1. Origin Of Life:

(i) Life is an inherent capacity that an organism possesses to maintain and reproduce itself.

(ii) The universe is a very vast and expanded region of space. It is possibly infinite in volume.

(iii) The galaxies are themselves very massive and contain many stars, planets and rocky bodies bound together with the gravitational forces and the clouds of gas and dust.

(iv) Origin of universe was the most important phenomenon in the origin of life. The Big Bang Theory (proposed by Georges Lemaître in $1931$ ) attempts to explain the origin of universe.

(v) This theory proposes that the universe is very old its origin took place almost $20$ billion ( $20 \times 10^{9}$ ) years ago with a single huge explosion (i.e., Big Bang).

(vi) In the solar system of Milky Way galaxy earth was supposed to have been formed about $4.5$ billion years back.

(vii) The gaseous envelope or atmosphere was not present on the early earth.

(viii) Due to volcanic eruptions, the molten mass was released which slowly covered the surface of earth. This also formed various gases released into the surroundings like methane, ammonia, carbon dioxide, water vapour etc.

(ix) The ultraviolet $(UV)$ radiations present in the sunlight acted upon water and broke up water into hydrogen and oxygen and lighter $h y d r o g e n$ escaped.

(x) Oxygen readily combined with other gases.

(xi) Therefore, free oxygen was not present on the primitive Earth.

(xii) Therefore, the early atmosphere was reducing unlike today’s oxidising atmosphere.

(xiii) The water vapour condensed to form water drops which fell as rain and slowly filled the depressions present on the surface of earth which is supposed to be the origin of large oceans seen today.

(xiv) But during all these changes, life appeared $500$ million years after the formation of earth or almost $4$ billion $(4 \times 10^{9})$ years back from now (as earth formed $4.5$ billion years ago).

2. Theories Of Evolution Of Life:

(i) Some scientists believe that the life came on the earth from other stars or planets in the form of spores or propagules.

(ii) The early Greek thinkers who said that the living organisms exist throughout the universe. This thinking was supported by Special Creation hypothesis, which believed God (or some supernatural power) created earth and life on earth.

(a) The Earth is merely 4000 years old and not billions of years.

(iii) The life was transferred from one planet to other in the form of some small units of life called spores or seeds or sperms. The transfer of spores was termed Panspermia.

(iv) The supporters of this theory stated that the life did not come from outer space. Rather there was a natural ‘spontaneous’ generation of the living organisms from non-living matter present on the earth. This is called Abiogenesis.

(v) However, this concept was experimentally disproved by many scientists, like Louis Pasteur.

(vi) Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life.

(vii) He showed that in pre-sterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from killed yeasts. This is called Biogenesis.

3. The Oparin-Haldane Chemogenic Hypothesis:

(i) Oparin-Haldane Chemical origin of life:

(ii) Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organism molecules (e.g. $RNA, protein, etc .$ ), and that formation of life was preceded by chemical evolution i.e., formation of diverse organic molecules from inorganic constituents.

(a) Oparin and Haldane proposed that the energy and stimulus were provided to these reactions by the conditions present on the early earth like

High temperature
Volcanic eruptions (storms)
Reducing atmosphere containing gases like methane, ammonia, etc.
Early atmosphere was reducing unlike present oxidising atmosphere because it had no free oxygen.

(b) $Stanley Miller and Harold Urey$ provided an experimental evidence of the chemical evolution in $1953$ in a laboratory set-up:

(iv) He sealed the gases $C H_{4}, H_{2}, N H_{3}$ and water vapour at $800 ° C$ in a closed flask and arranged of two electrodes in this flask.

(v) The electrodes created the electric discharge which provided the energy for the chemical reactions between these gases.

(vi) A condenser was attached to condense the gaseous compounds formed in the flask into the liquid form.

(a) After some time (days), he observed the formation of amino acids like glycine, alanine, and aspartic acid, in the flask from inorganic compounds.

(b) It is accepted on a large scale that complex organic molecules, i.e., $RNA$ , Protein, Polysaccharides, etc. were the first forms of life on the earth.

(vii) But they are the non-cellular forms of life because they were not the cells, rather the constituents of cells.

(viii) These giant molecules are supposed to be appeared approx. $3$ billion years back. They replicated and hence reproduced themselves perhaps and gave rise to the first cells.

