogenesis.
· Concept further held by Thales, Anaximenes, Xenophanes, Empedocles, Plato and Aristotle.
· Anaximander (611-547 BC) thought life to be originated from the mud warmed by the sun.
· Anaximenes proposed that air is the sole cause of life.
· In ancient Egypt, it was believed that frogs, snakes and crocodiles could form from the mud of the river Nile.
· It was believed that a hair from the tail of a white horse when dropped into the water would change into a living horse hairworm (Gordius).
· Fly larvae were believed to be developed from rotten meat.
· Aristotle (384-322 BC) believed that insects were developed from morning dew and rotting manure, tapeworms from the excreta of animals and crabs, salamanders from wet earth and slime.
· From ancient times, Egyptians, Babylonians and Chinese believed that life could arise by spontaneous generations from non-living things in addition to arising from parental organisms.
· The Belgian Plant Nutritionist Jean-Baptise Van Helmont (1577-1644 AD) even gave a recipe for the production of mice in 21 days from a dirty soaked shirt with a wheat barn, when kept in the dark.

3. Theory of biogenesis (Life from Pre-existing life)
· Life is originated not from inanimate substances but from their pre-existing forms, i.e., Omne vivum ex ovo (or vivo).
· It was developed by Francesco Redi, Italian biologist and physician, (1668AD) and followed by Italian investigator Abbe Lazzaro Spallanzani (1767AD) and French microbiologist Louis Pasteur (1867AD).
Redi's Experiment
· Francesco Redi, first of all, refuted the idea of spontaneous generation. He conducted experiments in three sets of jars containing meat. One set of jars was kept (left) open, the second one was covered with a fine net and the third one was with a piece of paper. He found little white worms and maggots only in the opened jar. In the other two sets of sealed jars, worms and larvae were developed outside the net and paper, but not inside the jar.
· He proved that maggots were not borne spontaneously but due to the contamination of meat by flies.
· He thus concluded that maggots arose only from pre-existing flies but not generated spontaneously from any other form of the material.

· Lazzaro Spallanzani experimentally proved that even primitive organisms can’t arise from non-living matter.
· He prepared flasks of meat broth (meat stock as a nutrient medium for bacteria) and boiled them for several hours. Some flasks were sealed and others were left open. Micro-organisms appeared in those opened flasks and sealed flasks remained sterile. He further concluded that air carried micro-organisms germinate when they got moisture and food. They have not formed abiogenetically.

· In Louis Pasteur’s experiment, he used a flask having a curved neck that would not allow the free entrance of dust particles and microorganisms into it. The flask contained water of brewer's yeast (greyish-yellowish fungus used as fermenting agent) with sugar, which was thoroughly boiled for several minutes. Then, the flask was allowed to cool. There was no growth of any organisms in the flask even after several days. After that, the curvature of the flask was broken making a large opening. After 24 hrs, Pasteur noted the growth of moulds (growth of minute fungi occurring in moist warm conditions) in the flask. From this experiment, it was concluded that the spores of the moulds found in the air easily entered the flask when its neck was open. So, the growth of moulds was possible in the liquid.

· Louis Pasteur disproved the spontaneous generation of bacteria from the decomposing broth.
· Pasteur was famous for the germ theory of diseases and immunology.
· The process of destroying all living organisms is called sterilization.
· The principle of sterilization is based on experiments carried out by Louis Pasteur.
· The theory of biogenesis is however not applicable to the origin of life because it did not explain the origin of life.

4. Cosmozoan theory or Theory of Panspermia
· Proposed by Ritcher (1865AD) and supported by Preyer (1880AD), Helmholtz (1884AD) and Arrhenius (1908AD).
· Life had come to the earth from some other planets or space in the form of resistant spores or cosmozoa of simple organisms in meteorites (pieces of rock falling from space on to earth).
· However, the possibility of some living beings coming from some other planet seems to be highly remote because interstellar space is full of 
(i) lethal radiations and 
(ii) high temperatures. 
This theory was discarded.

