Theory of evolution in this slides i have mentioned all the theories of evolution including modern concept of evolution.

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