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Evolution The term evolution literally means unrolling or unfolding or opening out.basically evolution is a process of change or transformation. Evolution is the development of living things in the passage of time it’s not a science. It is not a science but concept. evolution to be more precise is the gradual development from the simple unorganized conditions of the primal matter to the complex structure of the physical universe and the origin of life; and in a similar manner from the beginning of life on this habitable planet to a gradual unfolding and diverstigation into the varied forms of beings which constitute the animal and plant kingdom. The former is termed inorganic evolution and later organic evolution.bilologist interprets thehistory of plants and animals on this earth to have been under going such process of gradual change which produced the existing species.the orgin of existing organism from ancestral types is called organic evolution.the theory of organic evolution is the scientific explanation of how the present day complex forms of plants and animals have evolved from the simpler ancestors of past by a process of gradual change.many scientist says their own idea on evolution. The first this word was used by Herbert spencer on English philosopher.the main p[oints on evolution was put forward by charles Darwin who studies for long period and he wrote a book called origin of species which is considerd as the world classics.he defined evolution as descent with modification. Origin of life Theories on the origin of life The major theories accounting on the origin of life on earth are 1.	The Theory of special creation 2.	The Theory of spontaneous generation 3.	The Steady state theory 4.	The Cosmozooic theory 5.	The theory of inorganic evolution Theory of special creation This theory supported by worlds major religions and civilizations and attributes the origin of life to supernatural event at a particular time in the past. Theory of spontaneous generation This theory is also known as theory of abiogenesis.it was found by Aristotle. Aristotle and other philosophers of ancient and even up to 16th century believed in abiogenesis. It seemed obvious from Aristotle’s casual observations that maggots were naturally produced by meat left out in the open- and muddy puddles of water could bring forth living. On the basis of his personal observations. In relating all organism to a continual ‘scala natura’. An Italian physician Francis Coreddy was the first who give experimental evidence for to break spontaneous generation. He said flies are not spontaneously generated by meat it self but rather by adult flies that lay eggs on protected meat. Evidences against this spontaneous generation of micro organisms were provided in 1860 by series of elegant experiment by loui paster. Cosmozoic theory Life originates else were in the universe and travel through the space and colonized in the earth .this theory is known as Cosmozoic theory. The theory of inorganic evolution This theory is also known as theory of chemical evolution or oparin haldin theory. The idea of materialistic origin of living system was revived in 1936 by a Russian biochemist Alexander oparin in his book origin of life on earth. The same idea was also elaborated by J B S haldin in 1928 independently and hence it is also called oparin haldin theory. Oparin called attention to the fact that the environmental condition on earth are quite different when living systems are being formed the atmosphere at that time is rich in reducing gases ,a such as ammonia, methane, hydrogen, and water vapour rather than predominantly of oxygen and nitrogen as present today. If free oxygen would have been present as seen today the organic compounds first formed would have been oxidized away. Oparin proposed the organic compound from which contemporary life is built where produced by energy of sunlight, electrical discharges and volcanic heat acting on the components of the primitive atmosphere. He also opine that this early organic molecules might have accumulated to tiny droplets called coacervates. These droplets represent open systems that passively concentrate materials from their environment. Oparins hypothesis weighted almost 30 years for experimental conformation. In 1953 Standly Miller student of Harold C Urey subjected four gases namely hydrogen, methane, ammonia and water vapour to the energy of an electric spark and so heated the mixture through a boiling water bath. The stem condensed in to water and flow in to a U tube at the base of the apparatus and then in to the small flask containing boiling water thus promoting circulation in one direction. The various gases formed the atmosphere and water the ocean this electric discharge simulated lightning, while a heating coil get the water bubbling. The experiment conduct continuously for a week and fluid in the flask was analyzed. Diagram of miller Urey experiment Diagram of the miller apparatus which was used to produce organic molecules under conditions similar to those found on earth. With in a few days the water and glass were stained with reddish gloo on analyzing the substance miller found to his delied that it was reach in amino acid like glicyne ,alanine,beta alanine, aspartic acid etc. thus millers expiremnt gave an insight to the chances of abiogenenic synthesis of organic compounds in nature From a mixture of simple gases in which only source of carbon was methane. Protocell model or protocells The next question release the possible manner by which this organic compounds have organized then selfs