INTRODUCTION:-”EVOLUTION” Lamarck-ism;-Lamarck-ism is based on the following 4 postulates?

INTRODUCTION:-”EVOLUTION” means change,change in form and behaviour of organisms between generations.The forms of organism at all levels from DNA sequences to macroscopic morphology and social behaviour,can be modified from those of their ancestors during evolution.HOWEVER, not all kinds of  biological changes are included in the defination.THEORIES OF EVOLUTION:-There are 4 main theories of evolution named as;? LAMARKISM or theory of inheritance of acquired characters? DARWANISM or theory of natural selection? MUTATION theory of De Vries? NEO DARWANISM or modern concept or synthetic theory of evolution1) LAMARKISM;-It is also called “Theory of inheritance of acquired characters” and was proposed by a great French naturalist, Jean Baptiste de Lamarck (Fig. 7.34) in 1809 A.D. This theory is based on the comparison between the contemporary species of his time to fossil records. Lamarck was incharge of invertebrate collection of at the Natural history museum in Paris.He presented a mechanism to explain how specific adaptations evolve.His theory is based on inheritance of acquired characters that how the changes that are attained in the body of an organism due to changes in environment are passed to their next generation.Postulates of Lamarck-ism;-Lamarck-ism is based on the following 4 postulates? New needs:organisms live in some kind of environment.They had to face the factors like temperature,light,food,air,light.They put on some kinds of adaptations to survive and to handle such a situation.To fulfill their new need they have to do some extra effort like change in habitat or environment.? The use and disuse of organs:new habitats that are acquired by organisms demands a greater effort and more use of some organs greater to meet the needs of the environment and disuse of some organs which are of no use in such a condition makes them to deteriorate.? Inheritance of acquired characters:Lamarck proposed that the acquired characters are inheritable and are passed to off springs so that when they are born they already have the characters to face the existing environment.? Speciation:according to Lamarck acquired characters passed generation after generation and hence every newborn may have all the acquired characters and hence lead to the formulation of a new specie after successive generations.So,individual is a sum of all the acquired characters generation after generation.Summary of the four postulates of Lamarck:a. The components of living organisms tend to increase in size.b. Need results in the production of new organs.c. Continuous use of the organs makes them more developed and disuse of an organ makes the organ to deteriorate.d. Acquired characters are inheritable and accumulate generation after generation to form a new specie.Evidences of Lamarckism;? GIRAFFE;developed from ancient deer like ancestors.they have long neck and long forelimbs due to stretching its neck for the sake of food.These body parts were elongated so as to eat leaves on the long branches and trees due to deficiency of food in Africa.This is an example of extra use of an organ ? SNAKE;the development of todays limbless snake from limbed ancestors is an example of disuse of organs and their deterioration.? ACQUATIC BIRDS;the development of aquatic birds like ducks and geese from terrestrial ancestors due to continuous disuse of wings and development of webs between their toes for wading purposes is an example of extra use and disuse of organs.? FLIGHTLESS BIRDS;ostrich is a flightless bird developed from a flying ancestor.Due to living in an environment having plenty of food and protection resulted in the deterioration of wings.Hence they are flightless birds.Significance:1) It was a first comprehensive theory of biological evolution.2) This theory exerts a great stress on the acquired characters as primary product of evolution.Darwinism (Theory of Natural Selection):A. Introduction:Charles Darwin (Fig. 1) (1809-1882 A.D.), an English naturalist, was the most dominant figure among the biologists of the 19th century. He made a broad investigation of nature for more than 20 years, particularly when he joined the endeavor on Beagle to South America. (Fig. 2) and investigated South America, the Galapagos Island and different islands. He gathered the perceptions on creature circulation and the connection amongst living and terminated creatures. He found that current living structures share similarities from numerous points of view, among themselves as well as with the life shapes that existed a great many years prior, some of which have turned out to be wiped out.  