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Big-Bang Theory : 

Proposed by Abbe Lemaitre.

According to it, the universe originated about 20 billion years ago due to a thermonuclear explosion.

This thermonuclear explosion is called Big-bang.

Flat-disc like structure is called SOLAR-NEBULA formed.

About 4.5 billion years ago, the origin of our solar system took.

The very hot central part of this solar Nebula became still hotter & converted into the sun. Now, due to condensation of atoms & dust particles moving around the sun, formation of the other planets took place [Mercury, venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune].

The solid part of our planet earth was called Lithosphere & the gaseous part was known as atmosphere.

When the earth's surface cooled down and its temperature decreased to 100°C, water formed on it.    

 

Ancient Theories for origin of life :       

1.   Theory of special creation  –

The greatest supporter of this theory was father Suarez According to Bible life and everything was created by god in 6 days.  

on first day     : Earth and heaven

on second day : Sky and water    

on third day    : Land and plants 

on forth day    : Sun, moon and stars        

on fifth day     : Fishes and birds 

on sixth day    : Land animals and first man Adam and from his 12th Rib first woman Eve.

According to hindu mythology the world was created by God Brahma. (The first man was Manu and the first woman was Shraddha)

According to it life has not changed ever since its origin.

Special creation theory lacks scientific evidences so is not accepted.

 

2.  Theory of Spontaneous Generation (Abiogenesis or Autogenesis) – 

This hypothesis was supported by ancient Greek philosophers like Thales, Anaximander, Xenophanes, Plato. Empedocles, Aristotle.

According to this theory life was originated from nonliving things spontaneously.

They believed that the mud of the Nile river could give rise to frogs, snakes, crocodiles.

Abiogenesis was strongly supported by Von Helmont. He claimed formation of mice in 21 days. If a sweat soaked dirty shirt is kept in wheat barn.

 

3.   Cosmozoic Theory – 

Proposed by Richter.

Protoplasm reached on earth in the form of spores or other simple particles from some unknown part of the universe with cosmic dust and they gave rise to various forms of life. 

 

4.   Cosmic panspermia theory – 

Proposed by Arrhenius.

According to this theory organisms existed throughout the universe and their spores could freely travel through space from one star to the other.

 

5.   Theory of Eternity of Life – 

Helmholz believed that life is immortal.

 

Question for Evolution - Class 12, Biology
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According to the Theory of Special Creation, how was life created on Earth?
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6.  Theory of Biogenesis – 

Harvey (1651) and 

Huxley (1870)

{Omnis vivum ex ovo or vivo.}

New organisms can be originated on earth only by pre-existing life.

This theory rejected the theory of Spontaneous generation but cannot explain origin of life.

To prove Biogenesis and to disprove abiogenesis experiments were performed by  –

Francesco Redi (Italian 1668) – 

He took cooked meat in three jars, one was uncovered, the second was covered with parchment and the third was air tight.

He observed that maggots developed only in the uncovered jar while maggots could not develop in the meat in closed jars.

This proved that larvae were formed from eggs laid by the flies in open jars. Since the meat in closed jars could not be visited by flies so no larvae could develop. Therefore life originated from pre existing life.

 

Lazzaro Spallanzani (Italian 1767)  –

He boiled vegetables and meat to prepare a sterlized nutritive soup and he kept some of it in air sealed flasks and some in loosely corked flasks.

He observed that the soup in sealed flask remained sterile while micro organisms appeared in the soup in loosely corked flasks.

Thus even micro organisms were formed from pre existing ones in the air rather then spontaneously.

Evolution - Class 12, Biology

Louis Pasteur (French 1862) – 

Pasteur is popular for Germ Theory of Diseases or Germ theory and he disproved abiogenesis.

He prepared sterlized syrup of sugar and yeast by boiling them in flasks.

He took two flasks one of broken neck and another of curved neck (swan neck flask). No life appeared in swan neck flask because germ laden dust particles in the air were trapped by the curved neck which serves as filter while in broken neck flask colonies of microorganism were developed.

Modern theory of origin of life :

(Oparin-Haldane theory of origin of life)

Naturalistic theory Or Theory of Chemical Evolution –

This theory was proposed by Russian Scientist A.I. Oparin and J.B.S Haldane (England born Indian scientist)

Oparin's theory was published in his book 'ORIGIN OF LIFE'.                

 

Important Points

–  According to this theory life originated by the composition of chemicals. (Chemical evolution).

–  Oparin's theory is based on Artificial Synthesis. So also called as artificial synthetic theory.

–  Ist life originated in the water of oceans. So water is essential for origin of life.

     There is no life on moon due to absence of water. 

–   At the time of origin of life free Owas absent, so first life was anaerobic.

–   In the primitive atmosphere free oxygen was present but complete oxygen consumed in composition so
primitive atmosphere of earth was reducing.

–   Oxygen was reproduced by photosynthesis and atmosphere converted in oxydising.         

 

Chemical Evolution :

1.   The atomic stage – 

The earth was originated about 4.5 billion years ago. Early earth had free atoms of all elements which are essential for the formation of protoplasm.

The lightest atoms like carbon, hydrogen, nitrogen and oxygen formed the primitive atmosphere.

  Evolution - Class 12, Biology

2.   Molecular stage (Origin of molecules and simple Inorganic compounds) – 

Free atoms combined to form molecules and simple inorganic compounds.

Due to presence of high temperature, active hydrogen atoms combined with all oxygen atoms to form water and leaving no free oxygen.        

Thus the primitive atmosphere was reducing (without free oxygen) unlike present oxidising atmosphere (with free oxygen).

Hydrogen atoms also combined with nitrogen to from NH3.

(The first molecular compounds formed were probably water and Ammonia).

These Lighter elements also formed CO2 ,  CO, N2 , H2 etc.

 

3.   Origin of early organic compounds –  

The nitrogen and carbon of the atmosphere combined with metallic atoms forming nitrides and carbides.
Water  vapour and metallic carbides reacted to form to first organic compound Methane (CH4). Later on
hydrogen cyanide (HCN) was formed .

Water which formed on earth due to high temperature evaporated so clouds were formed.

Water vapour changed into rain drops and by the collection of water on earth primitive oceans were formed.

 

4.   Origin of simple organic compounds – 

Water of primitive oceans contained large amount methane, ammonia, hydrogen, cyanides, carbides, nitrides.

These early compounds interacted and formed simple organic compounds like, aldehyde, Ketones. Alcohols
Pentose and hexose sugar, Amino Acids, Glycerol, Fatty Acids, Purines, Pyrimidines etc.   

Energy was obtained from  U.V. Rays of sunlight, cosmic rays and heat of volcanic eruptions.

 

5.   Origin of complex organic compounds – 

The small simple organic molecules combined to form large complex organic molecules, e.g –

–    Amino acids Joined to form polypeptides and proteins, which were non-enzymatic.

–    Simple sugar units combined to form polysaccharides.

–    Fatty acids and glycerols united to form fats and lipids.

–    Sugar, nitrogenous bases, phosphates combined into nucleotides which polymerized into nucleic acid,

       which unable to replicate.     

                 

These macromolecules forms main component of protoplasm hence the possibility of origin of life in primitive oceans could be established.

After long time the water of primitive oceans became rich mixture of organic compounds as a result of

chemical evolution.

Question for Evolution - Class 12, Biology
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During the atomic stage of chemical evolution, which elements formed the primitive atmosphere on early Earth?
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Haldane called this saturated water of oceans as prebiotic soup or hot dilute soup.

The major requirement for promoting polymerization is the availability of continuous source of energy and removal of water from the surface of reactants so that they can concentrate and prevent depolymerisation.

======================================================================== 

Miller Urey, Louis Pasteur Experiment and Biological Evolution : Darwanian Theory, natural Selection - Evolution, Biology, Class 12

Experimental evidence for formation of simple organic compounds – 

By Stanley Miller who was a student of Harold Urey.  

In this experiment Miller took the mixture of methane, ammonia and hydrogen (ratio 2 : 1 : 2) in a large flask and passed steam over it by boiling  water and connecting it with a glass tube.

Electric spark discharged in the mixture by using two tungsten electrodes as source of energy. 

After 18 days this fluid was collected and analysed. This dark red fluid was found to contain.

–    Simple amino acids – glycine, alanine, aspartic acid.

–    Simple organic acids – formic, acetic, oxalic, lactic, succinic acids.

–    Pentose, hexose, aldehyde, ketone etc. 

Evolution - Class 12, Biology
Evolution - Class 12, Biology

 

BIOLOGICAL EVOLUTION : 

(i) Origin of  Protobionts and Nucleoprotein (Coacervates) 

Macromolecules which were synthesized abiotically in primitive ocean later came together and formed large colloidal drop like structures named as Protobionts (Later called coacervates by oparin, Fox and called them Microsphere and Deamer called them vesicles).

Evolution - Class 12, Biology

Each protobiont was cluster of macromolecule.

They contain proteins, nucleic acids, lipids, polysaccharides etc.

They grew by absorbing molecules from their environment.

They could divide by budding like bacteria, many chemical reactions including the decomposition of glucose took place inside the protobionts.

The sun provide energy for chemical reaction.

According to oparin coacervates were the first sole living molecules which gave rise to cell. 