(a) The first cells are supposed to be originated on earth about $2000$ million ( $2$ billion) years ago. They were essentially prokaryotes.

(b) All these life forms originated in water environment (oceans) and they were anaerobic chemoheterotroph.

(c) Hence, it is accepted by majority of the scientists that first Abiogenesis (origin of first form of life from non-living inorganic matter through evolutionary natural processes) and later Biogenesis.

4. Theories of Biological Evolution:

(i) Biological evolution is defined as any genetic change in a population that is inherited over several generations.

(ii) Evolution by natural selection, in a true sense would have started when cellular forms of life with difference in metabolic capability originated on earth

(iii) The essence of Darwinian Theory about evolution is natural selection

(a) The rate of appearance of new forms is linked to the life cycle or the life span

(b) For microbes, which show faster rate of division, this may happen in few days, and for multicellular animals or plants, millions of years.

(iv) Hence, there must be a genetic basis for getting selected and to evolve.

(v) Another way of saying the same thing is that some organisms are better adapted to survive in an otherwise hostile environment.

(vi) Adaptive ability is inherited.

(a) It has genetic basis.

(b) Fitness is the result of the ability to adapt and get selected by nature.

(vii) Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution

(viii) Branching descent explains the ‘pattern’ of evolution and natural selection explains the ‘mechanism’ of evolution.

(ix) With time, new life forms appear, and these new life forms arise as ‘branches’ from the previously existing life forms.

(x) Hence branching descent points towards the concept of common ancestry

(xi) The selection of ‘useful variations’ by nature is the main (but not exclusive) mechanism for evolution to occur

(xii) Thomas Malthus, an English naturalist, is widely known for his theories on populations and the increase or decrease in size of populations in response to various factors.

(a) One of the factors he studied was natural resources

(xiii) Every population has an inherent capacity to increase its number exponentially

(xiv) Natural resources like forests, water, air, food, etc. are limited in nature

(xv) The one who had ‘better’ adaptability survived and produced more progeny.

(xvi) A concept of ‘fitness’ and ‘natural selection’ was, thus, reflected in his theories

(xvii) Even before Darwin, Lamarck has proposed the theory of use and disuse.

Table showing summary of Lamarckism

	The ancestors of giraffe were bearing small neck and forelimbs and were like horses. These have internal vital force to increase their size and become relatively large in due course of time.
	Probably, due to some reasons, the surface vegetation was removed which lead to the stretching of neck to reach to the branches of trees. This stretching is induced by the scarcity of food in environment and need for the food. The changing environmental conditions always generate new needs. To fulfil new needs, an organism needs to make some changes in their structure.
	As the neck is comprehensively used to reach to the branches of trees, the elongation takes place. This is based on the proposition of use and disuse of organs the other organs of body say tail is not used so much hence, reduced or become unchanged. The continuous stretching of neck led to permanent elongation and character is acquired.
	The acquired character (i.e., long neck) is transmitted in next generation as the inheritance of acquired character is given by Lamarck. After several generations, the variations/modifications are accumulated to such an extent that they give rise to new species. This process of new species formation is called speciation.

(xviii) His theory was based on the hypothesis of

(a) Use and disuse of organs

(b) Inheritance of acquired characters

5. Darwinism:

(i) The main concept of Darwinian theory is natural selection.

(ii) He presented his theory after Lamarck’s theory. It is possible that the work of Thomas Malthus on ‘populations’ influenced Darwin

(iii) Thomas Malthus inspired Charles Darwin to frame his own theory of evolution based on the natural selection.

(iv) Darwin asserted that variations which are heritable, and which make resource utilisation better for few (adapted to habitat better) will enable only these to reproduce and leave more progeny.

(v) Darwin said that the ‘appearance’ of new life forms is due to accumulation of variations from one generation to another.

(a) He said that the appearance of new forms is linked to the life span of that organism.

(b) He said that every living organism, whether animal or plant has its own ‘characteristics’.

(vi) While moving from one place to another during his voyage, Darwin observed that even different looking and differently behaving organisms share some similarities among themselves

(vii) Darwin concluded that all the existing life forms share similarities to varying degrees and may share common ancestors.

(a) More are the similarities, more closely they are related and more closely they are related, more recently they shared common ancestors.

(viii) Nature poses the same challenges to all living organisms in the form of harsh climate, food scarcity, natural disasters like flood, droughts, etc.

