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- 1. TOPIC: MODERN CONCEPT OF EVOLUTION SUBMITTED BY- JYOTIRUPA DEVI EMAIL- jyotirupa500@gmail.com Roll no- 75e4610fed1711e998e11743374a34b0 COURSE NAME- Academic writing
- 2. ACKNOWLEDGEMENT This presentation is a part of assignment for week 13 for the course of Academic Writing.
- 3. INTRODUCTION • Evolution is the theory according to which complex forms are considered to have been derived from simpler ones. • Various theories have been proposed to understand when and the conditions of this evolution, such as- theory of eternity, theory of special creation, theory of abiogenesis, theory of organic evolution. • In 19th & 20th centuries, several theories have been put forward to know the causes, courses and effect of evolution and they were proposed by Lamarck, Darwin, De Vries, Weismann etc.
- 4. THEORIES ON EVOLUTION EVOLUTIONARY THEORIES MAINLY DEAL WITH : • HOW LIFE CHANGED AFTER ITS ORIGIN • THE VARIOUS PROCESSES THAT OCCURRED LEADING TO PRESENT LIFE FORMS • EVOLUTIONARY CHANGES AT ORGANISM AND POPULATION LEVEL • GENETIC CHANGES IN POPULATION OF ORGANISMS THROUGH TIME THAT LEAD TO DIFFERENCES AMONG THEM • PREDICTIONS REGARDING POSSIBLE EVOLUTIONARY CHANGES IN NEAR FUTURE
- 5. LAMARCKISM Jean Baptist de Lamarck published the first truly mechanistic theory of evolution in his book philosophie zoologique . ECOLOGICAL CONDITIONS IN WHICH ORGANISM LIVES CAUSE IT TO HAVE CERTAIN “ NEEDS ” THESE NEEDS ARE MET BY : MODIFICATION OF OLD ORGANS PRODUCTION OF NEW RUDIMENTARY ORGANS BY CONTINUOUS USE OF ORGANS, THEY INCREASE IN SIZE AND FUNCTIONAL CAPACITY BY DISUSE, THEY MAYBE DEGENERATED AND BECOME LOST DURING EVOLUTION CHARACTER CHANGES BROUGHT OUT BY ENVIRONMENT DURING THE LIFE OF AN INDIVIDUAL BECOME HEREDITARY AND THUS CAN BE TRANSMITTED TO THE NEXT GENERATION
- 6. EXAMPLE OF LAMARCKISMEXAMPLE OF LAMARCKISM
- 7. DARWINISM • Charles Robert Darwin, an english naturalist proposed and provided evidence for the scientific theory that all species have evolved over time from one or a few common ancestors through the process of NATURAL SELECTION. • He coined the term NATURAL SELECTION to describe the process by which organisms with favorable variations survive and reproduce at a higher rate. • DARWIN’S THEORY CAN BE SUMMARIZED AS : • EVOLUTION AS SUCH : World is steadily changing and organisms transform over time • COMMON DESCENT : Each and every group of organisms descended from a common ancestor. There is a single origin of life on the earth • GRADUALISM : According to Darwin’s theory, evolutionary change takes place through gradual change of populations and not by sudden production of new individuals that represent a new type. • NATURAL SELECTION : Evolutionary change comes about through abundant production of genetic variation in every generation. The few individuals who survive have a particularly well adapted combination of inheritable characters.
- 8. EXAMPLE OF EVOLUTION BY NATURAL SELECTION
- 9. MUTATION THEORY OF EVOLUTION • Proposed By Hugo De Vries , A Dutch Botanist • HE WORKED ON EVENING PRIM ROSE (Oenothera Lamarckiana) • He Allowed Self Pollination For A Number Of Generations • Majority Of Plants Of Generation 1 Were Of Parental Type Only • THESE SPECIES WERE TERMED AS ELEMENTARY SPECIES (Produced In Large Nos.) • 837 Out Of 54,343 Members Were Found To Be Very Diff. for different Characters. • On Observing Consecutive Generations, He Obtained A Much Longer New Type Called O.Gigas . • HE ALSO FOUND NUMERICAL CHROMOSOMAL CHANGES IN THE VARIANTS • Conclusions Drawn By De Vries : • Evolution Is A Non Continuous Process And Occurs By Mutations • Elementary Species Are Produced In Large Nos. To Increase Natural Selection • MUTATIONS ARE RECURRING (I.E Mutants Appear Again And Again). This Increases Chances Of Their Selection By Nature • Mutations Occur In All Directions So May Cause Gain Or Loss Of Any Character. • Evolution Is A Discontinuous And Jerky Process And Not A Gradual Process As Told By Darwin And Lamarck.
