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The Story of Life...and Organisms

Origin of Life

  • During his exploration of the Galapagos Islands, Darwin noticed that there were many varieties of finches in the same island.

  • They varied from normal seed eating varieties to those that ate insects.

  • This process of evolution starting from a single point and radiating in different directions is called adaptive radiation.

  • The other example for this is the evolution of the Australian marsupials from a single ancestor. Placental mammals also exhibit similarities to their corresponding marsupial. Example: placental wolf and the Tasmanian wolf

  • When more than one adaptive radiation occurs in an isolated geographical area, the phenomenon is called convergent evolution.

Let us understand how evolutionary relationships can be traced using various evidences.

There is a diversity of living organisms on Earth, yet different types of organisms have some features in common.

Consider the following example:

Forelimbs of humans and wings of birds look different externally. However, their skeletal structure is similar. Thus, their origin is similar (as wings in birds are modifications of forearms), but functions are different. While wings help a bird in flight, the forearm helps human beings in various activities. These structures are called homologous structures or organs.

Homologous organs:

The homologous organs are similar in form (or are embryologically similar), but perform different functions in different organisms. The bone structure observed in wings of birds, flippers of dolphins and arms of human beings is similar, but perform different functions. They belong to the same group of animals, the vertebrates, and therefore, exhibit homology.

Now, consider the wings of a bird and an insect. They are similar in function, but this similarity does not mean that these animals are more closely related. When c…

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