(ix) The characteristics that enable some organisms to survive better than others in the same environment are said to be selected by nature. Some used the word ‘fitness’ for this capability to survive better.

(x) But Darwin only referred to the ‘reproductive fitness’ which means those organisms who are better fit in their environment produce more number of offspring’s than others, or, we can say their reproduction rate is higher than the others.

(xi) These, therefore, will survive more and hence are selected by nature. Darwin used the phrase ‘natural selection’ for this and said that it is the natural selection which is responsible for the evolution.

(xii) There was one more naturalist called Alfred Wallace, who worked in the Malay Archipelago.

(a) Like Darwin, he also talked about the fitness of organisms. He also came to the similar conclusions that those organisms which can adapt better in their environment are selected by the nature.

6. Evidences Of Evolution:

(i) Many important evidences are present in our nature which shows that evolution has indeed taken place on earth

(ii) Hence, fossils are the preserved remains of hard parts of the organisms (plants, animals etc.) like bones, teeth, shells, wood, etc. in the rocks

(iii) The earth’s crust shows rocks or sediments of different ages and it was interpreted that the organisms who died earlier, fossils are formed deeper layers and those who died later the fossils are formed upper layers.

(iv) Hence, new forms of life have arisen at different times in the history of earth. All this is called palaeontological evidence

(v) The age of fossils can be determined by following methods:

(a) Radioactive Carbon $(C^{14})$ Dating Method:

Discovered by WF Libby.
This isotope is only reliable for dating fossils less than $70000$ years.

(b) Radioactive Clock Method:

Discovered by Boltwood.
Based on the disintegrating property of radioactive elements.

The transformation of potassium into argon; rubidium into strontium has been used for dating fossils bearing rocks of any age and any type.

(d) Electron Spin Resonance $(ESR)$ Method:

Most reliable and accurate method.
It is because the background radiation causes electron to dislodge from their normal positions in atoms and trapped in crystalline lattice of material, it is mostly used to date $C a C O_{3}$ and limestone.

7. Comparative Morphological and Anatomical evidences:

(i) Morphology refers to the external structure of an organism and anatomy refers to the internal structure and functional organisation

(ii) By comparing the morphology and anatomy, we can find the similarities as well as differences between the present living and remote extinct organisms

(iii) The structures in different organisms which have similarity in their anatomy or basic plan but serve different functions are known as homologous structures

Table: Homologous and analogous organs:

Homologous organs	Analogous organs
They are structurally same	They are structurally different
They are functionally different	They are functionally same
They show divergent evolution	They show convergent evolution
Forelimbs of bat, whale, horse, man. Bulb of onion and phylloclade of cactus. Thorn of Bougainvillea and tendril of Cucurbita.	Wings of bird and wings of insects. Sweet potato and potato Eye of the octopus and of mammals Flippers of Penguins and Dolphins.

8. Embryological evidences:

(i) Embryological support for evolution was also proposed by Ernst Haeckel based upon the observation of certain features during embryonic stage common to all vertebrates that are absent in adult.

(ii) According to Ernst Haeckel, ontogeny (development of embryo) is recapitulation of phylogeny (the ancestral sequence). This view is summarised by his Biogenetic Law: Ontogeny recapitulates phylogeny.

(a) Von Baer disapproved this theory.

9. Natural and Artificial Selection:

(vi) Artificial selection, as the name depicts, is the selective breeding of plants or animals for desired traits.

(vii) It is done artificially by employing various breeding methods and that is why it is called artificial selection.

(viii) Following are the examples of artificial selection.

(a) Generation of different breeds of dogs, cows, sheep.

(b) Generation of different vegetables like Broccoli, Kale, Cauliflower, etc. from wild cabbage.

(ix) Natural selection as an evidence of evolution can be demonstrated:

(a) Industrial melanism, which supports the appearance of the darker coloured moths on the industrialised areas after the industrialisation in England, and relative few numbers of white moths in the same area.

(b) This phenomenon depicted the camouflage ability of the moths which got naturally selected.

(c) This is also supported by the observation of more abundance of white moths in the rural areas as compared to dark-coloured ones.

(x) We continuously use drugs and antibiotics against microbes.

(a) With course of time, some microbes developed ‘resistance’ against these drugs by brining changes or modifications in their structures.

(b) Those which became resistant, survived, and hence selected by the nature.