Evolution - Class 12, Biology

 

(ii) Origin of protocells [Eobiont : 

The first living form named protocell originated in the primitive oceans.

The protocell were clusters of nucleo-proteins which formed by composition of nucleic acids and

enzymetic proteins.

Nucleoproteins had the property of self duplication.

Nucleoproteins were first sign of life. 

The protocell represented the beginning of life.

From protocells or eobionts few core of nucleoproteins gets separated free in oceans and became inactive but when they enter in another eobionts they became active so virus like structures were formed.

Origin of virus like structure is an example retrogressive evolution (complex to simple).

 

Important

1. Khorana (1970)artificially synthesized 77 nucleotide RNA molecule out side a living cell which suggests that probably RNA was the primordial genetic material rather than DNA. 

Zaug, Thomas cech and Altman described that some RNA molecules have enzymatic activity hence probably the RNA enzymes called ribozymes were able to replicate the primordial RNA. 

The discovery of RNA molecule working as enzyme has also changed our thinking about origin  of  life. 

It is now believed that about 4 billion years ago earth was an 'RNA world' in which RNA molecule carried out all the process of life without the help of either protein or DNA, 

By this discovery evolution is named as RNA world.

 

2. It is estimated that life originated about 3.0 billion years ago as protocell (eobionts) in precrambian era which was anaerobic heterotrophic. 

(iii) Origin of Prokaryotes – 

As a result of mutation the protocells became more complex and efficient and used the materials available in the surrounding medium and condensed themselves into prokaryotic cells.

Thus the first living being were prokaryotic, like bacteria they were single celled and consisted of naked DNA. Nutritionally they were chemoheterotrophs (saprotrophs), respiration was anaerobic.

(iv) Origin of Autotrophism – 

It includes the origin of chemosynthesis and photosynthesis.

(a) Origin of chemosynthesis : 

Due to continue withdrawal of organic molecules by chemoheterotrophs organic material decreased in oceans.

Before the organic material disappeared in sea, new modes of Nutrition developed, one of them was

chemosynthesis.

The organism which perform chemosynthesis are called as chemoautotrophs. They were anaerobic and synthesise organic molecules from inorganic material. The energy was obtained by oxidizing inorganic materials present in the sea.

Such mode of nutrition is found in Bacteria e.g. sulphur bacteria, nitrifying bacteria. 

 

(b) Origin of Photosynthesis : 

After some time bacteriochlrophyll developed in some autotrophic bacteria like organism.

They could absorb solar energy and convert it into chemical form these organism called photoautotrophs.
They utilize solar energy in synthesizing organic compounds. The process is called photosynthesis.

They were anaerobic and utilized hydrogen from sources other than water like H2S.

Therefore, no oxygen was evolved and atmosphere remained reducing .

This stage of photosynthetic autotrophism is represented by planktonic sulphur bacteria of today.

Evolution - Class 12, Biology

 

Oxygen revolution – 

Liberation of free O2 by blue green algae like prokaryotes due to photosynthesis was a revolutionary change in the history of earth. It is called oxygen revolution. 

It includes important changes like –

(1)  Atmosphere of earth changed from reducing to oxidising, hence possibilities of further chemical
evolution and abiogenesis got over, because chemical evolution always take place in reducing environment.

(2)  Free O2 oxidized CH4 and NH3 to form gases like CO2 , N2 and H2O.

(3) Accumulation of free O2 formed a layer of O3 (ozone) above the atmosphere of earth, which started
            absorbing most of the U.V. rays of sunlight.                   

 

Origin of Eukaryotic cell – 

About 2.7 billion years ago conditions become suitable for aerobic respiration with the release of free O2 . Aerobic respiration yields about 20 times more energy then anaerobic respiration hence the prokaryotes adapted themselves for aerobic mode of respiration.

Nucleus, mitochondria and other cell organelles developed in the cell and free living eukaryotic cell like organism originated about 2.0 billion years ago in the primitive ocean.

 

Organic Evolution – 

1. Though life originated by chemical evolution on primitive earth, was later replaced by organic evolution.

2. Organic evolution states ''Descent with modification''. i.e. the present day complex organism have evolved from earlier simpler organism by small but gradual changes which have occurred over millions of years.

3. Though living organisms show diversity in size, structure, function, behaviour etc. they also show basically similar metabolic processes indicating common ancestory. 

 

Points to remember :

1.   Evolution up to formation of coacervates termed as chemical evolution, in which complex organic compound were formed which were essential for formation of cellular structure.

2.   Evolution from coacervates to simple cell structure known as biological evolution.

3.   From simple cell to recent…..evolution is called organic evolution, in which organism developed structures and modified them by which they became more adaptive in their changing environment.  

4.   First protein which is formed during evolution in primitive oceans were not structural.

5.   First nucleic acid which was formed in primitive oceans from combination of nucleotides, did not have power of replication. They obtained power of replication later by mutation.

6.   Evolution term introduced by - Herbert Spencer.

       Evolution - Class 12, Biology

 Evolution - Class 12, Biology

Evolution - Class 12, Biology

Question for Evolution - Class 12, Biology
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What is the term used to describe the process by which complex organic compounds were formed on primitive Earth?
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7.   What is evolution ?

The word evolution  means to unfold or unroll or to reveal hidden potentialities. Evolution simple means an       orderly change from one condition to another.

 

8.   Evolution is a slow but continuous process which never stop-Buffon.

 

9.   Dollo's low – it states that evolution is irreversible.

 

10. Accroding to Theodosius Dobzhansky (1973), nothing in biology makes sense except in the light of
      evolution.

 

11. Scala nature or ladder of nature : – 

Aristotle represented the evolution of complex organism from simple organism in the form of a ladder which is called Scala Nature or Ladder of nature.

He kept simple organism at the bottom of ladder and complex organism at the top of this ladder.

George cuvier studied the evolutionary history of organism by studying fossils and rejected Scala nature.

 

12. The history of life actually comprises two events :

(i)   The origin of life

(ii)  Evolution of life [the mechanism involved in the changes of living organisms through time]  

 

13. Two great themes of evolutionary biology :

(i) The diversity of life, including both the differences and similarities.

(ii) The characteristics of   organism, both adaptive and non-adaptive.

 

14. For origin of life, at least three conditions needed to have been fulfilled.

(i)   There must have been a supply of replicators i.e. self producing molecules.

(ii)  Copying of these replicators must have been subject to error via mutation.

(iii) The system of replicators must have required a perpetual supply of free energy and partial isolation from
the general environment.

 

15. Cosmology–Study of universe.

 

16. Biological evolution is also known as biogeny.

 

17. Unit of evolution is population.

 

18. Oparin's theory also known as primary abiogenesis.

 

19. Evolutionary biology-Study of history of life forms on earth.     

Evolution - Class 12, Biology

 

===============================================================

Evidence of Evolution - Evolution, Biology, Class 12

EVIDENCES OF ORGANIC EVOLUTION 

Some important evidences are – 

 

1.   Palaeontological Evidences – 

 

The study of fossils is known as    :           Palaeontology.

Fossils                                       :           Taken from Fossilis/Fossolium 

Father of palaeontology                 :           Leonard da vinci

Founder of modern palaeontlogy   :           George cuvier

Birbal Sahni is famous for Indian palaeonotology

Two branches of palaentology –

1.   Palaeobotany : Study of plant fossils

2.   Palaeozoology : Study of Animals fossils

Definition of Fossils was given by Charls Lyell ''Impression of past found in Rocks called fossils''

fossils provide one of the most acceptable evidence in support of organic evolution.

Type of Fossils : 

 

1.   Unaltered Fossils : 

In this type whole bodies of extinct organisms are found frozen in ice at the polar regions eg. Wooly
mammoths (25000 yrs before extinct fossils were found from Siberian region)

 

2.   Petrified fossils – Most common type of fossil.

Replacement of organic part by mineral deposits is called petrification.

These fossils consists of only the hard parts e.g. bones, teeth, shells, wood etc. of extinct organisms.

In human body first fossilization occurs of teeth.

Evolution - Class 12, Biology

 

3.   Mould fossils – 

Here no part of the original organism is present, only an impression of the external structure of body is

preserved in wet soil.

 

4.   Cast fossils – 

Sometimes minerals fills in the mould, resulting in cast fossils   

 

5.   Print Fossils – 

Foot print or prints of wings, skin,leaves, stems etc made in soft mud which subsequently become fossilized are a common type of fossils.

 

6.   Coprolites – 

These fossils include the fossil preservation of contents of the intestine or excreta of many ancient

animals including particularly the reptiles or fishes.

 

By studying fossils following facts about organic evolution are evident –

1.   Fossils found in older rocks are of simple type and those found in newer rocks are of complex types.

2.   In the beginning unicellular protozoans were formed from which multicellular animals evolved.

3.   Some fossils represents connecting links between two groups

 

Evolution of Horse – 

Evolution of horse was described by C.marsh.

Evolution - Class 12, Biology

Evolution - Class 12, Biology

The primitive fossil of the horse was   found in North America named Eohippus.

 

Changes during evolution of horse are as follows –

1.   Increase in body height

2.   Increase in the length of neck

3.   Development of high crown on the surface of teeth and formation of cement.

4.   There is gradual increase in the length of  legs.

5.   Number of toes or fingers in legs have reduced in modern horse. Only middle toe touches the ground, other toes reduced gradually.  