5. Theory of Eternity

· Also called steady-state theory
· Proposed by Preyer (1880AD)
· Different forms of living beings have always existed on the earth and shall continue to exist in the same form till eternity.
· This theory of eternity lacks scientific evidence and is not accepted.

6. Theory of Catastrophism
· Supported by Georges Cuvier (1769-1832AD) and Orbigney (1802-1837AD).
· According to this, catastrophic revolution (great destruction) occurs upon the earth from time to time which completely destroys all living beings.
· New organisms, then suddenly come from inorganic material.
· Each creation consists of life quite different from that of the previous one.

Origin of Universe and Earth

· The Universe originated 15-20 billion years ago through the thermonuclear explosion of cosmic materials (primaeval matter or Ylem) producing huge sounds called the Big Bang (Abbe Lemaitre, 1931AD).
· Due to the explosion (Big bang theory), cosmic materials broke up into innumerable pieces and expanded (believed to be expanded now).
· This was the beginning of a long cosmic evolution.
· Each piece formed a galaxy, which further broke up, expanded and formed many nebulae.
· Constellations are a group of stars.
· According to the Nebular hypothesis (Kent, 1755AD), each nebula which was large but cold clouds of dust and gases gave rise to one star and its planets.
· Nebular hypothesis was explained by Laplace (1796AD), and supported by Lemaitre (1931AD).
· One of the nebulae was the solar nebula which gave rise to the solar system some 4.6 billion years ago.
· Our solar system lies in the Milky Way (=Akash Ganga) galaxy. It is a spiral galaxy with numerous stars.
· Solar system consists of the Sun at the centre formed by the condensation of cosmic clouds/dust and planets, their satellites (moon), comets and asteroids at the periphery formed by swirling/spinning/rotation of the cosmic clouds/dust around the centre.
· The earth is one of the eight planets of the solar system revolving around the sun.
· It is 4.6 billion years old, 6.6x1021 tonnes in weight, approximately 12,800 kilometres in diameter and 40,000 kilometres in circumference at the equator.
· When formed 4.6 billion years ago, the earth was red-hot glowing mass (5000-60000C) of cosmic dust and gases with only one phase-gas comprising free atoms only.
· The first atmosphere of the earth was composed mostly of hydrogen which escaped into space because it was not held by gravity.

7. Biochemical evolution theory (Oparin and Haldane's Theory or Modern theory of the origin of life or Chemical theory or Naturalistic theory)
· Put forwarded by Russian Scientist Alexander Ivanovich Oparin (1894-1980AD) and an Englishman J.B.S. Haldane (1892-1994AD).
· It states that "life was originated spontaneously from some non-living inorganic compounds in the oceans of primitive earth about 3.7 billion years ago."
· Elements produced simple inorganic chemicals which, in turn, formed organic chemicals (e.g. Sugar, fatty acid, amino acid, pyrimidines, purines, nucleotides etc.). These, then, formed complex chemicals that formed Coacervates.
· Coacervates, nucleic acids and other chemicals, evolved into the primordial life.
· From primordial life, organisms were evolved.

· Oparin classified his theory into the following three steps.
A) Chemogeny (Formation of organic compounds from inorganic substances)

It is further sub-divided into the following five sub-headings.

i) Formation of Water, Ammonia, Methane and Cyanide
· The primitive atmosphere had the elements like carbon, hydrogen, nitrogen and oxygen. They were in a gaseous state due to very high temperatures. Due to a gradual decrease in temperature, they collided and combined to form molecules and compounds.
· Hydrogen atoms were most numerous and most reactive. Hydrogen combined with all available oxygen atoms and formed water.
· Free oxygen atoms were not available at that moment, so the primitive atmosphere was reducing.
· Hydrogen is also combined with nitrogen to form ammonia.
· Some hydrogen atoms combined with carbon to form methane.
· Carbon reacted with metallic atoms to form Carbides and Nitrogen also reacted with metallic atoms to form nitrides. 
· These molecules were considered as key molecules in the origin of life.
C + 2H2 → CH4 (Methane)
2H2 + O2 → 2H2O (Water)
N2 + 3H2 → 2NH3 (Ammonia)
2C + N2 + H2 → 2HCN (Hydrogen Cyanide)