(xi) Hence, developing ‘drug resistance’ by microbes is also an example of natural selection.

(xii) Moreover, this kind of natural selection took place in a small period, i.e., months or years and not centuries.

(a) Similarly, herbicide and pesticide resistance developed in the weeds and pests respectively after prolonged use of herbicides and pesticides.

(xiii) This is also an example of natural selection which supports the process of evolution.

(xiv) All these evidences suggest that evolution is a stochastic process which is based on many probabilities.

(xv) It is based on chance events in the nature and chance mutations in the organisms

(xvi) Hence, many probabilities are there for every phenomenon occurring in the nature and evolution cannot be seen as a directed process in the light of determinism.

10. Connecting links:

(i) These are extant organisms showing characters of two different phyla, group of organisms.

(ii) Missing links are extinct organisms showing characters of two different phyla, group of organisms.

Link	Between the Groups
Virus	Living and non-living
Peripatus (walking worm)	Annelida and Arthropoda
Balanoglossus	Chordates and Non-chordates (connecting link)
Archaeopteryx	Reptiles and Birds (missing link)
Cycas	Pteridophytes and Gymnosperms (connecting link)
Echidna (spiny anteater)	Reptiles and Mammals (connecting link)
Euglena	Animals and Plants (connecting link)
Gnetum	Gymnosperms and Angiosperms (connecting link)
Neopilina	Annelida and Mollusca (connecting link)
Ornithorhynchus (duck-billed platypus)	Reptiles and Mammals (connecting link)
Proterospongia	Annelida and Arthropoda (connecting link)
Protopterus (lung fishes)	Bony fishes and Amphibia (connecting link)
Xenoturbella	Protozoa and Metazoa (connecting link)
Sphenodon (living fossil lizard)	Amphibia and Reptilia (connecting link)
Seymouria	Amphibia and Reptiles (missing link)
Latimeria	Pisces and Amphibia (connecting link)
Myxomycetes	Protista and Fungi (connecting link)
Actinomyces rickettsia	Bacteria and Fungi (connecting link)
Chimaera (rabbit fish/rat fish)	Cartilaginous and Bony fishes (connecting link)

11. Adaptive Radiation:

(i) Darwin observed tremendous amount of diversity in organisms in The Galápagos Islands.

(ii) These are considered as Darwin’s finches.

(iii) There ware very high numbers of variations in the beak structure of the birds

(iv) All these varieties might have evolved in the Island itself

(v) It must have arisen from a basic seed-eating habit.

(vi) Evolution might have allowed insectivorous and vegetarian food habit.

(vii) This process of evolution of different species in each geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation.

(viii) He conjectured that these varieties evolved from the original seed-eating ancestor bird which was present in the South America.

(ix) Some of them flew to these islands and according to the needs of different environments, they developed different shapes of beaks and feeding habits. Some became insect eating, some fruit eating, some cactus eating.

(x) Another example is Australian marsupials, that show adaptive radiation.

(xi) Number of marsupials, each different from the other, like Koala, Kangaroo, Wombat, etc. originated from an ancestral marsupial, but all within the Australia

(xii) The placental mammals also underwent the adaptive radiation and developed into different varieties

(xiii) It was seen that many placental mammals resembled the marsupial mammals not only in structure but also in leading the similar ways of life.

(xiv) These similarities in these two different types of mammals (marsupials and placentals) are due to living in the similar ecological niches

(xv) The convergent evolution resulted in the origin of similar looking members in both the groups, e.g., Placental wolf and Tasmanian wolf -marsupial.

12. Hardy Weinberg's Principle:

(i) This principle states that a population is said to be in genetic equilibrium if it is not undergoing any kind of evolutionary change.

(ii) Genetic equilibrium means that the frequency of occurrence of alleles of a gene is supposed to remain fixed and even remain the same through generations.

(iii) Hardy-Weinberg principle stated it using algebraic equations. Main concepts of this principle are:

(a) This principle says that allele frequencies in a population are stable and is constant from generation to generation.

(b) The gene pool (total genes and their alleles in a population) remains a constant. This is called as genetic equilibrium.

