Synthetic Theory of Evolution for Competitive Exams

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Synthetic Theory of Evolution

Synthetic Theory Of Evolution - Migration And Change In Gene Frequency (Anthropology)

  • This theory of evolution is essentially a combination of Charles Darwin՚s concept of natural selection, Gregor Mendel՚s basic understanding of genetic inheritance, along with evolutionary theories developed since the early 20th century by field biologists, population geneticists and more recently by molecular biologists.
  • The Synthetic theory was fundamentally developed by three founders of theoretical population genetics namely R. A. Fisher in 1930, Sewall Wright in 1931 and J. B. S. Haldane in 1932.
  • The book, ‘The Genetical Theory of Natural Selection’ by Fisher is considered classic. The current understanding of the mechanism of evolution, though acknowledges the role of natural selection, differs considerably from the theory first outlined by Darwin
  • The population geneticists interpreted evolution in the terms of changes in gene frequency.

Migration and Change in Gene Frequency

  • Immigration When Local Population Is Large: Immigration to a local population when it is large in size does not produce a marked change in gene frequency of local population. In such a condition the migrant or straggler genes coming from another population has one of the two conditions- either the genes are swamped or eliminated or introduced in the population.
  • Immigration When Local Population Is Small: Immigration to a local population when it is small in size may or may not produce marked change in gene-frequency of the local population depending upon stability of the environment. For example, if the environment is stable- the population is perfectly adjusted to the local environment while in an unstable environment local population is unable to adjust hence, a hybrid gene is not formed.

Mutation and Change in Gene Frequency

Mutation and Change in Gene Frequency
  • Forward and Reverse Mutation: Mutations are the raw materials of evolution. They are changes in genes and are inherited in accordance with the Mendelian principles. The Dutch botanist, Hugo De Vries, first emphasized the importance of mutations in evolution. Indeed, he proposed a mutation theory of evolution intended not only to supplement but in large measure to support to Darwinian theory of natural selection.
  • Mutation is opposed by what is known as reverse mutation. This would also occur at a rather constant rate, although, judging by evidences available, at a lower rate. Thus, there are two opposed mutation rates.
  • 1. The rate at which wilder genes mutate
  • 2. the opposite rate
Mutation and Reverse Mutation

Genetic Drift

  • Also known as drift or Sewall wright effect or chance genetic drift is a phenomenon in which certain genes, without being advantageous to the population, either increase in frequency or may be fixed. This generally happens in small, isolated population. If population is large, it will be illogical to suppose disappearance of majority of persons.
Genetic Drift
  • If a population is not isolated some advantageous allele of the gene can be introduced in the population by migration which will hamper spread of disadvantageous allele.


  • Drift in Dunker Community, Pennsylvania: It has been found that gene-frequencies of many alleles has occurred due to bottlenecks and inbreeding.
  • Drift in Parma Highland, Italy: It has been reported that deviation in gene-frequencies for many traits including blood groups in this area.


  • Inbreeding usually refers to mating of two closely related partners. Brothers and sister mating and mattings among first cousin is very close inbreeding. Beginning with these extreme cases there is series of possible with outbreeding. The dividing line between inbreeding and outbreeding is thus not very hard and fast.
  • Inbreeding tends to eliminate hybrids from the population and to replace them by pure breeds of homozygous type. It does this by simple process segregation according to Mendel՚s first law of segregation. Thus, the proportion of homozygotes in the population is increased. Under such circumstances if a recessive gene is comparatively rare in the general population, inbreeding often allows two such genes to come together and express themselves. Autosomal recessive diseases are rare but are expressive in homozygous conditions.


Peppered Moth

Peppered Moth

  • Natural Selection moulds the genotypes of organisms so that they produce phenotypes best fitted to their environments. Consequently, the gene pool frequencies shift in the directions of their more adaptive alleles.
  • Since the environment is never stable for greater period of time, the nature of selection process also fluctuates. In a changed environment a trait may lose its adaptive value and may not be encouraged by selection, which may start favoring another trait that improves ‘fitness’ . It is probably that may be due to changing selection pressures. The example of peppered moth (Biston betularia) in connection with industrial melanism in moths provides insight into the operation of selection under natural condition.


Q1: Inbreeding tends to eliminate hybrids from the populations, this is done by simple law of ________

  1. Law of Segregation
  2. Law of Independent Assortment
  3. Law of Natural Selection
  4. Law of Dominance

Answer: (a)

Q2: The phenomenon in which certain genes without being advantageous to the population increases in frequency is:

  1. Gene Effect
  2. Position Effect
  3. Sewall Wright Effect
  4. Frequency Effect

Answer: (c)

Q3: The Theory of Mutation in evolution was propounded by

  1. Gregor Mendel
  2. Hugo De Vries
  3. R. A. Fisher
  4. Charles Darwin

Answer: (b)

Q4. The Synthetic Theory of Evolution was developed by:

  1. Gregor Mendel
  2. Fisher, Wright, Haldane
  3. Charles Darwin
  4. Henry Huxley

Answer: (b)

Q5: The book ‘The Genetical Theory of Natural Selection’ was written by:

  1. R. A. Fisher
  2. Sewall Wright
  3. Gregor Mendel
  4. J. B. S. Haldane

Answer: (a)

#Synthetic Theory of Evolution

#Migration and change in gene frequency

#Mutation and change in gene frequency

#Forward and Reverse mutation

#Genetic Drift



#Theories of Evolution

#Physical Anthropology


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