ii) Formation of hydrocarbons
· When the temperature of the earth gradually cooled up to 100°C or even low, highly reactive free radicals like -CH and -CH2, condensed and formed varieties of saturated and unsaturated hydrocarbons.
CH + CH → C2H2 (Ethyne) [Unsaturated]
CH2 + CH2 → C2H4 (Ethene) [Unsaturated]
CH2 + CH2 → CH4 (Methane) + C [Saturated]

iii) Formation of Oxy and hydroxy derivatives of hydrocarbons

· These hydrocarbons reacted with steam and formed oxy and hydroxy derivatives of hydrocarbons (such as aldehydes and ketones).
C2H2 + H2O → CH3CHO

iv) Formation of carbohydrates, amino acids and fatty acids
· Due to condensation, polymerization, oxidation and reduction of the above hydrocarbons, complex molecules like simple sugar, amino acids and fatty acids were formed.
CH4 + H2O → Sugars; fatty acids
CH4 + H2O + NH3 → Amino acid - CO(NH2)2 
CH4 + HCN + H2O + NH3 → Nitrogen bases (purines, pyrimidines)

v) Formation of purines, pyrimidines and nucleotides Above hydrocarbons reacted with hot water, hydrocyanic acid (HCN), ammonia (NH3) and formed purines, pyrimidines and nucleotides.
· CH4 + HCN + H2O + NH3 → Nitrogen bases (purines, pyrimidines)
· Energy for the above reactions was available from direct UV rays of the sun, heat energy from volcanoes or high temperatures of the primitive earth, electric energy from lightning.
· Above reactions were presumed to be taken place in seawater, which had organic compounds.
· It was described as 'primordial soup' or 'hot dilute soup' or pre-biotic soup by Haldane (1920 AD); it was also referred to as ‘warm little pond’ by Darwin.

B) Biogeny (Formation of complex biomolecules)
· It can be described under the following sub-steps.
i) Formation of nucleic acids
· It is assumed that pentose sugar, phosphate and nitrogen bases combined to form nucleotides.
· Number of nucleotides combined to form DNA and RNA.
· The formation of nucleic acids (DNA and RNA) was a significant event as they were capable of self-duplication.
· They were considered as the first sign of origin of life.
· CH4 + HCN + H2O + NH3 → Nitrogen bases (purines, pyrimidines)
· Nitrogen bases + Pentose sugar + Phosphates → Nucleotides
· Nucleotides + Nucleotides → Nucleic acids (DNA and RNA)

ii) Formation of coacervates

· Nucleic acids and complex macromolecules of primordial soup are aggregated and bound by a water layer to form coacervates.
· Coacervates were the intermediate between molecules and organisms.

iii) Formation of primary organisms

· Coacervates absorbed organic substances from the ocean, grew in size, multiplied and formed anaerobic heterotrophs or first cells or protocells or protobiont.
· Protocells were similar to viruses.
· They gave rise to prokaryotic cells and eukaryotic cells.
Prokaryotic cells: Cells without definite nuclei. For e.g. Monera
Eukaryotic cells: Cells with definite nuclei. For e.g. Protista
· Monera gave rise to bacteria and cyanobacteria (blue-green algae).
· Protista gave rise to protozoa, metazoa and metaphyta.

· The chemical reactions resulting in the formation of carbohydrates, amino acids, fatty acids and other complex organic substances probably occurred in the sea which is described as hot dilute soup or primordial soup or pre-biotic soup.
· Protobionts- Amino acids, sugars, fatty acids and glycerol gave rise to polymers that may have assembled into spherical structures called protobionts.
· Protobionts made up of polypeptides- Microspheres (the term given by Sydney Fox, University of Miami, 1964AD)
· Protobionts made up of lipids- Liposomes
· Protobionts made up of polypeptides, nucleic acids and polysaccharides
· Coacervates (also called Pre-biotic structures by Oparin and created in the laboratory by Oparin and Fox).
· Eobiont (Pre-cell): A coacervate containing nucleoprotein, surrounded by several nutritive substances and covered by a surface membrane represent pre-cell or Eobiont or Protocell or First cell or Anaerobic chemoheterotroph.