6.   Legs become more powerful for fast running

7.   As new species were formed, previous ones becomes extinct.

8.   Enlargement of brain size.

 

Fossils of important Ancestors of horse

1.   Eohippus or Hyracotherium – 

It evolved in Eocene Epoch.

It's size was like a fox.

(Orohippus : It evolved in middle Eocene epoch.)

 

2.   Mesohippus – 

It evolved from eohippus during Oligocene epoch.

It's size was like a sheep. 

(Miohippus : In the late oigocene Mesohippus was replaced by another slightly advanced horse like form named miohippus. It was much like mesohippus in a appearance but some what large in size)

(Parachippus : It evolved in early miocene).

 

3.   Merychippus – 

It evolved in middle and upper miocene epoch. It's size was like a donkey.

 

4.   Pliohippus – 

This horse evolved during pliocene epoch. It was of the size of modern pony.

 

5.   Equus – 

This is modern horse which evolved from pliohippus during pleistocene epoch (height 60-64 inches).

 

''Dating of fossils''  or ''The clock of the Rock''

The fossils give valuable information about the history of organic evolution by giving information about the organisms which existed in the past.

This is possible only if the correct age of the fossils can be determined. Methods have been developed to find out the correct age of the fossils by determining the age of the rocks  where the fossils are found.

Rocks have been found to contain certain radioactive elements which lose their radioactivity and change into other nonradioactive isotopes at a fixed rate irrespective of the environmental conditions prevalling at different times.

If the rate of this loss of radioactivity of an element is known, the relative proportions of the Quantities of radioactive and nonradioactive element in a given rock will enable us to find out the age of the rock.

This method is called absolute dating.

This will be illustrated with the help of four different methods.

(1) Lead method

(2) Radio-carbon method

(3)  Potassium – Argon method

(4)  Electron spin resonance method (ESR method)

 

Geological Time Scale – Firstly given by Giovanni Avduina.

Chronological order of the history of organic evolution, which is presented in the form of geological time scale.

This time scale includes the history of earth itself ever since it was formed to formation of its crust from lava of ancient volcanic eruptions.

The period between the origin of gaseous clould (4.6 billion years ago) from which the earth was formed and the formation of earth's crust is called Azoic Era (era of no life).

The remaining period (about 4.0 billion years) is divided in to five Eras namely –

1.  Archaeozoic                           

2.  Proterozoic                                         

3.  Palaeozoic

4.   Mesozoic                                

5.   Coenozoic

The Archaeozoic Era had ''invisible life'' and the remaining four era had ''visible life'' (Phanerozoic). Archaeozoic and proterozoic eras are also grouped together as Precambrian because the first part of palaeozoic is Cambrian.

The three eras namely palaeozoic, mesozoic and coenozoic, each is further divided into smaller time spans called Period and the periods of coenzoic era are each further subdivided into Epochs.

It is also believed that each era of earth's history started with a revolution or cataclysm and ended with yet another revoluation.

These revolutions meant intense geological disturbances that occurred on earth, so that most of the pre-existing organisms perished in each revolution and the few remaining ones evolved into new and varied organisms.

The first great revolution is believed to have occurred between archaeozoic and proterozoic eras.

The second great revolution between proterozoic and palaeozoic eras.

Applachian revolution between palaeozoic and Mesozoic eras.

Finally the rocky mountain revolution between Mesozoic and coenozoic eras.    

 

Fossils park of India –

1. Birbal sahni institute of palaeobotany, Lucknow.

2. 50 million year old fossil forests preserved in mandla district Madhya Pradesh.

3. 100 million year old fossil forest in rajmahal hills Bihar.

4. 260 milllion year old Coal forming forest in Orissa. 

 

Evolution - Class 12, Biology

Evolution - Class 12, Biology

Evolution - Class 12, Biology

 

Question for Evolution - Class 12, Biology
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Which era is known as the era of no life?
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2.   Morphological and Anatomical Evidences – 

Different animals and plants show dissimilarities in their structure but in some characters they show

similarities. These similarities are of two types.

1.   Homology                 2.            Analogy

 

1.   Homology – 

The similarity based on common origin, similar basic plan of organization and embryonic development is

called homology. 

Similarity in appearance and function is not necessary. 

The organs which have common origin, embryonic development and same basic structure but perform

different functions are called Homolgous organ. Homologous term given by Richard Owen.

 

Examples of Homologous organs –

Evolution - Class 12, Biology

(i)   Forelimbs of mammals – 

                                             Horse                 Bat                   Whale              Seal             Man 

      Appearence                    Foot                    wings               Paddle              Flipper           Hard

      Function                         Running              Flying              Swimming        Swimming         Holding            

In their fore limbs similar bones are present like – humerus, radius, ulna, carplas, metacarpals and
 phalanges.

 

(ii)  Legs of invertebrates – 

Cockroach                     Honey bee

Walking                          Collecting of  pollens

But in both segmented legs are present are segments are same like coxa, Trochanter, Femur, tibia,  1-5 jointed tarsus.  

 

(iii)    Mouth parts of insects 

Cockroach                 Honey Bee                    Mosquito

Biting and chewing      Chewing and lapping      Piercing and sucking

In each of these insects the mouth parts comprise labrum, mandibles and maxillae.

 

(iv) Homology is also seen in the skeleton, heart, blood vessels and excretory system of different vertebrates.

 

(v) Thorn of Bougainvillea and tendril of cucurbita (Modification of axillary bud). 

 

(vi)  Wings of sparrow and pectoral fins of fish.

(vii) Hind limb of mammals.

(viii)  Potato & ginger.

(ix)  Radish & Carrot

(x) Homology is also seen amongst the molecule. This is called molecular homology. For example the proteins found in the blood of man and apes are similar.

(xi)    Testes in male and Ovaries in female develop from same embryonic tissue.

(xii)   Pectoral fin of fish and flipper of seal.

(xiii)  Flipper of penguin (bird ) and dolphin (mammal)

Divergent evolution (adaptive divergence/adaption radiation)   

Evolution - Class 12, Biology

Homology found in different animals indicate their evolution from common ancestors.

Species which have diverged after origin from common ancestor giving rise to new species adapted to new habitats and ways of life is called adaptive radiation, exhibit large number of  homologous organs.

Homology shows Divergent evolution. 

For Example Adaptive radiation gave rise to a varity of marsupials in Australia.         

 

2.   Analogy – 

It is similarity in organs based on similar function.

Organs which have different origin and dissimilar fundamental structure but have similar function are called Analogous organs.

Evolution - Class 12, Biology

Examples of Analogous organs – 

(i)    Wings of bat & birds are analogous to wings of insects.

(ii)    Pelvic fins of fish, flipper of seal

(iii)   Sting of bee and scorpion.

(iv)  Phylloclade of Ruscus and leaf

(v)    Chloragogen cell of pheretima and liver of  vertebrate

(vi)   Hands of man and trunk of elephant

(vii)  Potato and sweet potato.

(viii) Eyes of Octopus and eyes of mammals (different in their retinal position).

(ix)   Dog fish and whale.

 

Convergent evolution (adaptive convergence/parallel evolution)

Development of similar adaptive functional structures in unrelated groups of organisms is called convergent evolution.  

For Example : Some of the marsupials of Australia resemble equivalent placental mammals that live in similar habitats of other continents.    

When adaptive convergence is found in closely related species, it is called parallel evolution.

Analogous organs do not show common ancestory but they show evolution.

Evolution - Class 12, Biology

 

3.   Evidences from vestigial organs –

The organs which are present in reduced form and donot perform  any function in the body but correspond to the fully develop functional organs of related animals are called vestigial organs.

They are remanants of organs which were complete and functional in their ancestors.

Vestigial organs in Human body – 

Human body possess about 180 vestigial organs

eg.  a.   nictitating membrane                                          b.         muscles of pinna (auricular muscles)

      c.   vermiform appendix                                             d.         coccyx

      e.   canine teeth                                                       f.          third molars (wisdom teeth)

      g.   segmental muscles of abdomen                           h.         caecum

      i.    body hairs                                                           j.          nipples in male

      k.   ear pinna                  

 

Vestigial organs in other animals – 

–    Hind limb and pelvic girdle of python

Evolution - Class 12, Biology

–    wings of flightless birds such as ostrich, Emu, Kiwi, Dodo, Reha etc. (Dodo recentely extinct)

–    Eyes of deep sea fishes

–    splint bones in feet of horse [2nd and 4th finger]

–    external ear in whale

–    rudiment of reptilian jaw apparatus.

–    Hindlimb and pelvic girdle of whale.

 

Vestigial organs in plants – 

Scale leaves of Ruscus and various underground steams.

Vestigial organs are example of lamrckism (Theory of inheritance of acquired character) 

 

4.   Evidences from connecting links – 

Some animals and plants possess characters of two separate groups. One being primitive and the other is advanced group.

These species as bridge between two taxonomic groups such organism are called connecting link. They

provide good example of organic evolution of common ancestory.

