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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 carefully observed, the wings of a bird and an insect are not similar. Such organs, which have similar functions in different organisms (but are not closely related), are known as analogous organs.

Analogous organs:

The organs that perform similar functions in different organisms of different origins are analogous. For example, wings of birds and wings of insects; fins of fishes and flippers of whales; wings of birds and wings of bats (bird wings are made of feathers, while bat wings are folds of skin) all exhibit analogy. Both are used for flight, but they are structurally different. Also, they are found in organisms which are not related.

Do you know that genetic fingerprinting or DNA testing (using samples of DNA) can distinguish individuals of the same species? This technique is used in forensic science laboratories to analyze samples of blood, hair, and saliva.

Fossils as an evidence of evolution

What are fossils?

A group of students went for trekking. After a tiresome day, when they dug the ground to pitch their tents, one of them discovered skeletal remains of a dead animal inside the ground. They examined it closely to find out which animal the skeletal belonged to. However, surprisingly, the features of the skeletal remains resembled more than one animal. Later, when they took it to a lab for examination, they discovered that the remains were of an ancestral reptile, as old as 1000 years!

Let us explore more about fossils.

Fossils are the remains of organisms that once existed on Earth. They represent the ancestors of plants and animals, which are alive even today.

Fossils provide evidences of evolution by revealing the characteristics of the past organisms, and the changes that have occurred in these organisms to give rise to a present organism.

Appearance of fossils

Fossils have the same shape as that …

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