C) Cognogeny (Modifications of life)
· Due to a shortage of food in seas, organisms had to change their feeding habit and became parasitic, saprophytic, chemo synthesizers, photosynthetic and so on.

Anaerobic, prokaryotic and chemoheterotrophic
Anaerobic, prokaryotic, chemoautotrophic (organisms using inorganic elements)
Anaerobic, prokaryotic and photoautotrophic (able to synthesize their food in sunlight)
Aerobic, prokaryotic and photoautotrophic
Aerobic, eukaryotic and photoautotrophic
Higher forms of metazoa and metaphyta

· Primitive earth had no bacteria and microbes to utilize macro-compounds as nutrients.
· Nowadays, no new life can originate as there are free Oxygen and microbes in the earth, therefore, macro-compounds can’t be accumulated.
· Free O2 present in earth oxidizes or destroys most of the intermediate products and no amino acids will be obtained in an oxidizing atmosphere, so new life can’t be originated today.

Miller and Urey's Experiment

· It is the experimental verification of · 
· Stanley Lloyd Miller, who was then a graduate student of Harold Clayton Urey at the University of Chicago in the U.S. and Harold C. Urey did a series of experiments and put Oparin and Haldane’s theory to test in 1953 AD.
· They tried to recreate the conditions that might have existed on earth in the laboratory.
· They set up the apparatus as given in the figure below.
· The apparatus was called ‘Spark discharge apparatus’.
· First of all, they evacuated the apparatus, made it sterile and then introduced a mixture of gases like methane (CH4), ammonia (NH3) and hydrogen (H2) into it (ratio 2:1:2).
· There was no free oxygen (reducing atmosphere).

The apparatus also contained
· Boiling water chamber to promote circulation and to provide necessary vapour for reaction (Oxygenation, To represent primitive ocean).
· Energy was supplied by the electric sparks from electrodes which was the stimulation of lightening.
· At one place a trap was provided to collect the products of the chemical reaction during the run.

· Conditions created were of gases, heat, rain, electric discharge like lightning as supposed to have existed on earth.
· The apparatus was made airtight and gases and water vapour circulated into it.
· The experiment was run continuously for a week.
· At the end, liquids in the trap were analyzed by paper chromatography.
· A total of 15 amino acids were isolated including glycine, alanine and aspartic acids (organic monomers).
· Urea, Hydrogen cyanide, Lactic acid and Acetic acids were also formed.
· Amino acids are the building blocks of proteins and proteins are the building blocks of living organisms.
· So, this experiment, therefore, carries a significant value in describing how the living organisms could have evolved out of the chemical compounds. (Temperature 800°C, simulation experiment, electric spark- 75,000 volt)
· The results of Miller’s experiment were discussed in the book “The Planets” written by Harold Urey.
· In another simulation experiment, Melvin-Calvin strongly irradiated CO2 and H2O in a Cyclotron and obtained formic, succinic and oxalic acids as end products.

Evolution + Evidence of Evolution

· Father/founder of the concept of evolution - Empedocles (493-435 BC)
· Father of modern applied ideas of evolution - Buffon (1707-1788 AD)
· Father of evolution/Term evolution was coined by Herbert Spencer (1820-1903 AD)
· Father of organic evolution- Charles Darwin (1809-1882 AD)
· Derived from 2 Latin words- (e- from, and volvere - to unroll)
· Charles Darwin in 1859 AD defined evolution as ‘Descent with modification', Evolution is a process by which related populations diverge from one another, giving rise to new species.
· Anthropoids gave rise to old world monkeys, apes and man. (Hominoid line- line remaining after the separation of old world monkeys).
· Changes in species over time/ Slow but continuous (Gradual) process/ branch of biology that deals with cumulative changes in the characteristic of organisms, over time in response to changes in an environment.
· History and development of race with variations
· Organic evolution is the process by which early forms of life, once originated, underwent gradual modification, with the changing environmental condition of the earth, to evolve into present-day diverse forms of life in millions of years.
· Three stages of evolution were given by Haeckel [BPKIHS 2002]. 