to lead ultimately to the self duplicating molecules. Our knowledge in this direction is far inadequate. No experimental evidences to this step are available. However ,at present we assume that some chance association of protein, purines, pyramidines and other organic compounds might have given rise to a system that could reproduce. Once a system can produce itself from new materials of environment it is called to be alive. At the earlier time ,many combinations might have formed and degenerated many time. But some system sevived and from this substance originated life on earth. Where did life originate? We can interpret the past with the observation of the present.to quote Osborn. “the erliest forms of life were formed on the rocks of the ocean.” The body fluids of all animals have more or less same salt concentration as that of sea water.that is to say life was cradiled in the sea water and nature started her great experimentations with life about 4 billion years ago. “Organic life beneath the shore less waves Was born, and nurs’d in ocean’s pearly caves; First forms minute, unseen by spheric glass, Move on the mud, or pierce the watery mass; These, as successive generations bloom, New powers acquire, and larger limbs assume; Whence countless groups of vegetation spring, And breathing realms of fin, and feet and wing”. Protocell model As early as 1930 a protocell model became available in ‘coacervates’ droplet. Oparin held that large organic molecules synthesized abiotically on primitive earth formed large colloidal aggregates due to intermolecular attraction. The colloidal particles are called coacervates by oparin. The concentration of the polymer in a coacervate droplet is much grater some times hundred folds than that in  aqueous phase. This droplet represents open systems that passively concentrate materials from their environment. If an enzyme along with a monomer is added to the reaction mixture polymers are most formed and retained with in the droplet. Microsphere of fox Sydney fox from Florida university in 1957 made another protocell model called microsphere.he heated a mixture of 18 amino acids in anhydrous condition.160-200 degree Celsius and then cooled on cooling the amino acids had linked together and formed short chained molecules resembling oligopeptides. This molecules were termed ‘protenoids’ which had properties similar to those of natural proteins. When this protienoids dissolved in boiling water and then cooled, this formed tiny spheres which were suspended in the water. Fox termed them microspheres. This microspheres even though non living showed some properties of cell and where considered by fox as equalent to Oparins coacervates. Theories of organic evolution Different theories had been put forth to explain the cause and mechanism of organic evolution. Essentially all these theories agree in one important respects that variations constitute the essential raw materials of evolution. Various theories differ only in the explanation of the manner in which such variation occurs and operates in the production of new species. 1.	The theory of use and disuse or theory of inheritance of acquired character by lamarck 2.	The theory of natural selection by Charles Darwin 3.	The mutation theory by victor Hugo de vries 4.	The synthetic theory of evolution or modern synthetic theory of evolution by stebbins and co Theory of use and disuse by Lamarck Lamark was a noted French biologist and greatest of French evolutionist. He is known looked upon us “founder of complete modern theory of evolution. Lamarck publish his theory in 1809 in his famous treaties called philosophie zoologigue means philosophy of zoology.there are two cardinal principles in the Lamarckian theory they are The theory of use and disuse The theory of inheritance of acquired characters Theory of use and disuse The theory of use and disuse, put forward by Lamarck states that when an organ is put to constant use, it will develop more and more, while the theory of use and disuse explains that the constant disuse of an organ for a long time makes it under develop And ultimately leads to its degeneration. Inheritance of acquired characters According to Lamarck the structural changes acquired by an organism during its life time are preserved and are transmitted to the next generation. He called this “inheritance of acquired characters.” Germ plasm theory of agust weisman Theory of natural selection This theory was put forward by Charles Darwin. Darwin’s theory was not a speculative one but based upon careful and sustained study of various forms of animal and plant life over a period of 22 years.darwins theory waas based on three observation and two deductions from observations Tendency of organisms to in crease in geometrical ratio. But the number of organism of given species remain more or less constant. Variations occurs in individuals and specious in nature. Struggle for existence Natural selection Prodigality of production One of the impressive features of the living organism s is their capacity for excessive multiplication this tendency is known as prodigality of production. This is due to the biotic potential or reproductive potential of organisms. Biotic potentials are the inherent property of a population to reproduce or increase in number when all the environmental conditions are optimal. Struggle for existence Due to the excessive rate of multiplication on the part of various organism there is an everlasting competition or struggle between various individuals for food space and various other requirement and because of this the animals never increase in such number as in