(iv) Hardy-Weinberg principle says that the sum total of all the allelic frequencies of a gene is $1$ and the possible frequencies of above-mentioned genotypes, i.e., $A A$ , $a a$ and $A a$ are $p^{2}$ , $q^{2}$ and $2 p q$ , respectively. So mathematically this statement can be written as

(a) $p^{2} + 2 p q + q^{2} = 1$

(v) Therefore, if any of the following phenomena occurs, change in frequency of alleles takes place that may result in the evolution:

(a) Gene migration or gene flow is the phenomenon of movement of alleles from one population to another is called gene migration, it can either occur by

Migration of a section of population from one area to another
Interbreeding between members of two populations resulting in interchange of alleles

(b) Genetic drift is said to operate in small populations. If the addition and deletion of genes occur by chance, it is called genetic drift.

It may be because of any of the reasons like
Failure of a particular section of population to reproduce.
Death of individuals
Immigration or emigration

(vi) Genetic drift may result in the Founder effect.

(a) Sometimes some individuals move or drift far away from one population to another population in such a way that they become founders of a new isolated species.

(b) This is because these so called ‘founders’ carry certain rare genes which form new combinations of alleles in the new population. Hence, the change in allele frequency is so different in the new sample of population that they become a different species.

(vii) Hugo de Vries talked about mutations.

(a) The sudden appearance of variation is called mutation.

(b) Mutations are random or indiscriminate towards any particular change.

(c) nd when these mutations are selected by nature, then this will result in the appearance of new morphological or behavioural traits, i.e., new phenotypes, in that population.

(d) If this occurs for long time over few generations, then this would result in the formation of new species or Speciation

(viii) During gamete (sperm or ovum) formation, the alleles present on the parental chromosomes separate and form new combinations.

(a) This results in the genetic recombination.

(b) The crossing over during meiosis is a major source of variations in a population. The offspring produced from these gametes show ‘new’ combination of characters and are called recombinants

(ix) Nature selects those variations which are heritable (i.e., able to be inherited) and which make the survival better so that the individuals bearing these useful variations are enabled to reproduce and thence produce a greater number of progeny.

(x) Hence, natural selection also leads to change in allelic frequencies. However, the effects of natural selection on different traits can be

(a) Stabilising

(b) Directional or

13. Mechanism Of Evolution:

(i) Speciation is an evolutionary process by which new species arise.

(ii) According to Darwin, inheritable variations are the cause as they keep on accumulating from one generation to other and, ultimately, give rise to new species.

(iii) According to Hugo de Vries, who conducted experiments on evening primrose, the variations are brought about by mutations.

(iv) According to him, ‘mutations’ were the cause of evolution and not the minor variations that Darwin talked about.

(v) Mutations are the large changes arising suddenly in the genomic sequence (the $DNA / RNA$ sequence) of an organism. These mutations arise suddenly in a population and those mutations which arise in the germ cells of an organism pass on to the next generation.

(vi) There are some basic differences in Darwin’s understanding and Vries theory:

Darwin view on evolution	De Vries view on evolution
Mutations are small, cannot bring the sudden changes	Mutations are large, can bring sudden changes
Changes occur only when mutations accumulate	No need of accumulation
Evolution is slow and gradual	Evolution is sudden and faster

14. Modern Synthetic Theory Of Evolution:

(i) This mainly talks about the various modes in which evolution takes place

(ii) The raw materials for modern synthetic theory included:

(iii) Genetic variation

(iv) Natural selection

(v) Reproductive isolation

15. Geological Time Scale:

(i) The eras Palaeozoic, Mesozoic and Cenozoic are shown along with their periods like Silurian, Jurassic, Quaternary, etc., in the order of their occurrence from below upwards

(ii) Chlorophyte ancestors are the aquatic green algae which are supposed to give rise to all the green land plants (i.e., Bryophytes and Tracheophytes).

(iii) The first cell appeared about $2000$ million years ago (mya) on earth.

(iv) Some of these cells had the ability to release oxygen.

(v) The reaction could have been like the light reaction in photosynthesis where water is split with the help of solar energy captured and channelised by appropriate light harvesting complexes.

(vi) These cellular forms which evolved $O_{2}$ on early earth, in a way, performed light reaction of photosynthesis

(vii) Slowly these single-celled organisms became multicellular life forms and gradually evolved from less developed to more developed organisms.

(viii) Life began in water and slowly life forms invaded the earth but the first organisms that invaded earth were plants

(ix) Invertebrates (lower animals) evolved around $500 mya$ and became active during that period. They are still existing on earth but some forms have become extinct

(x) The jawless fishes (Agnatha) probably evolved around $350 mya$ .