Evidence of Evolution

· Structure and origin– same, appearance and functioning- different [MOE 055, 062]

Examples of Homologous Organs
a) Structure and arrangement of bones of limbs of different vertebrates  

b) Basic plan of mouthparts of insects is the same but modified according to the mode of feeding. The mouthparts of cockroach, honey bee, mosquito and butterfly comprise labrum, a pair of mandibles and two pairs of maxillae but they perform different functions.
For example, Butterfly - siphoning, Housefly -sponging, Cockroach - biting and chewing, Honeybee - chewing and lapping, Mosquito - piercing and sucking.
c) Seven cervical vertebrae in mammals - All mammals have seven cervical vertebrae irrespective of their lengths of necks.
d) Thorns of Bougainvillea and tendrils of cucurbits (arise in auxiliary positions and are modified branches.)
e) Legs of different insects: Legs of insects are composed of five parts: coxa, trochanter, femur, tibia and tarsus. Except for tarsus, others are of a single segment.
Legs in mole cricket (forelegs), grasshopper (hindlegs), honey bee, mantids and water beetles are specialized for digging, jumping, collecting pollen, grasping prey and swimming respectively but in all these cases, the legs are formed of similar 5 podomeres.
f) Teeth of man
g) Penis and clitoris [BPKIHS 2002]
h) Testes and ovaries
i) Fin of fish and wing of bird [MOE 2003]
· Proves common ancestry- A group of quite similar organisms might have shared different habitats.
· Show adaptive radiation (Development of different functional structures from a common ancestral form). 
· The concept was given by H.F. Osborn in 1898.
· For example, modification in limbs of mammals from their common terrestrial and with the pentadactyl arrangement and divergent evolution. @ HOD= (Homologous- Origin same- Divergent evolution)

· Different structure and origin but same appearance and functioning

Examples of Analogous Organs
a) The wing of an insect or pterodactyl or bird or patagium of bat
· The wing of an insect is formed of a thin flap of chitin and stiffened by a series of 'veins'. It is operated by muscles attached to its base.
· In pterodactyl, the wing is an enormous fold of skin supported by an enormously enlarged fourth finger of the forelimb.
· In birds, the flight surface is formed by feathers attached to the bones of the forelimb.
· In bat, the wing is formed of a fold of integument (patagium), supported by the elongated and outspread phalanges of the last four digits (second, third, fourth and fifth digits.)
b) Eyes of Fish & Squids (Mollusca) - Function in the same way but their origin and structure are different.
c) Trachea of Insects / Vertebrates - [Used for respiratory purpose but the mode of development is different].
d) Stings of Honey bee / Scorpion - [Used for stinging but in the honey bee, the sting is modified ovipositor (the structure that helps in egg-laying) but in Scorpion, modified last abdominal segment]
e) Stem of Ruscus (modified into leaf-like) and leaf of any typical plant- both are photosynthetic regions.
f) Gill of Fish / Prawn (respiration)
g) Fins of Fish / Flippers of whales are analogous organs. Fins of fishes are not pentadactyl but flippers of whales are pentadactyl.
· Supports convergent evolution as a group of quite dissimilar organisms might have shared a common habitat, also called homoplastic organs.
· No evolutionary significance
· Sir Richard Owen formulated the concept of Homology and Analogy.
· Study of functional anatomy is called Tectology.


· Living animals with characters of two different groups of animals are called connecting links.
· Extinct animals with characters of two different groups of animals are called missing links.