(i)      Virus : between living and non living

(ii)     Euglena : Between plants and animals

(iii)    Proterospongia : Between protozoa and porifera

(iv)    Neopilina : Between mollusca and annelida

(v)     Peripatus : Between Annelida and arthropoda

(vi)    Archaeopteryx : Between reptiles and birds

(vii)   Balanoglossus : Between nonchordates and chordates

(viii)  Chimera : Between cartilaginous fish and  Boney fish

(ix)    Lung fish (Protopterus) : Between fishes and amphibia

(x)     Platypus : Between reptiles and mammals

(xi)   Echidina : Between reptiles and mammals.

Evolution - Class 12, Biology

 

Question for Evolution - Class 12, Biology
Try yourself:Which of the following organisms serves as a connecting link between reptiles and mammals?
View Solution

5.   Evidences from Atavism (Reversion)  –

Sometimes in some individuals such characters suddenly appears which were supposed to be present in their
ancestors but were lost during the course of development.

This phenomenon is known as atavism or reversion. Atavism proves that animals developing atavistic structure have evolved from such ancestors in which these structures were fully developed.

Evolution - Class 12, Biology

Examples : 

1.   Human baby with tail 

2.   Cervical fistula – in some human babies an aperture is present on neck behind the ear called as
       cervical fistula. It represents pharyngeal gill slits which were present in aquatic vertebrate ancestors. 

3.   Long and pointed canine teeth represented carnivorous ancestors.   

4.   Large and thick body hair reflect our relationship with apes. 

5.   Extra nipples (more than two)       

6.   Evidence from physiology and biochemistry – 

 

Different organism show similarities in physiology and biochemistry. Some clear examples are –

1.   Protoplasm : Structure and chemical composition of protoplasm is same from protozoa to mammalia.

2.   Enzymes : Enzymes perform same function in all animals like Trypsin digest protein from amoeba to man. Amylase digest starch from porifera to mammalia.  

3.   Blood : Chordates show almost same composition of  blood.

4.   ATP : This energy rich molecule is formed for biological oxidation in all animals.

5.   Hormones : Secreted in different vertebrates performs same function.

6.   Hereditary material : Hereditary material is DNA is all organism and its basic structure is same in all
            animals.

7.   Cytochrome C is a respiration protein situated in the mitochondria of all organism. In this protein from
            78-88 A.A. are identical in all organism, which show common ancestory.

 

Physiology and biochemistry thus prove that all animals have evolved from some common ancestor.     

 

7.   Evidences from bio geographical distribution – 

The study of geographical distribution of animal and plant species in different parts of earth is called
Biogeography. 

Different animal species occurring in an area are called Fauna and those of plants are called Flora. 

On the basis of fauna and flora Alfred Russel Wallace divided the whole world into six major biogeographical regions called realms.

Nearctic : North America fro Mexixan highlands to Arctic islands and Greenland.

Palaearctic : Europe, North Asia up to Himalayas and North Africa up to Sahara desert.

Neotropical : Central and South Amerial, Mexican lowlands and West Indies.

Oriental : Asia, South of Himalayas; India, Ceylon, Malay, Peninsula, Sumatra, Bornea, Java Celebes and
      Philippines.

Ethiopian : South Africa from Sahara Desert, Madagascar and Adjacent islands.  

Evolution - Class 12, Biology

Australian : Austrialia, Tasmania, New Guinea, New Zealand and Oceanic islands of the pacific. It is believed that millions of years ago all the continents were present in the form of a single land mass called Pangaea.

Later on due to varies geological changes, these continents drifted fro one another.

As these continents moved away, they got separated from each other by the seas. As these continents had different environmental conditions so plants and animals evolved there were of different varieties. (New species).

 

Palaearctic and oriental realms are separated by high Himalayan Mountains.

1.   Prototheria – 

This is sub class of mammalian, which includes egg laying mammals like Platypus and Echidna found

in Australia.

After the evolution of prototherians from reptiles Australia got seperated from mainland of Asia.

Later on Eutherian mammals evolved in Asia, Due to their carnivorous nature they destroyed prototherians and metatherians from Asia.

So these groups became extinct on the mainland but they survived in Australia due to absence of Eutherians.

Today eutherians are also found in Australia (they were later transported by man).

 

2.   Marsupialia – The subclass of class mammalian includes kangaroos and Opossum which are found only
in Australia.

 

3.   Darwin's finches – Darwin studied Fauna and Flora of Galapagos island situated near south America       (consisted 22 islands). Here he saw 22 types of finches (birds) .

Evolution - Class 12, Biology

A related species of these birds were also present in South American continent.

Probably some member of this species migrated to Galapagos island where these birds evolved into different species as a result of adaptation to environment.

These birds are now known as Darwin's Finches. 

Darwin described that a particular species is evolved in a particular area, progenies of this species migrate to different geographical areas and are gradually adapted to changing environmental conditions.

These adaptations gradually give rise to new species as a result of isolation.

 

Special Point :

a. Darwin's finches are also an example of adaptive radiation (different shape of beak and claws due to their habitat)

b. Darwin's finches are example of allopatric speciation.

 

4.   Elephants and lions are mainly found in Africa and India.

5.   Giraffe, Zebra and hippopotamus are found only in Africa. 

6.   Main land of human evolution in Africa.

 

Important Point : 

Palaeontological and Biogeographical evidences are considered as best evidences in support of organic evolution.  

 

8.   Evidences from Embryology – 

Baer's Law : An organism show its ancestor stages in embryonic development. In embryonic stage general characters appear first then specialized characters appear. 

Muller : First to propose 'Recapitulation theory'.

–    According to it 'ontogeny recapitulate phylogeny' it means any organism show its ancestral adult stages during its embryonic development.

It shows that all organism evolved from a common ancestor.

–    Ernest Haeckel explained it in detail and gave the name 'Biogenetic law'

Examples : - 

(i)   The Zygotes from which the development of all metazoan bodies starts, are single-celled and quite comparable with the Bodies of simple protozoans.

This indicates the origin of Metazoans from Protozoan Ancestors.

Evolution - Class 12, Biology

(ii)     The early stages of Embryonic development, Viz. Morula, Blastula and gastrula are Basically similar in
         all metazoans, indicating a Monophyletic Origin of the latter. 

 

(iii)    The Phylogenetically earliest metazoans i.e., the sponges and cnidarians, have retained early gastrula like double – layered (Diploblastic) structure of Body of Metazoans.

 

(iv)    In fishes,  the young individual, developing from gastrula, is almost-like the adult, but the tadpole larvae
of Amphibians bear more resemblance to the young once of fishes than to their own Adults. This indicates
Origin of Amphibians from fishes.

 

(v)  Even after gastrulation in the vertebrates, the early postgastrula stages are quite similar in members of all
the different classes, Viz, fishes, amphibians, reptiles, birds and mammals.

The differentiation of class characters appear in later stages, moreover, the embryo of phylogenetically
higher vertebrates pass through the adult stages of lower vertebrates before finally attaining the characters of  their respective classes.

This proves that All Vertebrates have evolved from common fish like Ancestors and also that both Birds and mammals have evolved from reptiles.         

 

(vi)    When the heart develops in the embryos of Amphibians, reptiles, Birds and Mammals, it is 2-chambered same as in the embryos and Adults of fishes. In later stages of Embryonic development in Amphibians, reptiles, the heart become, 3-chambered. In Birds and Mammals the heart is 4-chambered in the last embryonic stages to continue as such in the Adults.

 

(vii)   Modern Scientists have discovered ''Biochemical recapitulation'' also.

For example, fishes mainly excrete Ammonia. Adult Amphibians Excrete urea, but their tadpoles excrete Ammonia like the fishes.

Birds excrete uric acid, but their embryos excrete first Ammonia and then urea during earlier stages.

 

(viii)  In embryonic stage birds showed tooth buds for some time, which became extinct later. It show that birds evolved from toothed reptile like ancestors.

 

9.   Evidences from Taxonomy –            

Plants and Animals show a great diversity of form. They also show some similarities among themselves.

It is on account of these differences and resemblances that the taxonomists have to arrange them in to smaller and larger groups.

Amongst species also there are differences and resemblance of varying degree. Some species resemble one another more closely than they resemble others and form a closely related group.

Similarly, there are other groups of closely resembling species.

The members of each group resemble each other more closely than they resemble the members of other groups.

Each such group of species is called a genus. Genera also show different degrees of resemblances amongst themselves.

Those that resembles one another more closely than others are placed in a large group called a family.

Families are grouped in to larger units called orders, orders into classes and classes in to Phyla.

Evolution has a ready explanation for this system of grouping or classifying plants and animals in groups indicates relationship.

 

Special points  : - 

1.   The aquatic mammals [eg. Dolphins, Whales, Seals, Porpoises etc.] don't have gill slits-because their adaptation to aquatic life is secondary.  

 

2.   In Acacia tree well developed compound leaves are found. But seedling has simple leaves like those found in all stages of development of its ancesters. This provide a good example of – Recapitulation

 

3.   Modern day Oaks of southern United State of America retain their foliage throughout  the year where as the oaks of northern United States are deciduous and shed their leaves during water. The southern species, on the basis of this character of leaves are considered to be more primitive than the northern oaks. However, the seedling of northern species are generally seen to retain their leaves during winter. This provide a good example of - Recapitulation

 

4.   EVOLUTIONARY TREND : 

The continuous change of a character within an evolving lineage is termed as evolutionary trend.   