He expressed that each populace has worked in varieties in their characters. He found that all living organisms, including humans are modified descendants of previously existing life forms. Darwin perceived the origin of species and adaptations as closely related processes. In 1884, Darwin wrote a long essay on the origin of species and natural selection, but before it could be published, Alfred Wallace, a young naturalist, working in East Indies developed a theory of natural selection, identical to Darwin’s. Wallace’s paper, along with extracts from Darwin’s unpublished 1884 essay, was presented to the Linnaean society of London on July 1, 1858.                    Darwin expounded his hypothesis of development in a book entitled “On the Origin of Species by methods for Natural Selection”, distributed on 24th Nov, 1859.In his book, Darwin developed the two main points:• Descent with Modification.     • Natural SelectionIn this theory, Charles Darwin proposed the concept of natural selection as the mechanism of evolution.B. Proposes of Darwinism: Fundamental proposes of Darwinism are: ? Geometric increment. ? Limited food and space.? Struggle for existence.? Variations.? Survival of the fittest.? Legacy of valuable varieties.? Speciation.? Geometric Increment:As indicated by Darwinism, the populaces tend to increase geometrically and the conceptive forces of living life forms (biotic potential) are significantly more than required to keep up their number e.g., Paramecium partitions thrice by twofold splitting in only 24 hours under good conditions. Because of current circumstances, a Paramecium can create a clone of around 280 million Paramecia in only one month and in five years, can deliver Paramecia having mass equivalent to 10,000 times than the span of the earth. Other quickly duplicating life forms are: Oyster (114 million eggs in one generating); Ascaris (70, 00,000 eggs in 24 hours); housefly (120 eggs in a single laying and laying eggs six times in a late spring season). Essentially, the plants likewise replicate quickly e.g., a solitary night primrose plant creates around 1, 18,000 seeds and single plant delivers a couple of million spores. rvive and repIndeed, even moderate rearing living beings replicate at a rate which is significantly higher than required e.g., an elephant turns out to be sexually develop at 30 years old and amid its life expectancy of 90 years, creates just six offsprings. Along these same lines, if all elephants survive then a solitary combine of elephants can deliver around 19 million elephants in 750 years.These examples confirm that every species can increase tremendously within a few generations and occupy all the available space on the earth, if all organisms survive and repeat the process.? Limited food and space:According to Darwinism,a population tends to increase geometrically, but the food increases only arithmetically. Therefore,the two main limiting factors on the tremendous increase of a population are: limited food and space, which together constitute the major part of carrying capacity of environment. These do not allow a population to grow infinitely which are nearly stable in size except for seasonal ups and downs.? Struggle for existence:Due to tremendous increase in populations but limited food and space, there starts an everlasting competition and war between individuals having similarities in their features. Therefore, every living organism desires to have an upper hand over others.The competition between living organisms for the necessities of life like food, space, etc. for their survival is called struggle for existence, which further is of three types:(a) Intraspecific:Between the members of same species e.g. two dogs struggling for a piece of meat.(b) Interspecific:Between the members of different or various species e.g. between predator and prey.(c) Environmental or Extra specific:Between living organisms and unfavourable environmental factors like heat, cold, flood, earthquakes etc.Intra specific is the strongest factor among the other three  factors ,as the struggle is between the members of the same species.In this struggle, the majority of individuals die before reaching the sexual maturity and only few  survive that reaches the reproductive stage. So, the struggle for existence acts as check and balance on the tremendous increase in the population of each species.? Variations:Variation is the law of nature. According to this law of nature, no two individuals except identical (monozygotic) twins are same/identical. This everlasting competition has compelled them to adapt according to the conditions to utilize the natural resources,so they can survive successfully.Darwin proposed that the variations are generally of two types—continuous variations and