(xi) There were some jaw-bearing fishes which had strong and stout fins with the help of which they could move on land and go back to water.

(xii) These were a type of bony fishes and they also evolved around $350 mya$ .

(xiii) These were called lobe-fins and were thought to be extinct but in $1938$ in South Africa, a fish was caught which was found to be a lobe-fin (Coelacanth).

(xiv) These lobe-fins are thought to be evolved into the first amphibians. The amphibians are the organisms that can live on both land and water.

(xv) First amphibians have now become extinct and there are no specimens of these left with us.

(xvi) Reptiles lay thick shelled eggs which do not dry up in sun unlike of amphibians.

(xvii) The amphibians evolved into the reptiles, many of which have become extinct from the earth, e.g., dinosaurs.

(xviii) Modern day descendants of reptiles are turtles, tortoises and crocodiles which are living.

(xix) As we know that, reptiles were the first true land inhabiting animals but probably $200 mya$ , some of the land reptiles went back into the water and evolved into fish-like reptiles

(xx) About $65 mya$ , dinosaurs suddenly disappeared from earth and various reasons were given for their extinction. The exact reason(s) is/are not known

(xxi) The mammals evolved from reptiles and first mammals were small-sized, like shrews

(xxii) As Australia got separated from the other continents, its pouched mammals (marsupials) prevented from facing any threat or competition from the mammals of other continents and hence, they survived and diversified on the Australian land better.

Era	Period	Epoch	Geological and Climatic Conditions	Flora (Plant Life)	Fauna (Animal Life)
Cenozoic (Age of Mammals)	Quaternary	Recent (Holocene)	End of last ice age; climate warmer; climatic zones distinct.	Dominance of herbs.	Age of man; development of human cultures.
		Pleistocene	Periodic continental glaciers in North.	Increase of herbs, spread of herbs and grassland.	Age of man, extinction of many large mammals.
		Pliocene	Cool and temperate climate away from the equator, continuous rise of mountains of Western-North America.	Decline of forests, great decrease of woody plants.	Abundance of mammals like elephant, horses and camels, humans evolving.
	Tertiary	Miocene	Cooling of climate.	Development of grasses, reduction of forests.	Mammals at height of evolution, first man-like apes.
		Oligocene	Lands lower, climate warmer.	Worldwide tropical forests, rise of monocots and flowering plants.	Archaic mammals extinct, appearance of modem mammals.
		Eocene	Zoned climatic belts well established.	Extension of angiosperms.	Placental mammals, diversified and special bed; hooted mammals and carnivores established.
		Palaeocene	Development of climatic belts.	Modernisation of angiosperms.	Evolutionary explosion of mammals.
Rocky Mountain Revolution (Little Destruction of Fossils)
Mesozoic (Age of Reptiles)	Cretaceous	-	Birth of modem reptiles, development of climatic diversity.	Rise of flowering plants especially monocotyledons, decrease of gymnosperms.	Dinosaurs become extinct, toothed birds became extinct; beginning of teleost fishes and modern birds; archaic mammals common.
	Jurassic	-	Culmination of worldwide warm climates.	Cycads and conifers common; appearance of first known flowering plants.	Dominance of dinosaurs, appearance of first toothed birds: rise of insectivorous marsupials.
	Triassic	-	Continents exposed, world subtropical climates.	Gymnosperms dominant, declining towards the end extinction of seed fem.	Transaction of reptiles to mammals, rise of progressive reptiles and egg laying mammals, extinction of primitive amphibians.
Palaeozoic	Permian	-	Rise of continents; climate became arid and varied, glaciation in Southern Hemisphere.	Dwindling of ancient plants, decline of lycopods and horse tails.	Extinction of ammonites and trilobites, abundance of primitives reptiles; appearance of mammals-like reptiles, decline of amphibians.
	Carboniferous	-	Climate uniform, humid at first cooler later as land rose; spread of tropical seas.	Mosses and seed ferns dominant, gymnosperms increasingly widespread (early coal forest).	Rise of insects, sea lilies at peak, spread of ancient sharks.
	Devonian	-	Broad distribution of uniform climates; increased temperature.	First forests, first gymnosperms and first known liverworts, horsetails and ferns.	Diversification in fishes; sharks and lung fishes abundant, evolution of amphibians.
	Silurian	-	Slight climate cooling extensive continental seas.	First known land plants club mosses, algae dominant.	Wide expansion of invertebrates, fist insects, rise of fishes.
	Cambrian	-	Warm climate, great submergence of land.	Land plants probably first appeared; marine algae abundant.	First indication of fishes, corals and trilobites abundant, diversified molluscs.
	Ordovician		Climate became progressively warmer.	Algae, fungi and bacteria; first fossils of plant life.	Invertebrates numerous and varied, most modem phyla established.
Proterozoic		-	Cool climate, volcanic eruptions, repeated glaciating.	Primitive aquatic plants algae, fungi, and bacteria.	Shelled protozoans, coelenterates, flatworms, primitive annelids.
Archaeozoic		-	Great volcanic activities, no recognisable fossils, indirect evidence of living things from some sedimentary deposits of organic material in rocks, e.g., Eubacterium isolatum, Archaeospheroides banbertonis.

