Modern Synthetic Theory of Organic Evolution

Presenting To Sir.Shahroz Khan Presenting By Abdul Qahar

& Asar Khan

EVOLOTION•progressive changes in organisms that

persist over time •helps explain the great diversity, wide

geographical distribution, adaptations and origins of organisms

Neo-Darwinism•Theory of evolution and human origin derived

from Darwinism which, supported by scientific advances in cytology, biochemistry, genetics, etc.

•They observed the influence of the environment on the evolution of the species, and the heredity of acquired characters

Modern Synthetic Theory • It emerged around the middle of the 20th century

from the ideas of three authors specialized in different branches of the evolution:

1. T. Dobzhansky in genetics.2. Ernst Mayr in the species of living beings. 3. George G. Simpson in the great categories of the

organisms.

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Modern Synthetic Theory of Evolution•R.A.Fisher & S.Wright provide much needed

statistical basis to this theory. This theory can be stated as follows:

1) Biotic Potential2) Variations3) Population genetics4) Speciation5) Level of evolution

1. Biotic Potential•The innate capacity of a population to

increase under optimal conditions with suitable age & sex ratios present.

•Ideal conditions = biotic potential greatly increased

For example:: a Carp fish lays about 28 million eggs at a time

2. Variations• Darwin recognized 2 kinds of variations

• 1. Non-Hereditary: -> appears during the life of an animal & are not

passed on to the offspring's.

• 2. Hereditary: -> these are important for evolution because it can

passed on to the offspring`s.

• Genetically controlled variations are produced by

(a) Mutations (b) Chromosomal change (c) Recombination

3. Population geneticsEvolution always take place in a population•Population: A group of organisms of same species which

interbreed with one another in a particular geographical are.

(i) Genetic Equilibrium• G.H.Hardy (Mathematician) and W.Weinberg a German physicist in

1908 stated in his Law that. . .

• “ in a large randomly mating population, without selection and mutation the gene frequency remains constant”.

• Mathematically::

p + q = 100% (p= frequency of one allele in population (T) ). (q= frequency of second allele (t) ).Substituting F1 generation in terms of p & q the phenotypic equation will

be P2 + 2pq + q2 = 100% or 1 (TT) (2Tt) (tt)

If frequencies of “p” and “q” are equal than . . . (.5 x .5) + 2 (.5 x .5) + (.5 x .5) = 1 (.25) + (.50 ) + (.25) = 1 1 = 1

• If the frequencies of “p” is 60% and “q” is 40% than , (.6 x .6) + 2 (.6 x .4) + (.4 x .4) = 1 (.36) + (.48) + (.16) = 1 1 = 1• Silent features of Hardy Weinberg Law are . . .

1. The gene & genotype frequencies of each allele in a population remain at an equilibrium generation after generation.

2. The mating is completely random phenomenon in a population.

3. The equilibrium in gene & genotype frequencies occurs in a large populations.

4. All the genotypes in a population reproduce equally successfully.

(ii) Selection Pressure• Mutations have harmful effect , on an individual & it eliminate

them from the population. • e.g Peppered Moths (Biston betularia) by Fischer He observed

that only white colored moths are present in England until 1845. in 1845 a single black color moth appear in industrial center & up to 1895 its population increase 99%.

3. Genetic Drift•This concept was developed by Sewell Wright.

. . • It mainly concern with changes in gene

frequencies in small population.

4. SpeciationAccording to Ernst Mayer . . .“A species is an actually or potentially interbreeding

population that does not interbreed with other such populations when there is opportunity to do so”.

5. Level of Evolution•Goldschmidt (1940) divide evolution into 2

types…(i) Microevolution: the subspecies of origin of smaller evolutionary

differences.

(ii) Macroevolution: The species & Genera or differentiation of a

group of animals by adaptive radiation. (change above the species level).

It is also called Adaptive Radiation…

Modern Synthetic Theory vs Darwin Theory

• We can summarize the important differences of the Modern Synthetic Theory of evolution with the Theory of Darwin in the following:

It accepts the random genetic change as a mechanism of the important evolution, in addition to the mechanism of the natural selection.

Some Generalized Trends in Evolution

Dollo`s Law : by Dollo according to him . . . “evolution is usually irreversible process”.

Cope`s Law

•Proposed by E.D.Cope according to him. . .“organisms have a tendency , towards increase

in size during their evolution”.

Still Confused ? Let`s seewhat's next?

• Be attentive

Presenting By: A Q and A k (M.Sc Zoology) AWKUM Buner Campus