 

THEORIES OF ORGANIC EVOLUTION

lamarckism :

First teory of evolution was proposed by

Jean Bapttiste de Lamarck (17-44 - 1829)

Book : Philosophie Zoologique (1809)

Lamarck coined the terms – Invertebrates, Annelida.

The term Biology was given by Lamarck & Treviranus.

  Evolution - Class 12, Biology

Theory of Inheritance of Acquired Character

 

Basic Concept of Lamarckism–

 

(i)   Internal Vital Forces : 

Some internal forces are present in all organisms. By the presence of these forces organism have the tendency to increase the size of their organs or entire body.

 

(ii)  Effect of environment and new needs:

Environment influences all type of organisms. Changing environment gives rise to new needs. New needs or desires produce new structures and change habit of the organism.

 

(iii) Use and disuse of organs:

If an organ is constantly used, it would be better developed whereas disuse of organ result in its degeneration.

 

(iv) Inheritance of acquired character:

During the life of an organism new character develop due to internal vital forces, effect of environment, new needs and use and disuse of organs.

These acquired character are inherited from one generation to another. By continuous inheritance through many generation these acquired characters tend to make new generation quite different from its Ancestors resulting in the formation of new species.

 

Evolution - Class 12, Biology

 

Example in support of Lamarckism : 

1.   Long neck and high fore limb of Giraffe. 

2.   Aquatic birds stretched their toes and developed web.     

3.   Snakes lost their legs.

4.   Deers became good runners by the development of strong limbs and streamlined body.

5.   Retractile claws of carnivorous animals

 

Criticism of Lamarckism - 

1.   According to first concept organism tends to increase their size but it is not universally true.

For Example among angiosperm the trees seem to be primitive and the shrubs, herbs and grasses have evolved from trees but the size was reduced during evolution.      

 

2.   Second concept is false. Can we sprout wings wishing to fly like birds.

 

3.   The third concept is some what true like the well developed biceps muscles of blacksmith and less developed wings in flight less birds.

But this concept also have many objections like the eyes of a student/reader do not increase in size and power with increasing age, the constantly beating heart maintains a constant size through generation.

 

4.   Fourth concept is completely false because acquired characters are not inherited.

Question for Evolution - Class 12, Biology
Try yourself:
According to Lamarckism, what is the basis for the development of new structures in organisms?
View Solution

–    Weismann –

      Weismann cut off the tails of rats for about 22 genrations but there was no reduction in the size of tail on the basis of this experiment Weismann proposed the theory of continuity of germplasm.    

      According to Weismann.

        (i)    Two types of matters are present in organism, somatoplasm and germplasm.

        (ii)   Sometoplasm in somatic cells and germplasm in Germinal cell.

        (iii)       Somatoplasm dies with the death of organism while germaplasm transfers into the next generation.

        (iv)  If any variation develops in germplasm, it is inherited , while if variation develop in somatoplasm it is not transmitted.

–    Pyane :

      Pyane kept drosophila in dark up to 69 generation, but there was no reduction in the size or sight of eyes

–    Boring of ear and nose in Indians.

–    Iron shoes of Chinese.

 

Neolamarckism-Term by Packard

 

Although Lamarckism remained controversial but some scientists gave the following evidences in favour of Lamarckism. The are known as neo-lamarckians.

 

According to neolamarckism environment effected the inheritance of acquired charater. According to it changing environment give rise some physical and chemical changes in organism, which effect their germplasm, and these acquired characters are definitely inherited.

 

1.   Sumner's Experiment–

Sumner kept white rat in warn temperature resulting in elongation of body, large pinna and long tail. These features were inherited by the offspring.

 

2.   Kammerer's Experiment–

Kammerer kept salamander in dark background. The black spots found on skin were widely spread. In lighter, background the skin became yellow with limited black spots. These character were inherited by the offspring. 

 

3.   Mc Dugal's Experiment-

Mc Dugal trained white rats to cross a tank of water following a definite route. These trained rats were mated and their offspring were again trained. It was observed that there was decrease in the number of errors by offsprings of white rats.

= =======================================================

Charles Robert Drawin was born on 12th feb. 1809 in England. Darwin traveled by H.M.S. Beagle. 

The ship left on Dec. 27, 1831 and returned on Oct. 2, 1836. He travelled South America, South Africa,
 Australia and Galapagos Islands.
Darwin was influenced by two books.

"Principles of population" of Malthus. 

"Principles of Geology" of Charls Lyell.

Evolution - Class 12, Biology

Alfred Russel Wallace :

He travelled South eastern Asia and South America. The idea of natural selection striked in his mind. Wallace wrote an essay and sent it to Darwin. "On the tendency of varieties to indefinitely from original type".

There was striking similarity between the view of Darwin and Wallace.

Wallance's chart :  Wallace presented a chart to explain main points of theory of Darwin:

"Darwinism" or "The theory of Natural Selection" was proposed by both Charles Darwin and A.R. Wallace.

This theory was later on explained by Darwin in his book 'On the origin of species by the means of Natural Selection' (1859).

Evolution - Class 12, Biology

 

The main features of theory of Natural Selection are as follows –

(1)  Over production : (High rate of Reproduction)

All organisms have capability to produce enormous number of offspring, organisms multiply in geometric ratio.

e.g. – Plants produce thousands of seeds.

– Insects lay hundreds of egg

 – One pair elephant gives rise to about six offspring and if all survived in 750 year a single pair would produce about 19 million elephant. Thus some organisms produce more offspring and other produce fewer offspring This is called differential reproduction.

 

(2)  Struggle for existence :

Every individual competes with other of the same and other species for basic necessities like. Space, shelther and food. It is called struggle for existence and it continues for the whole life from zygote stage to its natural death.

     

(3)  Variations and heredity :

Exept identical twins no two individuals are similar and their requirements are also not same.It mean there are differences among the individuals. These differences are called variations.

Due to variations some individuals would be better adjusted towards the surroundings than the others.

According to Darwin the variations are continuous and those which are helpful in the adaptation of an organism towards its surroundings would be passed on to the next generation, while the others will disappear.

 

(4)  Suvival of the fittest or natural selection :

The original idea of survival of fittest was proposed by Herbert Spencer.

According to Darwin most suitable and fit individuals are successful in struggle for existence.

The individuals with most favourable adaptations are able to lead most successful life and are able to win over their mating partners.

Darwin called it Sexual Selection.

In the struggle for existence only those members survive which posses useful variations means nature selects fit individuals.

This was called Natural Selection.

Fitness is the end result of the ability to adapt and get selected by nature.

 

(5)  Origin of New Species :

Darwin explained that variations appearing due to environmental changes are transmitted to the next generation.

So offspring become different from ancestors. In nest generation process of Natural selection repeats so after many generation a new species is formed.

 

Criticism of Darwinism –

1.   Darwin does not explain the development of vestigial organs.

2.   No satisfactory explanation for the cause, origin and inheritance of variation.

3.   Darwin is unable to explain why in a population only a few individuals develop useful variation and others have harmful variations.

4.   Criticism of Darwinism was based on sexual selection. Why only female selects the male for mating why not vice versa.

5.   Darwin was unable to differentiate between somatic and germinal variations.

6.   This theory was unable to explain over-specialization of some organs like tusk of elephants, antelers of deer.

7.   This theory only explain the survival of fittest but unable to explain arrival of fittest.

8.   The main drawback of Darwinism was lack of the knowledge of heredity

 

Theory of pangenesis

According to this theory all organs of an individual produce Pangenes, which are minute particles carrying information about the organs.

The pangenes traveling through the blood stream will ultimately reach the gametes, so that each gamete will have pangenes for each of the different organs.

After zygote formation, the pangenes tend to form the same organs from which these pangenes were produced.

 

NEODARWINISM : 

NeoDarwinism is a modified form of Darwinism along with recent researches of Weismann, Mendel,
 DeVries, Huxley, Gates, Stabbins
ets. They performed many experiments to remove the objections against Darwin's theory.

 

The salient features of neodarwinism are as follows–

1.   Rapid multiplication : All organism multiply in geometrical ratio.

2.   Limited food and space : Food and space are limited.

3.   Struggle for existence : It is of three types. Intraspecific, Interspecific and environmental.

      The struggle for existence is of three types –

      (i) Intra-specific struggle : It is competition between the individuals of same species for same needs like food, shelter and breeding (most acqute type of struggle).

      (ii) Inter-specific struggle : It is the struggle between the individuals of different species for food and shelter.

 

(iii) Environmental struggle : This struggle is between the organism and their environment. All organism struggle with cold, heat, wind, rain drought and flood etc.

 

4.   Genetic Variations : They are inheritable variation which can occur due to the following reasons.

(a)  Mutation : They are discontinuous variations which develop due to permanent changes in genotype. Mutations are of three types –

          Genomatic mutations : Change in number of chromosome.

                      Chromosomal Aberrations : Changes in number of chromosome.

                      Gene Mutation : Change in nucleotide.

(b)  Gene recombination : They are new combination of genes which are usually caused by crossing over.

(c)  Hybridisation and gene migration : It is crossing of organisms which are genetically different in one or more traits.

(d)  Random Genetic drift : It is the elimination or addition of the genes of certain chartain characters when some animals in population migrate or dies or immigrate. It changes the gene frequency of remain population. Genetic drift operates only in small population.