16. Human Evolution:

(i) Human (class Mammalia) evolution is generally studied with the evolution of apes as they are closely related to man than any other animal. In human evolution, we specially study

(ii) The evolutionary history of genus Homo

(iii) There were some primates like Dryopithecus and Ramapithecus, etc. which evolved before man.

(iv) Human evolution is studied under three major stages:

(a) Ape stage including Dryopithecus, Ramapithecus, Shivapithecus, etc.

(b) Ape-man stage represented by Australopithecus.

Table: Human evolution:

Human ancestor	Common name	Cranial capacity	Origin	Characteristics
Dryopithecus	…	Like apes	Africa, 14-15 mya	Ape-stage of human evolution
Ramapithecus	…		Edward Lewis, Shivalik hills of India	Ape-like man. This organism was evolved from Dryopithecus and appeared some 14-15 million years ago. Strikingly, its molar and other dental structures were like human.
Australopithecus	Taung baby	450 to 500 cc	Africa, Pleistocene period, 4-5 mya	Discovered by Raymond Dart in 1924. They essentially ate fruits, but evidence shows that they hunted with stone weapons. They showed a bipedal movement and a semi-erect posture.
Homo habilis	Handy man, Tool-maker man	650 to 800 cc	East Africa, Pleistocene period, 2 mya	L. S. B. Leakey in 1960 discovered.
Homo erectus erectus	Java man	800 to 1000 cc	Central Java, Late Pleistocene, 1.7 mya	They had protruding jaws, small canines, projecting brow ridges, and large molar teeth.
Homo erectus pekinensis	Peking man	850 to 1200 cc	China, Late Pleistocene, 1.5 mya	They show similarities with Java man.
Homo erectus heidelbergensis	Heidelberg man	1300 cc	Germany, Late Pleistocene, 1.5 mya	Germany in 1907 by Daniel Hartmann. Carnivorous, used stone tools.
Homo sapiens neanderthalensis	Neanderthal man	1400 cc	Germany, Late Pleistocene, 0.1 mya	They were having heavy brow ridge and humped back, Neanderthal man was a legendary cave dweller. They were skilled hunters and true predators.
Homo sapiens fossilis	Cro-Magnon man	1600 cc	France, Holocene, 35000 years ago	Discovered in 1868 from Cro-Magnon rocks of France by MacGregor. They evolved from 35000 years to 20000 years ago.
Homo sapiens sapiens	Modern man	1450 cc	Africa, recent	Man with all modern features.

(v) When skull of adult modern human being is compared with skull of baby chimpanzee, it is found that more similarities exist in the jaw structure and facial bones arrangement, as compared, to the skull of adult chimpanzee.

(vi) For an example, the jaw of adult human skull resembles more with jaw of baby chimpanzee as adult chimpanzees have protruding jaws (projecting outwards). This shows that the apes and modern man shared common ancestors.

(a) The Homo sapiens sapiens arose in Africa and moved across continents and developed into distinct races.

(b) Modern Homo sapiens or today’s man evolved around $75,000 - 10,000$ years ago.

(c) This age period was called ice age (the geological period of long – term reduction in temperature of Earth’s surface and atmosphere) as during this age, the earth’s temperature was low consistently.

For an example, the jaw of adult human skull resembles more with jaw of baby chimpanzee as adult chimpanzees have protruding jaws (projecting outwards). This shows that the apes and modern man shared common ancestors.

11.

Important Questions on Organic Evolution

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