- 10. Weismann’s theory • It states the continuity of the germplasm and non- transmission of acquired characters • According to him, variations are of two types- • 1. congenital- organisms are borne with them • 2. acquired- acquired during the life time • Organisms are made up of two substances 1.germplasm- produces reproductive cells 2.somatoplasm- it produces only body cells • Continuiting of germplasm is maintained from generation to generation
- 11. • Any change in somatoplasm cannot get transmitted as it is discontinous • Only variations in the germplasm can be inherited • Some determiners are thought to be present which influences heredity CRITISISM: • This theory were highly appreciated by later workers • Doesnot hold true with all organisms • Difficult to explain certain cases like asexual reproduction or regeneration
- 12. MODERN THEORY OF EVOLUTION• Modified form of Darwinism and mutation theory of de vries. • According to Stebbins, the modern theory of evolution recognizes 5 basic types of processes- a) Gene mutation b) Changes in chromosome structure c)Genetic recombination d) Natural selection e)Reproductive isolation • Hybridization and migration are also another factors. • First three provide the genetic variability and later two provide direction to the evolutionary process. • All these processes are interrelated with each other
- 13. • Stebbins explained the synthetic theory in a popular way. • He compared it with the movement mechanism of a vehicle: i) Population = vehicle ii) Gene mutation = fuel of automobile iii) Genetic recombination = engine iv) Natural selection = driver v) Structural changes in chromosome = accelerator vi) Reproductive isolation = directive signs
- 14. MAIN FEATURES OF MODERN THEORY OF EVOLUTION •Population having a distinctive type of variable character is given the rank of sub-species and finally converted into species through natural selection •Within each sub-species a particular gene combination is present where natural selection operates •Random mutation takes place within each sub- species •Mutated sub-species are isolated from each other •Gene exchange is restricted due to isolation among entire population thus leading towards new species formation
- 15. FACTORS OF MODERN THEORY1. GENETIC VARIATION IN POPULATION-Evolution-the change in gene pool, occurs through accumulation of genetic variations over long period of time such changes in gene pool is known as change in gene frequency. Factors for gene variation – Migration Non-random mating Genetic drift Mutation Gene recombination a) MIGRATION- Movement of organisms from one location to another •Breeding of immigrants with the host population adds new alleles to the gene pool of the host population, • it can provide a sudden influx of alleles after matting is established it alter the existing proportion of alleles in the population b) NON-RANDOM MATING- It occurs because sometime one organism chooses to mate with another based on certain traits • which changes the genetic combination that appear in successive generation • It can occur in two forms: Inbreeding and Outbreeding inbreeding lead to a reduction in genetic variation ,out breeding can lead to an increase
- 16. c) GENETIC DRIFT- It refers to the chance for elimination of the genes of certain traits • when a section of population migrates or die of natural calamities it alter the gene frequency of the remaining population • it eliminates certain alleles and fixases the other alleles there by reducing the genetic variability of the population. FOUNDER EFFECT- • When a small group of people called founders, leave their homes, the population in a new settlement have different genotype frequencies population formation of a different genotype in a new settlement is called the founder effect.
- 17. BOTTLENECK EFFECT- Natural calamity, like earthquake, fire or flood, may greatly reduce the size of a population • This situation with reduced genetic variability is called bottleneck • Among the survivors certain alleles may be over represented, some may be under represented and some alleles may be totally eliminated.
