Heredity and Evolution: Meaning of Evolution, Human Evolution, History of Evolutionary Thought (For CBSE, ICSE, IAS, NET, NRA 2022)

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Meaning of Evolution

  • It is the change in the heritable characteristics of biological populations over successive generations.
  • During reproduction, these characteristics are passed on from parent to offspring.
  • The process of evolution has given rise to:
    • Biodiversity at every level of biological organization.
    • Levels of species.
    • Individual organisms and molecules.
  • Through change sin heritable traits, Evolution in organisms occur.
    • For example, eye colour is an inherited characteristic.
    • An individual might inherit the “brown-eye trait” from one of their parents.

Charles Darwin

He is also known as the “Father of Evolution” and was an English Naturalist and Biologist.

Evolution of Life

  • It is believed that the Prokaryotes inhabited the Earth from approximately 3 – 4 billion years ago.
  • Between 1.6 – 2.7 billion years ago, the eukaryotic cells emerged.
  • plants and fungi colonised the land and were soon followed by arthropods and other animals about 500 million years ago.

Human Evolution

  • Humans belong to the primate family.
  • Ancestors of Humans include:
    • Dryopithecus
    • Ramapithecus
    • Australopithecus
    • Homo erectus
    • Homo sapiens
    • Cro-magnon man

History of Evolutionary Thought

Classical Times

One type of organism could descend from another type.


All-natural things as actualisations of fixed natural possibilities were considered by Aristotelianism.


  • The Aristotelian approach was rejected by the new method of modern science in the 17th century.
  • Explanations of natural phenomena in terms of physical laws.
  • The hierarchical nature of species relationships was explicitly recognized by biological classification introduced by Carl Linnaeus in 1735.

Darwinian Revolution

  • He believed that population growth would lead to a “struggle for existence” .
  • Charles Darwin in 1842 penned the first sketch of the Origin of Species.

Pangenesis and Heredity

  • Gregor Mendel in 1865 proposed that the traits were inherited in a predictable manner through:
    • Independent assortment.
    • Segregation of elements (later known as genes) .
  • Most of Darwin՚s pangenesis theory was supplanted by the Mendel՚s laws of inheritance.

The ‘Modern Synthesis’

  • It connected natural selection and population genetics in the 1920s and 1930s.
  • The patterns observed across species in populations was explained by the modern synthesis.
  • Advancements were also made in:
    • Phylogenetic systematics.
    • Mapping the transition of traits into a comparative and testable framework.

Further Syntheses

The biological phenomena across the full and integrative scale of the biological hierarchy starting from genes to species.


  • The process that makes organisms better suited to their habitat.
  • It can be further referred to a trait that is important for an organism՚s survival.
  • One of the best examples is that of the adaptation of horses՚ teeth to the grinding of grass.
  • Adaptation may cause:
    • Either the gain of a new feature.
    • Or the loss of an ancestral feature.
Homologous Bones in the Limbs of Tetrapods


  • Both conflict and cooperation can be produced due to the interactions between organisms.
  • In a second species, the evolution of one species causes adaptations.
  • Thus, the cycle of selection and response is called coevolution.
  • For example, the production of tetrodotoxin in the rough-skinned newt.


It is the process where a species diverges into two or more descendant species.


Spatial Aspects of Speciation

Spatial Aspects of Speciation

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