Reptiles: Teeth, jaw, claw, tail, non-pneumatic bones Birds: beak, feathers, wings, 4 digits on each foot for perching, sternum with keel (distinct median ridge-like structure along the ventral part of avian sternum). Organism Archaeopteryx lithographica [KUMET 2000] [Aves]
Annelida: Worm-like body, non-chitinous cuticle, nephridia Arthropoda: Compound eyes, antennae, haemocoel, semi-jointed paired legs, trachea, and tubular heart with Ostia. Peripatus [MOE 2002] [Arthropoda]
Annelida: Gills, nephridia, trochophore like stage Mollusca: Shell, Mantle, Muscular foot. Neopilina [Mollusca]
Fish: Fin, scale, gill, lateral line system. Amphibia: Internal nares, lungs, 3 chambered heart Dipnoi [Lungfishes] (Proptopterus, Neoceratodus, Lepidosiren)
Non–chordates Chordates Balanoglossus [Chordata]
Cartilaginous fishes Bony fishes Chimaera (Rabbitfish)
Plant: Chloroplast, photoautotrophic nutrition Animal: Flagella, contractile vacuole, binary fission Euglena [Protozoa] [IOM 200]
Aquatic plants Land plants Fritschiella
Reptiles: Oviparous, variable body temperature (Poikilothermic), cloaca, some skeletal similarities Mammals: Hair, mammary gland, diaphragm Ornithorhynchus (Duck-billed platypus), Spiny anteater (Echidna, Lycaenops (Extinct reptile).
Living Non-Living Viruses
Fish Land vertebrates Coelocanthus
Ape Man Australopithecusrow12 col 3
Protozoa Porifera Proterospongia [Protozoa]
Amphibia Reptilia Seymoria [IOM 2007]

· Confirms the evolution of Arthropoda and Mollusca from annelids, amphibians from fishes and birds and mammals from reptiles.

Animals that underwent very little change during long geological periods.
· Peripatus, Limulus - (Arthropoda)
· Neopilina, Nautilus - (Mollusca )
· Lingula - (Branchiopoda, Crustacean)
· Latimeria - (Coelacanth fish)
· Sphenodon - (Reptilia)
· Didelphis - (Opossum- tree dwelling mammal)
· Lamprey – (Chordata- Cyclostomata)


· Rudimentary and functionless organs, organs of no use to the possessor.
· Weidershiem listed over 100 vestigial organs in man.

Examples of Vestigial organs in man are:
· Coccyx (Tail bone) [KUMET 2004]
· Wisdom (Third molar) teeth
· Nictitating membrane (Plica semi-lunaris or third eyelid)
· Body hair
· Ear pinna muscles or Auricular muscles [Indian Embassy 2002, 2006]
· Nipples in male
· Segmental muscles on the abdomen
· Vermiform appendix (Extension of caecum) [BPKIHS 2003; KUMET 2000]
· Melanocyte Stimulating Hormone
In other animals:
· Rudiments of pelvic girdles in Python
· Wings in flightless birds (Ostrich, Kiwi)
· Eyes of Proteus (Cave salamander )
· Reduced second and fourth metacarpals (splint bone in Horse )
· Pelvic girdle and Ear pinna of Whale
· Well developed vestigial organs in some animals and rudimentary vestigial organs found in other animals indicate their common ancestry.

· The reappearance of ancestral characters
· Confirms ancestral history
Examples of Atavism are:
· Long and dense hair in some men (Lions boy of Russia )
· Newly born baby with a small tail
· Multiple nipples
· Power of moving pinna in some person
· Cervical fistula in man

· In man, in the normal course, only one pharyngeal pouch perforates to form an opening from the pharynx to the exterior in the form of the external ear canal as Eustachian tube.
· But rarely, the neck may possess an Additional opening through which the throat or nasal cavity communicates with the exterior. This represents the opening of an Additional pouch to the exterior and is known as a cervical fistula.
· Homodont condition in many aquatic animals or Homodont dentition in piscivorous cetaceans

· Study of the development of an individual from fertilized egg to adult
· Embryos of different vertebrates.
· Development starts from a single cell and contains cleavage, morula, blastula and gastrula.
· Heart of vertebrates supports biogenetic law.
· Rule of embryonic development was given by Von Baer (1828AD).
· Biogenetic law/Recapitulation theory/Ontogeny recapitulates Phylogeny-Ernst Haeckel (1866 AD).
· Presence of gill slits (clefts) in vertebrate embryos - supports recapitulation.