(Changes in frequency of genes in a gene pool is called drift)

Founder Effect :    Gene pool is the sum total of all the genes found in a population.

Change in the frequency of gene in a gene pool is called genetic drift.

Genetic drift always operates in small population.

By genetic drift often the phenotype of this small population quickly become different from the parental population and some time form a new sp. Such an effect is called Founder Effect.

Bottleneck Effect : Death of several members of population due to natural calamities (Earthquake , Storm, Flood) also leads to genetic drift.

The original size of population is then restored by mating among the survivor.

The new population may lack the genes of certain.

This may produce a new species after some time.

The loss of a section of population by death an after sometime a new species is formed that effect is known as Bottleneck effect.

 

5. Natural Selection :

If differential reproduction (some individuals produce more, some only few and still others none) continue for many generations, genes of the individuals which produce more offspring will become predominant in the gene pool of the population.

Thus natural selection occurs through differential reproduction in successive generations. 

 

6.   Isolation :

Isolation is a segregation of populations by some barriers which prevent interbreeding.  The reproductive isolation between the populations due to certain barriers leads to the formation of new species.

 

Example of Natural Selection –

(1)  Industrial Melanism : 

This phenomenon was studied by Barnard kettlewell. 

Evolution - Class 12, Biology

Before industrial revolution, the dull grey forms of prepared moth-Biston betularia – were dominant; the Carbonaria form (Black) was rare because it was susceptible to predation by birds.

The industrial revolution, resulted in large scale smoke which got deposited on tree trunks tuning them Black. Now grey varieties became susceptible – the black forms flourished.

Replacement of coal by oil and Electricity reduced production of black moth so the frequency of grey moths increased again.

 

(2)  Drug resistance :

The drugs which eliminate pathogens become ineffective in the course of time because those individuals of pathogenic species which can tolerate them, survive, flourish to produce tolerant population.

 

(3)  Sickle cell Anaemia and Malaria : 

Individuals homozygous for sickle cell Anaemia die at an early age.

In heterozygous individuals, the cells containing abnormal haemoglobin Sickle shaped.

In fact, When an RBC becomes sickle-shaped, it kills Malarial parasite effectively so that these individual area able to cope with malaria infection much better than normal persons.

The processs of natural selection thus maintains the abnormal form of haemoglobin along with the normal form in a region where Malaria is common.

 

(4)  Malaria and G-6-PD deficiency :

Glucose 6- Phosphate dehydrogenase deficiency  is a common abnormality in Negroids. Haemoglobin gets denatured and is deposited on cell membrane.

The disease is called favism. In these RBC, the malarial parasite cannot complete It's cycle.

Such persons get protection from Malaria.

Question for Evolution - Class 12, Biology
Try yourself:
What is an example of natural selection mentioned in the passage?
View Solution

Artificial Selection – 

Man has been taking the advantage of genetic variations for improving the qualities of domesticated plants and animals.

He selects the individuals with desired characters and separates them from those which do not have such characters. The selected individuals are interbred.

This process is termed as Artificial Selection. This process is man made.

If it is represented for many generations it produces a new breed with desired characters.

By artificial selection animal breeders are able to produce improved varieties of domestic animals like dogs, horse, pigeons,, poultry, cow, goats, sheep and pigs from their wild ancestors. Similarly

Evolution - Class 12, Biology

the plan breeders have obtained improved varieties of useful plants like wheat, rice, sugarcane, cotton, pulses vegetables fruits etc.

Artificial Selection is similar to natural selection except that the role of nature is taken over by man and the character selected are of human use.

The breeders have successfully produced the toy-like Shetland pony, the Dane dog, the sleek Arabian race horse by selection.

Many crop plants like broccoli, kale cabbage, Cauliflower, Brussels sprouts and kohirabi have been produced through selective breeding.

The various breeds of fowl ranging from the ceremonial cocks (the Japanese onago-dori) to the broiler. leghorns are all derived from a single jungle fowl Gallus gallus.

 

Reproductive Isolation – 

Reproductive isolation is the prevention of inter breeding between the population of two different or closely related species.

It maintains the characters of the species but can lead to the origin of new species.

The mechanism the characters of the species but can lead to the origin of new species.

The mechanism of reproductive isolation is explained by Stebbins in his book 'Process of Organic Evolution'.

 

Two main subtypes of reproductive isolation are– 

1.  Premating or prezytotic isolation : 

Prevent matting or formation of zygote.

      (1)  Ecological isolation : Two species live in different habitats and do not meet. (One may be living in fresh water and the other in the sea).           

      (2)  Temporal isolation : Breeding seasons or flowering time may be different in the two species.         

      (3)  Behavioural isolation :  The males of one animal species are unable to recognize the females of another species as potential mates.

      (4)  Machanical isolation : The structural differences in genitalia of individuals belongings to different animal species interfere with mating.

      (5)  Gametic isolation : The sperms and ova of different species of animals are unable to fuse. In plants, the pollen coming from a different species may be rejected by the stigma.

 

2.   Postzygotic Isolation  : A hybrid zygote is formed but it may not develop into a viable fertile adult.

(1) Hybrid inviability : Hybrid zygotes fail to develop. In plants, embryos arising from interspecific crosses abort.

(2)  Hybrid sterlity : Hybrid adults do not produce functional gametes. (Mules and henny are common example) in mammals. Several hybrid ornamental plants are sterile.

Evolution - Class 12, Biology

3.   Hybrid breakdown  : Sometime inter specific mating produce a hybrid, which give rise to next hybrid by back cross but they have reduced vigour or fertility or both.

 

GENETIC BASIS OF ADAPTATIONS :

Joshua Lederberg  & Esther Lederberg  shown genetic basis of adaptations by experimenting on bacteria. This experiment is known as Ledeberg's Replica plate experiment.

1.    Lederberg cultured the bacterial cells on agar plate.

      Many bacterial colonies or groups grew on this agar plate.

      In this every colony is formed  by the division of bacterial cells.

      Therefore its all cells were of same genetic structure.

     This type of group of cells is known as clone.

      This multi colony agar plate is known as master plate.

    

2.   On this master plate one sterile velvet plate was pressed slightly so that some bacteria got stuck on velvet plate. In this way this becomes replica of master plate. 

Evolution - Class 12, Biology

 

3.   Now efforts of preparing replica had been made on those agar plates whose agar contains an antibiotic penicillin. It was seen that some bacteria failed to grow on penicillin agar plate while some bacteria were able to grow and developed new colony.

It was concluded that these bacterial colonies were penicillin resistant.

These bacteria have penicillin resistant mutant gene.

* Lamarckian view : Penicillin induced a change in some bacterial cells enabling them to grow in medium containing penicillin (wrong concept).

** According to Darwin some bacterias were penicillin resistant in bacterial suspension. In penicillin medium normal bacteria did not survive while mutant bacterias survived, as they are adapted, and form colony.

============================================================

MODERN SYNTHETIC THEORY OF ORGANIC EVOLUTION - Evolution, Biology, Class 12 

MODERN SYNTHETIC THEORY OF ORGANIC EVOLUTION  : 

This theory is the result of the work of a number of scientist namely Dobzhansky, Fisher, Haldane, Swall wright, Mayr, Stebbins. 

Stebbins discussed this theory in his book ''Process of Organic Evolution'' and Dobzhansky explained it is his book ''Genetics and the origin of species''.

According to this theory new species can not evolved by the presence of variable genotype in  a population. Two factors are also required-natural selection and reproductive isolation.

Natural selection guides different population in to different adaption direction and reproductive isolation between them due to geographical barriers leads these direction to the evolution of new species.

In this theory following factors are included  –

(i)   Gene mutation

(ii)  change in chromosome number and structure

(iii) Genetic recombination

(iv) Natural selection

(v)  Reproductive isolation.

Besides these factors there are two more processes which cause evolutionary changes. These are –

      (i)   Migration of individuals from one population to another.

      (ii)    Hybridisation among species and also related genera which causes genetic variation in the population  undergoing process of evolution.

 

Mutation Theory

Proposed by Hugo-de-vries on the basis of his experiments on a plant Oenothera lamarckiana.   

 

Main Point of mutation theory : 

1.   Mutation or discontinuous variation are the raw material of evolution.

2.   Mutation appears suddenly and produced their effect immediately.

3.   Mutants are different from the parents and there are no intermediate stages between the two.

4.   The same type of mutation can appear in several individuals of a species.

5.   Mutation can appear in all direction and all mutations are inheritable.

6.   useful mutations are selected by nature and lethal mutations are eliminated.

7.   Mutation are recurring so that the same mutant can appear again & again so change of selection by nature are increased and new species is formed.

8.   De-vries termed single step large mutation as saltation.

9.   Mutations are large, random and directionless while Darwinism variations are small and directional.

 

Points in favour of mutation theory : 

1.   Mutations are actually the source of all variations and fountainhead of evolution.

2.   Mutation theory can explain both progressive & retrogressive evolution.

 

Significance : 

De-vries mutation theory generally accepted because the mutation were found to be inheritable. It was later through that evolution cannot occur by mutation alone, natural selection and isolation of mutants are also necessary for evolution.

