• progressive changes in organisms that persist over
• helps explain the great diversity, wide geographical
distribution, adaptations and origins of organisms
• 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
5. Modern Synthetic Theory
• It emerged around the middle of the 20th century from the
ideas of three authors specialized in different branches of the
1. T. Dobzhansky in genetics.
2. Ernst Mayr in the species of living beings.
3. George G. Simpson in the great categories of the
6. 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 Potential
3) Population genetics
5) Level of evolution
7. 1. Biotic Potential
• The innate capacity of a population to increase under
optimal conditions with suitable age & sex ratios
• Ideal conditions = biotic potential greatly increased
For example:: a Carp fish lays about 28 million eggs at a time
8. 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
9. 3. Population genetics
Evolution always take place in a population
A group of organisms of same species which
interbreed with one another in a particular
10. (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”.
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
11. • 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
4. All the genotypes in a population reproduce equally successfully.
12. (ii) Selection Pressure
• Mutations have harmful effect , on an individual & it eliminate them from
• 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
13. 3. Genetic Drift
• This concept was developed by Sewell Wright. . .
• It mainly concern with changes in gene frequencies
in small population.
14. 4. Speciation
According 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”.
15. 5. Level of Evolution
• Goldschmidt (1940) divide evolution into 2 types…
the subspecies of origin of smaller evolutionary differences.
16. (ii) Macroevolution:
The species & Genera or differentiation of a group of
animals by adaptive radiation. (change above the
It is also called Adaptive
17. 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
It accepts the random genetic change as a mechanism
of the important evolution, in addition to the
mechanism of the natural selection.
18. Some Generalized Trends in Evolution
Dollo`s Law : by Dollo according to him . . .
“evolution is usually irreversible process”.
19. Cope`s Law
• Proposed by E.D.Cope according to him. . .
“organisms have a tendency , towards increase in size
during their evolution”.