above. On the other hand, the populations of most species tend to remain more or less constant because of variants checks such as in adequacies in food supplies, living space , breeding space etc. This struggle may be intra specific or interspecific. Variation Means the tendency of offspring to differ from parents and also amongst themselves. Natural selection Darwin contented that in the struggle for existence those individuals endowed with slightly favorable variations, adapting them to meet the conditions of life more successfully would with stand the struggle for existence. While others will be gradually weeded out. That means nature select only adapted organism which become a different species by the accumulation of variation. According to Darwin therefore, it is nature which decides selection by an accumulation of small ,fluctuating, favorable variations through a number of generation under the force of natural selection new species have been evolved. Mutation theory Victor Hugo Diveries was a Dutch Botanist. He was the director of the botanical garden in Amsterdam and was the first to propose the mutation theory of evolution. The theory was based on the observation on Lamarck evening primrose growing wildly in a field near Armsterdam. Diveries maintained that evolution proceeds by large, discrete, and sudden changes and these changes were termed mutations. Now mutation is defined as sudden heritable change in the genotype of an organism. Now mutation is defined as sudden heritable change in the genotype of an organism. Synthetic theory of evolution The theory of evolution is based on a synthesis of the findings of genetics with other biological disciplines is called synthetic theory. Now a day when biologist referred to the theory of evolution, they think not on Darwin’s original statement of the theory but on modified an expanded version of Darwinism that took shades in 1930s and 1940s. The version was first known as neo Darwinism and later as synthetic theory of evolution. The neo Darwinism’s a modern synthesis between the Darwinian principle of natural selection and the findings of genetics. The modern synthetic theory of evolution recognizes five basic types of processes. That is Gene mutation Genetic recombination Changes in chromosomal structures and number Natural selection Reproductive isolation The first three are the forces for genetic variablities, with out which change cannot take place but they do not provide direction. Natural selection and reproductive isolation guide populations of organisms into adaptive channels. Besides, the working of these five basic processes is also influenced by three accessory processes. Migrations of individuals from one population to another. Hybridization between raises or closely related species. Both these increase the amount of genetic variability available for the population. The effect of chance acting on small population. (Genetic drift) may change the way in which natural selection guides the cause of evolution. It has been recognized that the three processes namely mutation, genet9ic recombination and natural selection are equally indispensable for evolutionary change to take place. They are so closely inter related that the question which of the three is the most important is irrelevant. Modern concept of evolutionary forces The modern or synthetic theory of evolution recognizes various forces for evolution. Nature only selects adapted individuals but if cannot produce any variations. Hence natural selection may be the chief factor in evolution built not the sole factor of force but any guiding factor. The synthetic theory recognizes the following forces for evolution. Mutation Random genetic drift Pre adaptation Reproductive isolation Natural selection In a randomly mating natural population and alternates equilibrium of alleles is produced. This is governed by a break down of isolating mechanisms, frequency in mutation, selection, random genetic drift etc. Mutation and genetic base of variation Random genetic drift Genetic drift is a change in the gene frequency in a population random drift is a random UN controlled fluctuation of gene frequency caused by a chance in mating patterns. This refers to the fact that variation in gene frequenci9es within populations can occur by chance rather than by natural selection. Random genetic drift or the Sewall Wright effect may be an important mechanism i9n evolutionary change in small or isolate populations. It is change in gene frequency in small breeding populations due to random fluctuations. In small populations not all the alleles which are representative of that species may be present chance3 even such premature accidental death near to maintain of an organisms. Which is the soul processer of a particular allele. would result in the elimination of that allele from the population ex: IF an allele has a frequency of 1% q= 0.01 in a population in 10 lahks then 10 thousand individual will poses that allele from that probability of loosing the allele from the small population by chance is much greater. Just as it is possible for an allele disappear from a population it is equally possible for it to drift to a higher frequency simply by chance. The ability of an animal to invade a new type of habitat and maintain itself ultimately depends on 2 factors. It must achieve a certain level of physical and physiological tolerance to gain a foot hole in the new locality It must have sufficient genetic variability to enable it to establish itself to face factors like climate and competition from other animal. The former is called pre adaptation and later post adaptation. Pre