Evolution & Its Principles for Competitive Exams

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Image of Evolution and Its Principles

Evolution & Its Principles: Speciation & Detail About Species (Physical Anthropology)

  • Physical Anthropology is the branch of anthropology that deals with human evolutionary biology, physical variation and classification. In this session we will study about the evolutionary aspect of human beings. Human evolution is the evolution of Homo sapiens from their ancestors whereas human variation refers to differences that exist among individual population.

Human evolutionary biology

Human Evolutionary Biology

Image of Herbret Spencer

Image of Herbret Spencer

Herbret Spencer

  • Herbert Spencer, an English philosopher, first used the term ‘evolution’ to denote the historical development of life. Evolution is nothing but change. Changes within the organism over a period of time is termed ‘micro-evolution’ and changes from one being to other i.e. transformation, is termed as ‘macro-evolution’. The term evolution may be defined in several ways. Thus, we can speak of the geological evolution or evolution of planet earth, evolution of solar systems, the evolution of automobiles, radios and telephones etc. The changes involved in the rise of human civilization can be called cultural evolution

  • In the same manner, the term ‘organic evolution’ is applied where the changes that have taken place in the living things, viz. plants and animals.




  • The evolutionary thought has a very long history, from that of Aristotle to Darwin to the synthetic theory of evolution (Neo-Darwinism).

  • Aristotle was of the view that it is the inner instinct of an organism which enables them to transform towards better by adaptation. He believed that old forms of life give rise to new forms.

  • Aristotle is credited with the coining of the term ‘Anthropology’ and is hence known as the ‘Father of Anthropology’

Principles of Evolution

Image of Principles of Evolution

Image of Principles of Evolution


Image of Speciation

Image of Speciation

  • Ernst Mayr (1970) defined speciation as creation of species. It can also be defined evolution of two or more species from one. The entire evolution depends on the origins of new populations from their ancestors.

What is Species?

  • It is a group of living organism consisting of similar individual capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial.

  • According to Mayr, true speciation or multiplication of species may occur by the following agencies.

Image of speciation or multiplication of species

Image of Speciation or Multiplication of Species

  • Instantaneous Speciation: means speciation through

  • individual. An individual is responsible for creating a change in the species.

  • Genetically, there can be mutation in single gene of an asexual species resulting in instantaneous speciation.

  • By macro genesis we mean by a sudden mutation producing a heritable variation in the morphology of a species that occurs more abruptly than other instances of comparable change and is difficult to explain through natural selection.

  • In partially or wholly sexual species, cytological speciation occurs.

    • By Chromosomal Mutation that is if there is mutation among the genes of a chromosomes

    • By Polyploidy that is when the state of a cell or organism having more than two paired sets of chromosomes

  • Apart from instantaneous speciation, speciation also occurs through:

Gradual Speciation (Through Populations)

  • Geographical Speciation

  • Sympatric Speciation

  • However, the process of speciation is possible by four different mechanisms viz., allopatric, parapatric, sympatric and quantum speciation

Allopatric Speciation

  • It is also called geographic speciation. It is a key factor in speciation and a common process by which new species arise. In this scenario, the population splits into two geographically isolated populations by some geographic barrier, such as mountain range or river for terrestrial organisms, or a land mass for aquatic organism.

  • The isolated population are liable to diverge evolutionary over many generations as

    • they became subjected to dissimilar selective pressures.

    • they independently undergo genetic drift.

    • different mutations arise in the two population.

  • This is an almost exclusive mode of speciation among animals, most likely the prevailing mode even in plants. Darwin’s finches are best example for allopatric speciation.

Parapatric Speciation

Image of Parapatric Speciation

Image of Parapatric Speciation

  • In this mode, a small population enters into a new habitat, but there is a physical separation between these two sub-populations. Individuals of each species may come in contact or cross habitats from time to time.

  • Gene flow occurs between these two sub-populations. Parapatric speciation predicts that hybrid zones will often exist at junction between the two populations.

Sympatric Speciation

Image of Cichilds of Eastern African Region

Image of Cichilds of Eastern African Region

Cichlids of Eastern African Region

  • In this process of speciation, two or more descendant species are formed, from a single ancestor and these occupy same geographical locality. In this kind of speciation even a small amount of gene flow may eliminate genetic differences between parts of a population.

  • Numerous examples for this type of speciation are observed in the invertebrates.

  • Cichlids in East Africa is one of the examples and thought to be due to sexual selection.

Quantum Speciation

  • Also known as the Peripheric Speciation. Grant defined quantum speciation as “the budding off a new and very different daughter species from semi- isolated peripheral population of the ancestral species in a cross-fertilization organism.”

  • Quantum speciation is speedy and requires only few generations. The ancestors of new species do not include a large proportion of the population, and may consist of only one or few individuals.

Image of Quantum Speciation

Image of Quantum Speciation


#What is Evolution? # Principles of Evolution


# Instantaneous and Gradual Speciation

# Allopatric, Parapatric, Sympatric and Quantum Speciation

#Physical Anthropology


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