· Study of the geographical distribution of animals and plants
· Alfred Russel Wallace divided the world into 6 major biogeographical regions called realms - Palaearctic, Nearctic, Ethiopian, Neotropical, Oriental, Australian.
· Palaearctic and oriental regions are separated by high mountain ranges.
· Galapagos Islands are called “a living laboratory of evolution”.
· Darwin studied twenty related varieties of the bird belonging to the family Geospizidae, differing in the shape and size of the beak. These birds are now called 'Darwin's finches.


· Study of fossils [MOE 2063; IOM 1998]
· Fossils is the remains of ancient organisms
· Fossils are found in sedimentary rock.
· Father of palaeontology- Leonardo da Vinci
· Founder of modern palaeontology- Georges Cuvier
· Age of rock is calculated on the basis of the amount of lead present.
· Written documents or Footprints of evolution.
· Geologists traced the evolutionary history of horses, camels, dogs, man and elephants with the help of the study of fossils.

Types of fossils: 
Unaltered, petrified, impressions, compressions, casts or moulds and amber.
i. Unaltered: Whole bodies, woolly mammoths were found buried in ice in Siberia.
ii. Petrified: Replacement of organic parts by minerals (Carbonates, Sulphates, Silicates, and Phosphates) is petrification, the most usual form of fossils- Bones, shells, teeth and trunk of trees.
iii. Impressions: Body parts of organisms when coming in contact with clay leave impressions on the soil. It later hardens to form rock. E.g. Feathers of Archaeopteryx.
iv. Compressions: Buried parts of organisms become flat due to overlying pressure. The outline is only left behind. Plant fossils.
v. Casts or moulds: Organism when gets submerged in water with lime, sediments surround the body in the form of the hard coat. They retain true copies of external morphology. E. g. Skeleton of Gastropods.
vi. Amber (Resin): Resinous secretion of certain coniferous trees.

Determination of Age of Fossil

· Age of fossil is determined either by radioactive carbon dating technique or by the amount of lead in the rock.
(a) Radioactive Carbon-dating Technique
· It is used to determine the age of recently found fossils. It is applicable to those specimens only which have carbon.
· Radioactive carbon has a half-life of 5568 years.
(b) The amount of lead in a Rock
· Uranium changes into the lead. The rate of this change is independent of the conditions under which it takes place.
· It has been estimated that one million grams of Uranium can produce 17,600 grams of Lead per year.
(c) Potassium-Argon method
· This method has recently been used to determine the age of hominid fossils in East Africa.
· The half-life of potassium40 is 1.3 * 10^9 years.

· History of evolution based on fossils.
· The prokaryotes were originated in Precambrian.
· Fishes originated in Ordovician, Amphibians- Devonian, Reptiles- carboniferous, dinosaurs- Triassic period.
· Mammals originated about 250 million years ago.

Animals Evolved or Originated Dominated or Age
Fishes Ordovician Devonian
Amphibians Devonian Carboniferous
Reptiles Carboniferous Jurassic or Mesozoic Era [IOM 2008]
Birds Jurassic Cenozoic Era
Mammals Triassic Cenozoic Era (Pliocene Epoch)
Dinosaurs Triassic (evolved), Jurassic (dominated), Cretaceous (Extinct) -
Archaeopteryx Jurassic Cretaceous
Invertebrates - Ordovician
Protista - Archaeozoic era

· Dinosaurs became extinct probably due to the direct hitting of a comet or a meteorite having rich amounts of Iridium.

Outline evolution of the horse
· The evolution of the modern horse proves the process of evolution by revealing that the earlier simpler forms have themselves changed into better-organized complex forms.
· Horse originated in the Eocene epoch in North America.
· First horse-like animal from which the modern horse (Equus) evolved was Hyracotherium (old name Eohippus).

Also, Read our other Notes Important for Entrance Exams:
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