 

Natural Selection & Polymorphism : 

A population is called polymorphic for a character if two or more distinct form are present in this population.

 

Ex.: ABO Blood Group :

There are 4 types of blood group are present in human being A, B, AB. and O. They are due to the presence
of different genotype.

Sickle cell anemia is also an example of polymorphism. In this disease on amino acid is changed in
polypeptide chain due to change in one N2 base. That's why the normal shape of RBC is changed into sickle
shape.

The organism in which heterozygous condition is present for this characters, the RBC become sickle shaped.
In this type of RBC malarial parasite can't have a normal growth that's why these individuals are resistant
towards malaria.

The HbS, HbS, condition leads to the death of organism.

The organism with HbS, HbA condition are selected by nature because these are the fittest of all. The lose of HbS gene due to the death of organism having HbS, HbS is recovered & balanced by the reproduction of
heterozygous condition (HbS, HbA).

This type of selection is called balancing selection.

It means the  preservation of genetic variability is maintained by the selection of hertozygotes which is called
'Balanced polymorphism'.

But this kind of balancing selection is found very rarely in nature.

 

Types of Natural Selection :

Evolution - Class 12, Biology

Based upon different organism – environment relationship. Following different kinds of natural selection
have been recognised.

–    Stabilising selection.

–    Directional selection.

–    Disruptive selection.

 

(1)  Stabilising selection : 

Stabilizing selection operates when phenotypic feature coincide with optimum environmental conditions and competition is not present.

It keeps a population genetically constant.

It favours the average or normal phenotypes and eliminate the extreme variants, that fall towards both ends of the bell-shaped curve of variability for the distribution of measurements of phenotypic traits.

Due to continuous elimination of both extremes, the bell shaped curve tends to narrow.

Stabilising selection always operates in constant or unchanging environment.

Ex. Mortality in babies : The birth weight of human babies provides another example influenced by stabilizing selection.

The optimum birth weight favoured by stabilizing selection is 7.3 pounds.

New born infants less than 5.5 pounds and more than 10 pounds have the highest mortality rate. The curve for mortality is virtually the complement of the curve of survival.      

 

Evolution - Class 12, Biology

 

(2)  Directional selection or Progressive selection : 

Directional selection produce a regular change in a population in respect to certain traits.

This form of selection operates in response to gradual changes in environmental condition.

It favour the phenotype which is non average or extreme and then pushes the phenotype of the population in that direction.

Directional selection removes more individuals from one end of the normal curve of variability distribution and adds towards the other end and alters the mean value of the trait in the population in a particular direction.

So the mean moves in one direction.

Directional selection operates when environment is changing in one direction.

Ex. (1) Biston betularia

      (2)  Resistance of insects to DDT.  

 

(3)  Disruptive selection : 

This is probably the rarest form of selection but can be very important in bringing about evolutionary change.

Presence of more than one phenotype in a population.

Selection pressure acting from within the population as a result increased competition may push the phenotype away from the population mean towards the extremes of the population.

This can split a population into two subpopulation.

If the gene flow between the subpopulation is prevented, each population may give rise to a new species. In
some cases this form of selection can give rise to the appearance of different phenotype within a population,
known as polymorphism.

Question for Evolution - Class 12, Biology
Try yourself:
Which type of natural selection occurs when the phenotype of a population moves in a particular direction due to gradual changes in the environment?
View Solution

 

Eg. Shell pattern in limpets : Shell patterns of limpets (marine mollusca) present a continuous, ranging from pure white to dark tan. These are either attached to white goose neck barnacles or to tan-coloured rocks. The white or light-coloured limpets camouflaged withy white barnacles and tanned ones were protected on the tan-coloured rocks. Limpets of intermediate shell patterns, being conspicuous are preyed by predatory shore birds, resulting in distruptive selection.

===================================================================

Speciation - Evolution, Biology, Class 12

Speciation

Formation of one or more new species from an existing species is called speciation. Speciation are of 2
types.

A.  DIVERGENT SPECIATION : Origin of one or more new species from an ancestor species is called
divergent speciation.

In this type of speciation ancestor sp. also continuous to exist with new species.

In this type of speciation no. of species are increased.

Divergent speciation are of two types –

 

(1)  Allopatric Speciation : When a species split into two or more geographically isolated population and these population finally form a new species.

This mode of speciation is called allopatric speciation and these sp. are known as allopartic species.

Ex. : Finches of Darwin are example of Allopatric speciation.

 

(2) Sympatric species : In this type of speciation a sub population becomes reproductively isolated from its
parental population.

Sympatric speciation is the formation of species without geographical isolation and these sp. are known as
sympatric species.

B.   Transformation speciation : in this type of speciation an ancestor species change into a new sp. with time. In this process no. of species is not increased.

Transformation speciation are of two types –

 

(1)  Phyletic Evolution : When an ancestor sp. changed in to a new species by gradual change in thousand of
years.

e.g. Eohippus → Mesohippus → Merychippus → Pliohippus → equus

 

(2)  Quantum Species : In this process suddenly major changes appears in ancestor species and ancestor species immediately changed into new sp. No. connective links are present in this type of speciation. It is caused by major mutation.

 

Special point : 

Micro evolution : - Micro evolution is the occurrence of small-scale changes in gene frequencies in a
population, over a few generations.

It occurs at or below the species level. It often cause the formation of new subspecies.

These changes may be due to several process-Natural selection, gene flow. mutation, recombination, genetic
drift etc.

eg. Formation of clines.     

 

Macro evolution : - Macro evolution is the evolution, which results in the production of new adaptive types through a process of population fragmentation and genetic divergence.

It is the occurrence of large-scale changes in gene frequencies in a population, over a geological time period (consisting of lots of micro evolution).

Macro evolution operates above the species level and results in the establishment of new genera, families and order.

The changes in the organization occurs due to accumulation of large mutation (macro mutation).

The divergent evolution of different reptilian group from initial reptile ancestor is example of macro evolution.

 

Mega evolution : - The origin and evolution of new types of biological organization as a result of general adaptation  from its predecessor  resulting in the formation of new classes, phylum.

Mega evolutionary changes are rare and have occurred only a few times in the evolutionary history of living beings.

Ex. Origin of Amphibia from fishes, origin of reptiles from amphibian, origin of bird and mammal from reptile.

 

Anagenesis : - It is the evolution of species involving a change in gene frequency in an entire population. It
is also known as phyletic change. Anagenesis may also be reffered to as phyletic species or gradual species.

 

Cladogenesis : - It is an evolutionary splitting event in which each branch and it's smaller branches form a '      clade' an evolutionary mechanism and a process of adaptive evolution that leads to the development of a
greater variety of sister organism.

=========================================================

Evolution of Man - Evolution, Biology, Class 12 

HUMAN EVOLUTION

The primates include Prosimians (Lemurs, tarsiers and related forms) and Anthropoids (Monkeys, apes and Human). They are descended from small rodent like or insectivorous mammals that evolved about 80 million years ago.

Evolution - Class 12, Biology

Evolution - Class 12, Biology Order primata is divided into 2 sub orders.

Evolution - Class 12, Biology

Monkeys : - 2 types

 

(1)  Old world monkeys : - Rhesus (Macaca), Baboon (Old world = Africa. Asia)

      (1)  Tail, non prehensile tail.

      (2)  Narrow flat nose with downward direction of nostril.

      (3)  U-shaped Jaw.

      (4)  Dental formula same as human

      (5)  Menstruation cycle is present in female.

(2)  New world monkeys : - spider monkey, marmosets (New world = South & Middle America)

      (1)  Long, prehensile tail

      (2)  Protruding nose with upward direction of nostril

      (3)  U-shaped jaw

      (4)  Dental formula

      (5)  Menstruation cycle absent but estrous cycle is present.

      So, Old world monkeys are more closer to human. 

Evolution - Class 12, Biology

Human - Hominideae Family 

 

Similarities between man and apes : - 

(1) Tail absent

(2)  Erect posture

(3)  Grasping hands       

(4)  Hairs are present on body

(5)  Larger head, more cranial capacity

(6)  More intelligent than other animals    

(7)  Facial muscles are present for expression of surprise, pleasure.

(8)  Menstruation cycle is present in female of both

(9)  Blood group of AB series are present in both.           

(10) Composition of Hb is same in both. Only one amino acid is different in human and Gorilla. 

(11)  Chromosomal similarities : - 

(i)   No. of chromosomes are approximately same in man and apes.

Apes =  48

Man = 46

 

(ii)  DNA contents and DNA matching is same in both. This similarity is

100% with Chimpanzee

94% with Gibbon

88% with Rhesus monkey

     

(iii) Banding pattern of chromosome is same in both.

Comparisons have been made between banding pattern of  chromosomes of man and those of the great apes.

                            

Banding pattern of ch. no. 3, 6 of human and chimpanzee is 100% similar.

Banding techniques enable the identification of individual chromosomes and their parts.

Somatic cells of human contain 46 chromosomes (44 Autosomes and 2-sex chromosomes).

The diploid number of chromosomes in Gorilla, chimpanzee and Oranguttan is 48.

⇒  The total amount of DNA in human diploid cells and that of the great apes are dissimilar.

⇒Similarity in the fine structural organization of the chromosomes is understood only in terms of a common origin for man and chimpanzee.

