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Understanding Biological Evolution

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Evolution and Adaptation

The processes of natural selection and heredity together result in an organism inheriting more of those characteristics or traits or features or behavior which make the organism better fitted or suited for survival in its natural environment. This is known as Adaptation.

Some common examples of adaptation are –

  1. water birds developed longer beaks to hunt for fish in the water
  2. giraffes grew longer necks to feed on the tops of trees
  3. flying birds have lighter bones to allow flight
  4. aquatic fish and mammals have streamlined bodies for movement in the water
  5. some insects developed to look like the leaf of a tree to evade predators
  6. bats developed echolocation to catch insects

Heredity is the mechanism by which these characteristics, traits, features and behaviors are passed on through genes from one generation to the next.

Introduction to Evolution

The formation and development of life on earth is the process of Evolution. It is a process by which all organisms have descended from some common ancient ancestors. However, evolution is an imperfect process – if it were a completely perfect process, all living organisms today would look exactly the same as the one-celled organism from which they have all evolved!

In other words, this Descent occurs with modifications – Genetic Variations in living matter that are the very foundation of evolution.

Two processes – Natural Selection and Heredity – govern evolution.

Natural Selection determines which species (or members of a species) survive to pass on their characteristics and traits to the next generation. This is popularly referred to as the “survival of the fittest”.

Evolution is responsible for all the similarities and also the diversities that we see in life. These similarities and diversities occur through the Mechanisms of Evolution. Some of these are mechanisms explained below.

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Genetic Drift

Evolutionary change can take place by random due to luck or chance. If in a population of green and brown beetles, more of the green beetles were significantly reduced by a random or chance occurrence, then the subsequent generations in that population would have more brown beetles than green.

Differential Reproductive Success

If green beetles were to get eaten more than brown beetles simply due to their attractive color, then subsequent generations in that population would have more brown beetles than green. This, again, is the basis of natural selection or survival of the fittest.


The DNA duplication process in green beetles might undergo a change or a Mutation, as a result of which the gene that is responsible for green coloration is changed or altered to brown. This is a loss of genetic information, resulting in green beetles then having only brown offspring.


The development of new or distinct species through such mechanisms of evolutionary change is termed Speciation– the emergence of new species.

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Human Impact on Speciation

A relatively recent phenomenon in human history has been the impact of human life on a variety of species. Humans have been responsible for several species completely disappearing from the planet. Several of them were hunted for meat, such as the dodo, the passenger pigeon, and the Steller’s sea cow. Close to 800 species have been documented that have been driven to extinction between around 1500 AD and now. There may be many more species that existed and which we are not even aware of!

Human impact on climate due to high fossil fuel usage has resulted in warmer temperatures, rising sea levels, longer summers, variations in rainfall etc. This is also affecting many species in various ways. Many species may relocate or migrate to cooler regions. Many will need to adapt to new environments, triggering more evolutionary changes. Many could simply die out. Recent reports indicate that a million or more species could be threatened with extinction in the coming decades.

A lesser-studied aspect of human activities is the impact on new speciation. Humans have domesticated several species, leading to their increased populations. Humans have occupied or created new ecosystems, enabling several species to migrate and flourish in those regions. In recent years there has been global attention on conservation, leading to the protection of threatened species. And so on.

Clearly though, the destructive impact of human existence far outweighs the positive aspects.

Check Point

  1. Genetic variations are the very foundation of ______.
  2. Two major processes governing evolution are ______ and ______.
  3. The inheritance of features that make an organism better suited for survival in its natural environment is termed as ______.
  4. Name three mechanisms of evolution.
  5. Identify three human activities responsible for impacting species.

Answer Key

  1. Evolution
  2. Natural Selection, Heredity
  3. Adaptation
  4. Mutation, Genetic Drift, Differential Reproductive Success
  5. Hunting, fossil fuel usage, inhabiting new territories, domesticating species

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Images Credit: University of California Museum of Paleontology’s Understanding Evolution

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