- 18. d) MUTATION • Mutation are the major source for evolution. • Mutation alters the base sequence in a gene or gene sequence in a chromosome. • Due to gene mutation and chromosomal mutation, two type of changes found. • Gene mutation have the effect of increasing the gene pool by adding to the number of alleles available at a locus. • Most of the mutation are deleterious mutation could have a direct influenced on that rate and direction of evolution only if they occurred on an essentially uniform, genetic background . • Mutation limits the rate of evolution which expressed in terms of nucleotide substitutions in a lineage per generation. • All the potentially useful mutation would have occurred at least once during the evolutionary history of the species and incorporated by natural selection.
- 19. e) GENE MUTATION- A random change in the base sequence of a gene affects the allele’s frequency in the population • It is mainly of point mutation ,occurs by substitution ,addition or deletion of one or more bases . • mutations are essential to evolution every genetic feature in organisms was initially the result of a mutation and the new genetic variant spreads via reproduction. • even deleterious mutations can cause evolutionary changes, especially in small population by removing individuals that might be carrying adaptive alleles at other genes. f)STRUCTURAL CHANGE OF CHROMOSOME- It changes the morphology and number of chromosomes at times and such a variation may manifest in the phenotype. • deletion, inversion, translocation, duplication of a segment of a chromosome couses morphological changes • numerical changes take place by aneuploidy and polyploidy • the chromosomal aberrations result in loss of genes, new positions for gene or addition of genes, gene variation results in change in gene frequency.
- 20. g) GENE RECOMBINATION- Phenotypic variability of a population depend upon three factor- Enviromental condition, mutation and recombination. • is an event occurring by the crossing over of chromosomes . • for the establishment of new variation by natural selection a new adaptive combination is form out of a gene pool through the combined action of mutation and gene recombination
- 21. h) HYBRIDIZATION: • A controversial topic in case of evolutionary study. • Though being a rare event in nature,it has huge consequences. • If hybrid are less fit, results in population limitation & prezygotic isolation. • If hybrid are more fitter than parents, it leads towards new speciation.
- 22. 2. REPRODUCTIVE ISOLATION: • Collection of evolutionary mechanism, behaviors and physiological processes. • Ensures that interspecific offspring are sterile. • Reduction of gene flow between related species. • longer the groups isolated, more different they are. • Also Change in environment influences isolation process. • Example: Living organisms are most diverse not due to different habitats but due to their different ways of adaptation to the same habitat.
- 23. Heredity The transmission of variation from parents to offspring is called heredity which is an important mechanism of evolution. Organisms possessing heredity characteristics are favored in struggle for existence. Thus, the offspring are benefitted from advantageous characters of their parents.
- 24. Speciation • The population of a species present in different environment and separated by geographical and physiological barriers by different genetic due to mutation, recombination, hybridization, migration etc. • Thus, these population becomes different from each other morphologically and genetically isolated, forming new species.
- 25. 3.NATURAL SELECTION • Earlier selection was regarded as a negative force, eliminating the new unfit variants. • In modern concept, selection is said to be a creative force. • This belief comes from following four trends- i. Formation of sub-species involves mutation with a small effect but in a high frequency. ii. Normal heterozygous condition might be led towards pure line through selection. iii. Natural selection is the guiding force and accumulates the changes. iv. effectiveness of selection is also influenced by complexity of environment.
- 26. CONCLUSION • Based on data from all biological science • Is the result of the work of no. of scientists namely T.Dobzhansky, R.A.Fisher, J.B.S.Hold and S.Wright, Ernst Mary and G.L. Stabbins • maintains the mutation and sexual recombination selection fashions these materials genotypes are protected by isolation
- 27. • Thus in the conclusion we can say that the modern theory is the theory is the result of the work of number of scientist viz T.Dobzhansky, R.A. Fisher, J.B.S. Hold and S.Wright, Ernst Mary and Stebbins.
- 28. REFERENCE • Mitra J.N. , Mitra D , Chowdhjury S.K. : Studies in Botany, volume two • Stebbins G. Ledyard, Jr. : Variation and evolution in plants • Stebbins G. Ledyard : Process of Organic Evolution • Trivedi M.C. : Evolutionary Biology • Verma P.S., Agarwal V.K.: Concept of Evolution • Singh Harjendra, Chaturvedi C.M. : Organic Evolution • A text book of biology ,P.S. DHAMI, Dr. G CHOPRA, Dr. H. N. SRIVASTAVA