Evolution - Class 12, Biology

Differences : -

Evolution - Class 12, Biology

 

Human evolution :

      (1)  Propliopithecus : - Origin & evolution in Oligocene epoch so called as Oligocene apes. Evolution
            about 30-35 million years ago.

      (2)  Aegyptopithecus : - Origin and evolution in late Oligocene and Miocene epoch so called as Miocene
            apes.

     (3) Proconsul : - Its fossils were discovered by Leakey from East Africa near Victoria lake in Kenya
           from Miocene rocks. It walked on its four legs (considered as common ancestor of man and apes).

      (4)  Dryopithecus : - Evolution » 15-20 million years ago.

      –    Direct ancestor of modern day apes.

      –    They were forest dwellers spending most of the time one the trees.

      –    Origin & evolution in Miocene epoch.

      –    Semi erect posture

      –    Quadra pedal locomotion, forlimbs longer than hind limbs.

      –    Thick growth of  hair

      –    U shaped jaws

      –    Teeth larger and sharper

      –   By nature vegetarian, fruit eater

Evolution - Class 12, Biology

–    Origin and evolution in Pliocene epoch.

     

      –     They are considered as ancestors of human but in characteristics same as Dryopithecus, but   
    spending most of the time on the land.

 

(8)  Australopithecus :- Prof. Raymond dart discovered a fossil of skull of 5-6 year old baby from the old Pliocene rocks of  Tuang region (S. Africa). He named it Tuang baby, later on he renamed it A. africanus.

–    About 3-2 million years ago it lived in East African grasslands.

–    Evidences shows they hunted with stone. Probably ate fruits.

–     It was an apeman because it have many characters of man and apes so it is also considered as

        connecting link between apes and man.

 

Apes like characters : 

–    Less cranial capacity – 400 – 500 c.c.

–    Thick growth of hair on body

–    Prognathous.

 

Man like characters : 

–    Complete erect posture (first man who stood erect)

–    Forelimb shorter than hindlimbs.

–    Bipedal locomotion (first man)

–    Some other varities of Australopithecus were also discovered by some other scientist.

–    A. boisei [zinjanthropus] by Leakey from East Africa [Tanzania]

–    A. afaransis [Lucy] by Donald Johanson from Ethiopea.

 

Prehistoric man : - 

A number of other species of Homo appeared and became extinct from time on the evolutionary sense before the origin of homosapiens. These extinct species are called prehistoric species of man. 

(1) Homo habilis : - The Tool maker or Handy man.

–    First human being like

–    By nature omnivorous, also show cannibalism

 

(2) Homo erectus : - direct ancestor of homo sapiens

Evolution - Class 12, Biology

–    Origin and evolution, 1.5 million years ago.

–    Java man

–    Peking man

–    Heidelberg man (Branch from main line of Human evolution)

     

Java man :

Homo erectus erectus name given by Mayer. 

or  Pithecanthropus erectus given by Dubois.    

–    Fossil obtain from central java by Eugene Dubois.

–    Lived in caves

–    They used Tools of bones and stones

–    Cranial capacity – 900 c.c.

    First man who used fire for hunting, protection and cooking 

–    Chin absent, Jaw Prognathous

–    Complete erect posture

–    Omnivorous, cannibalism have also found.

–    It is also known as erect ape man

Peking man : - Homo erectus pekinensis name given by Mayer 

Sinanthropus erectus name was given by Davidson Black  

Evolution - Class 12, Biology

–    W.C. Pai discovered the fossil of peking man from China.

–    Lived in caves

–    Cranial capacity – 1100 c.c.

–    Chin absent, Jaw Prognathous

–    Used sharp chisel shaped tools of stones, bones for cutting and killing animals.

–    Omnivorous, cannibalism has been also found

–    Used fire for cooking meat and for protection.

 

Heidelberg man : - 

A fossil of lower jaw obtain from Heidelberg in germany it was discovered by Ottoschotensack.

–    Cranial capacity – 1300 c.c.

–    Origin & evolution – in Pleistocene epoch. It is believed that this species was evolved as a branch from main line of evolution and got extinct after some time

 

(3) Homo sapiens : - 

–    Neanderthal man

–    Cromagnon man  - Direct ancestor of modern man

–    Homo sapiens sapiens - Modern man (Man of today)  

(i)   Neanderthal man : - Homo sapiens neanderthalensis

–    Origin  & evolution before a 30,000 – 1 lakh years

Fossils were discovered by C. fulhrott from Neanderthal vally of Germany.

–    They live in huts.

–    Cranial capacity 1400 c.c

Complete erect posture

Ceremonial burial of dead body

Used animals skin as cloths

Beginning of development of speech center.

By nature – omnivorous.

–    First man believed in ''immortality of soul''

Evolution - Class 12, Biology

 

(ii)  Cromagnon man : - Homo sapiens fossils

–    Origin and evolution 34000 years ago.

–    Fossils discovered from Cromagnon rocks of France

–    Lived in caves

–    Cranial capacity - 1650 c.c. (maximum) 

–    Complete erect posture

–    Well developed speech centre

–    Orthognathous jaw.

–    Used animal skin as cloth.

–    This man was hunter and used domesticated dogs in hunting, so domestication of animals started
       by cromagnon man.

–    Known for cave paintings.

–    Regarded as the direct ancestor of modern man.

–    By nature carnivorous.

Evolution - Class 12, Biology

 

(iii) Homo sapiens sapiens (Modern man) : - Man of today

–    10,000  years ago.

–    Cranial capacity 1450 cc  

–    Complete erect body posture

–    Orthognathous

–    Well developed speech centre, developed languages.

–    Less hairs on body as compared to fossil man

–    Omnivorous.

–    It is believed that modern man evolved in Africa.

–    Agriculture was also started by them. 

     

Question for Evolution - Class 12, Biology
Try yourself:
What is the estimated age of the origin and evolution of Propliopithecus?
View Solution

Special Point :

The course of cultural evolution is divided in to three age.

Palaeolithic           –    Age of tools of stones and bones.

Mesolithic             –    Age of animals husbandry, language, reading, writing.

Neolithic

(i)   Bronze age          Age of agriculture, knowledge and use of clothes.

(ii)  Iron age              Present age is also known as Iron age.

 

Man of future : - homo sapiens futuralis

–    Dr. Shapiro named man of future as Homo futuralis    

–    Taller and hairless body          

–    Tomb like head and larger brain.

–    With no fifth finger

 

      Special Point : - 

      (1)  Anthropology :- Study of evolutionary history of man.

      (2)  Ethology : - Study of animal babbits and behaviour.

      (3)  Hylobates hoolock :- (The Gibbon) is the only ape found in India (forests of Assam)

      (4)  Races of human - 4 types - Caucasoid, Negroid, Mongoloid, Australoid.

      (5)  Hobit : - Recently Rechard Roberts scientist discovered a 18,000 years old fossil of a lady form flors

            island situated near Australia. He gave name it to Hobit/Dwarf man/Homo florasiansis.

 

Evolution - Class 12, Biology

Evolution - Class 12, Biology

BRIEF REVIEW

Evolution - Class 12, Biology

–    Tree shrews were first real primates.

–    Old world monkeys are more closer to human as compared to new world monkeys.

–    Chimpanzee is closest ape to human.

–    Australopithecus firstly show bipedal locomotion.

–    Homohabilis is also known as handy man or the tool maker man.

–    Java man firstly used fire.

–    W.C. Pai discovered the fossils of Peking man from China.

–    Neanderthal man was first man who believed in 'immortality of soul.'

–    Cromagnon man was a painter and regarded s the direct ancestor of modern man.

–    Homosapiens sapiens is the man of today.

–    Carolus Linnaeus called human as Homo sapiens wiseman. 

–    Huxley explained origin of man in his book  The man's place in nature'.

–    Darwin explained ancestory of man in his book 'The descent of man'. 

–    Human is a member of order primatas of class mammalia.

–    Primates originated 80-100 million years ago in palaeocene epoch of  coenozoic era.

–    Primates originated from elephant shrews but they were not real primates.

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FAQs on Evolution - Class 12, Biology

1. What is evolution?
Ans. Evolution is the process by which living organisms adapt and change over time due to changes in their environment or genetic makeup. This process occurs through natural selection, genetic drift, mutation, and gene flow.
2. How does natural selection contribute to evolution?
Ans. Natural selection is the process by which organisms with advantageous traits are more likely to survive and reproduce, passing on those advantageous traits to their offspring. Over time, this can lead to the development of new species and the evolution of existing species.
3. How is genetic drift different from natural selection?
Ans. Genetic drift is the random fluctuation of gene frequencies in a population over time. This can occur due to chance events, such as a natural disaster that reduces the size of a population. Unlike natural selection, genetic drift does not necessarily favor traits that are advantageous for survival.
4. Can evolution occur without natural selection?
Ans. Yes, evolution can occur without natural selection. Other mechanisms of evolution, such as genetic drift, mutation, and gene flow, can also lead to changes in the genetic makeup of a population over time.
5. What is the evidence for evolution?
Ans. There is a wide range of evidence for evolution, including the fossil record, comparative anatomy and embryology, molecular biology, and observations of natural selection in action. These different lines of evidence all support the idea that living organisms have changed and adapted over time through the process of evolution.
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