discontinuous variations. On the basis of their effect on the survival chances , the variations may be neutral, harmful and useful.Darwin proposed that living organisms adapt themselves  to the changing environment due to useful continuous variations.? Natural selection or Survival of the fittest:In Natural Selection, nature selects only those individuals out of the total population which are with useful continuous variations and are best adapted to the environment than the less fit individuals.Natural Selection can amplify or diminish only those variations that are heritable.It is noteworthy to say that adaptations that an organism acquires by its own actions are not heritable.The specifics of natural selection are regional and timely; environment factors vary from place to place and from time to time.An example of natural selection in action is the evolution of antibiotic resistance in bacteria.? Inheritance of usefull variations:Darwin believed that the selected individuals with the best features  pass their useful continuous variations to their offsprings so that they are born fit to the fluctuated environment.? Speciation:Darwin suggested that the differential skills and ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations thus leading to the evolution of a new species.C. Evidences in favour of Darwinism:1. There is a close correspondence between natural selection and artificial selection.2. The remarkable cases of resemblance can be achieved only by gradual changes occurring simultaneously both in the model and the mimic.3. Mutuality  between position of nectaris  in the flowers and length of the olfactory organ of the pollinating insect.D. Evidences against Darwinism:Darwinism is not able to explain:1. Small variations in those organs that are useful only when fully formed e.g. wing of a bird. Such organs will be of no use in incipient stage.2. Inheritance and function of vestigial organs.3. Inheritance of organs like antlers in deer and tusks in elephants.4. Unable to differentiate between somatic and germinal variations.5. Causes of the variations and the mode of transmission of variations.6. It was also rejected by Mendel’s laws of inheritance which state that inheritance is particulate.So this theory explains only the survival of the fittest but does not explain the arrival of the fittest so Darwin himself admitted that natural selection has been main but not the exclusive means of modification.Principle of Natural Selection:It was proposed by Ernst Mayer in 1982. It resulted from five observations and three inferences as shown in the following table. This principle manifests that natural selection is the differential success in reproduction and enables the organisms to adapt themselves to their environment by development and formation of small and useful features/characteristics.                     Observations                        Inferences1. All species have a great potential of fertility that population would increase at an alarming rate if all individuals were born and reproduced successfully.2. Almost all populations are stable except some seasonal fluctuations.3. Natural sources are limited.4. Individuals vary in their characteristics.5. Much of this variation is heritable. i. Increment in more individuals than environment lead to the struggle for existence, resulting in the survival of the fraction of offsprings each generations.ii. Those individuals whose inherited characters fit them best in the environment are likely to leave more offsprings than less fit individuals.iii. This lead to the gradual change in the population with favourable characteristics over generations.  Hence, these favourable variations pass over generation after generation and lead to speciation. So natural selection works through interactions between the environment and inherent variability in the population.2) MUTATION THEORY OF EVOLUTION:-The mutation theory of evolution was proposed by a Dutch botanist, Hugo de Vries (1848-1935 A.D.)  in 1901 A.D. in his book named as “Species and Varieties, Their Origin by Mutation”. He worked on evening primrose (Oenothera lamarckiana). Experiment: Hugo cultured some O.lamarckiana in his botanical garden.He allowed the plants to self fertilize and hence he obtained the next generation.Again he allowed the plants to self pollinate and thus he obtained the next generation.he repeatedly obtained many generations in this way.                                                                                                                     ? Observation: He observed that most of the plants of first generation were parental like and showed very less variation.But very few members were found to be differ in size shape, seed colour, bud shape and all other properties.These markedly different plants were known as primary or elementary species.He also found the numerical chromosomal change in the variants.? Conclusion:  1.He concluded that evolution is a discontinuous process and it occurs by mutation.Individuals with mutation are known as mutants.2.Elementary species are produced in a great number to increase the chances of selection by nature.3.The mutants appear again and again and increases the chances of selection by nature.4.Mutations occur randomly so may cause the gain or loss of character.5.Mutation is some what different from small fluctuation.? Evidences in favour of mutation theory:1.)Appearance of short legged sheep from long legged parents in a single generation in 1791 A.D (fig.7.39) is an evidence of mutation theory.It was first observed by an American farmer. 2.)Appearance of polled Hereford cattle from horned parents in a single generation is also an important evidence.4)NEO-DARWANISM:- Neo Darwinism is the interpretation of Darwinian evolution through natural selection as it has been variously modified since it was first proposed.It is an interpretation of Charles Darwin theory of evolution by natural selection and George Mendel theory of genetics as the basis of biological inheritance. Postulates of Neo-Darwinism:1-Genetic variability;sources include mutation and chromosomal aberrations.chromosomal aberration include deletion,insertion,trans location and duplication.2-Numerical chromosomal mutation;include change in number of chromosome3-Gene mutation;it include point mutation,recombination of genes,hybridization,genetic drift.4-Natural selection; differ from the Darwinism in the respect that it does not related to the survival of the fittest rather it operates through differential reproduction and comparative reproductive success.TYPES OF EVOLUTION ON THE BASIS OF SCALE.There are two main types of evolution.1.Microevolution2.MacroevolutionMICROEVOLUTION:”The evolution which takes place at small scale that is which occur to a few genes and happens to populations in short period of times.”MACROEVOLUTION:”The evolution which takes place at large scales or the changes that take place over large time periods”For Example: Formation of new groups and species.EVIDENCES OF EVOLUTION OF LIFE.On the basis of types of evolution, there are following evidences of evolution of life on Earth:? MORPHOLOGICAL EVIDENCES.? EMBRYOLOGICAL EVIDENCES.? PALAEONTOLOGICAL EVIDENCES.? MOLECULAR EVIDENCES.? BIOGEOGRAPHICAL EVIDENCES.? DIRECT OBSERVATIONS.MORPHOLOGICAL EVIDENCES:Although there exist great differences between the organisms of different groups and species, but there are certain similarities as well. These Morphological evidences are derived from following:? HOMOLOGOUS AND ANALOGOUS ORGANS.? VESTIGIAL ORGANS.? CONNECTING LINKS.1. HOMOLOGOUS AND ANALOGOUS ORGANS:HOMOLOGOUS ORGANS: “These are the organs which have similarity in their structures and origins, look different and have different function.”The evolution on this basis is called as divergent evolution. This is because of  the different functions of same structure.For Example; If we look at the forelimbs of dogs, humans, bats and whales they look different and have different functions. But when we observe their bones structure, the pattern of bones is same in each species. Which shows that they have common ancestors.  Which shows that evolution take places which make them functionally different from one another. ANALOGOUS ORGANS: “These are the organs which are functionaly same but structurally different “The evolution on this basis is called convergent evolution. This is bescause in this form functions are same.For Example: The functions of wings of insect or bird or bat or pterodactyl is same that is, flying. But Insects wings have no structure similarity with that of vertebrates .It shows that evolution take places which causes the change in their structures. VESTIGIAL ORGAN:  ” The reduced,degenarate ,non_functional organs which may have some function in past but now is no more function is called vestigial organ”EXPLANATION: In 1971 the Encyclopedia Britannica claimed there were more than 100 vestigial organs in man, and even as recently as 1981, some biology textbook authors were claiming as many as 100 vestigial organs in the human body.1 One of the most popular current biology textbooks declares that “many species of animals have vestigial organs.” Examples cited in humans include the appendix, “tailbone,” and muscles that move the ear. A website given  by the Discovery Channel, for example, assures us that “the human body has something akin to its own junk drawer,” and that this junk drawer “is full of vestigial organs, or souvenirs of our evolutionary past.”3 REFERENCES:1) S.R. Scadding, “Do Vestigial Organs Provide Evidence for Evolution?” Evolutionary Theory 5 (1981): 173–176. 