adaptation Animals especially to one mode of life have sometimes in evolution passed to another mode of life and become readapted ex: The fishes ancestral to amphibians passed from an aquatic to amphibian’s mode of life. Some times of fishes posses lungs and forelimbs. Hence it is possible for an animal to be adapted in someway long before it actually meets an environment to which it is best suited. This is called pre adaptation so when the environment changes or animal moves to a new environment characters or traits that where of no use formerly may prove to be highly advantages. Hardy Weinberg equilibrium Hardy Weinberg equilibrium is the mathematical erlation between gene frequency and genotype frequency with in populations. At equilibrium, frequency of classes can be approximated by binomial distribution and are as follows (p+q) 2 =p2 +2pq+ q2 In 1908 GH Hardy, a British mathematician and the German physician w. Weinberg independently develop a relatively simple mathematical concept now refers to as hardy Weinberg theorem, to describe the genetic equilibrium. In a sense its take that in the absence of migration, mutation and selection. gene frequencies and genotype frequencies remain constant generation after generation in a large, randomly mating population. Nature of evolution Speciation: it defined as a fundamental process in evolution were in one species in due course of time develops in to or more distinctive species. A species is a group of organism that interbreed themselves producing viable or fertile offspring. Sympatric and Allopatric Speciation Speciation in which two different species occupy the same area side by side but are separated by some isolating mechanisms is known as sympatric speciation. Ex: Rannapipiense, Ranna silvatica and Ranna catasbiana of the USA. All three frogs live in same area. Speciation were in geographic isolation place an important role is known as allopoatric speciation ex: Elephas indica, Elephas maximas. Isolation and isolating mechanisms Speciation is the process by which the new species are formed. Speciation is an irreversible process and when once a gene pool has reached at the species level it can never loose its identity while cross breeding with another species. In the evolutionary process once a new species is established, it maintains its integrity that is it no longer interbreeds with the parent species. It, may however perceive different evolutionary paths. Genetic divergent with in a single species is possible only when the members of a population of a single species are physically isolated from each other. So as to form small groups. Isolation is a major factor responsible for prevention of mating between members of different groups hence with out isolation. Prevention of inter breeding organic evolution is practically impossible. Isolating mechanisms An isolating mechanism may be defined as external or internal barrier which prevent interspecific inter breeding or reproduction or which might reduce the probability of gene exchange between two populations. These isolating mechanisms put a check on the interbreeding amongst related species and serve as an external barrier. Classification of isolating mechanisms Isolating mechanism generally fall under two major categories Spatial- isolation due to shear distance Genetic isolation Spatial isolation leads to the formation of Allopatric population while genetic isolation leads to Allopatric aswell as sympatric population. Isolating mechanisms in nature Geographic isolation Ecological isolation Seasonal isolation Sexual or ethological isolation Morphological isolation Physiological isolation Cytological isolation Hybrid in viability isolation Hybrid sterility isolation Geographical isolation in geographical isolation, the member of one population do not interbreed with the members of another because they inhabit different geographical localities.furter,the populations may be separated by vast stretches of land or water which form effective barriers preventing their interbreeding. Ex: Australian region, Galapagos Island. Ecological isolation or habitat isolation In this type of isolating mechanism the members of the same population may be separated from one another by their difference in their habitat. Seasonal isolation Here the different in breeding seasons prevent interbreeding ex: American toad’s buffo. Americanus and buffo fowleri. One is breeding much earlier in spring while other breeds rather very late in season. Sexual or ethological isolation In these types of isolation there is no morphological difference in sex organs but there are different in behavioral pattern that proceeds mating. The lack of mutual attraction has been traced to defense in pheromones, sexual recognition signs mating calls courtship etc. Ex:neworleans frogs, hyla vercicolor and hyla femoralis. Morphological or mechanical isolation This type of isolation is due to the difference that exists in the external genetalia of the different species. Physiological isolation It is also referring to us gamete incompatibility isolation here even though mating occurs gametes are prevented from effecting fertilization due to physiological factors. Cytological isolation Due to chromosomal incompatibility there will be a failure to initiate development Hybrid inviability or hybrid lethality isolation In this type of isolating mechanism embryo develop after fertilization. But it dies before reaching maturity Hybrid sterility isolation In this type of isolation hybrids are formed due to interspecific crosses but they are sterile. Mule is the classical example the cross of horse and donkey.