2)  K.R. Miller and J. Levine, Biology: Teachers Edition (Upper Saddle River, NJ: Pearson Prentice Hall, 2006), p. 384. 3) EXAMPLES.  The tail bones in humans, appendix in humans, pelvic bones in whales and snake etC CONNECTING LINKS: “The organisms which possess the properties of other organisms of other group or species is called connecting links”Example:  Archaeopteryx   show collecting link between reptiles and birds. This bird has beak with teeth(reptiles) and wings on body like (birds). This collecting link provide us the fact that one group is evolved from some other group and both may have same ancestor.EMBRYOLOGICAL EVIDENCES:”Embryology is basically the study of stages of development of an embryo”The evidence of evolution is as follow:• All the organisms at their embryo state passes through same stages like Blastula, Gastrula.• The embryo of all vertebra has similar structure at their early stages of development.• All embryo of vertebra forms single celled zygote. EXAMPLE: All embryos like of human, fish, chicks they have gill pouches at their early developmental stage.  As development proceeds these structure take characteristics function of particular species. For examples gill pouches in human develop into lungs.FIGURE 1HUMAN EMBRYO•  FIGURE 2 CHICK EMBRYO•  • All above mentioned features strongly support that all vertebrates have same common ancestor.PALEONTOLOGICAL EVIDENCES:Paleontology the study of the fossil fuels of organisms and plants. Fossils are the remains of plants and animals of the past found embedded in the earth curst.? The first fossil fuels are found in rock that build up in layers known as strata.The earliest fossil fuels of geographical era is that of bacteria. After this, that of invertebrates then proceeds as fishes, amphibians, reptiles, birds and at the last is of human beings.EXAMPLE: The fossils fuels of horses, human, elephants , camels  shows that they have common ancestor. Their number of toes have decreased for speed and their sizes also varied.  Many fossil fuels evidences have been lost or broken from the past. This is because some soft bodies organisms have lost their fossils or even some have not fossil fuels.? The fossils fuels evidences are made possible by calculating the ages of fossil fuels of different organisms of different geographical regions. The main method of calculating the ages of fossil fuels are:? CARBON DAITING: Radiocarbon dating is a method that provides objective age estimates for carbon-based materials that originated from living organisms. 1REFERENCE:1. American Chemical Society National Historic Chemical Landmarks. Discovery of Radiocarbon Dating (accessed October 31, 2017)MOLECULAR EVIDENCES:All organisms have some common things at molecular level such as:• All organisms are made of simple unit of life is called cell. Either a organisms contain single or multiple cells ,it depends on its complexity.• All organisms have same genetic material that is DNA.• All have same basic steps of processes of Translation and Transcription• All have same molecular buildings of Amino Acids.• All have cellular organelle as RIBOSOMES.All have energy storing and providing ATPAll these features show that all organisms have some common ancestors. They show the similar processes because their ancestors have same processes. They have same genetic material as that of their ancestors.Organisms which shows same chemical properties have same evolutionary relations. FOR EXAMPLE ;All human blood proteins are same to that of proteins of Chimpanzee ,  only plants and some algae have chlorophyll molecule for photosynthesis.BIOGEOGRAPHICAL EVIDENCES:It is the study of distribution of life forms over various geographical regions during various time periods.Biogeography is a strong evidence of evolution of life. It is first suggested to Charles Darwin. According to him species arises from common ancestor. He observed the animals of Galapagos island and noticed that thy were similar to that of South American mainland but dissimilar to other island under same conditions. After this he declared that these are migrated from South American island. As populations passes ,changes occur and gradually these changes lead to formation of New Species.DIRECT OBSERVATION:Direct evolution can be made at microevolution. These observations take place at bacteria and microbes. Mainly it takes place at drug resistance bacteria and pesticides resistance bacteria. In past, bacteria are not resistance but now due to the fact that various bacteria are able to resist the drugs. Now bacteria are mostly drug resistance.