Ques- branching descent and natural selection are the two key concepts of darwins theory of evolution.

      explain each concept with the help of suitable example. [CBSE 2011, 3 MARKS]

According to Darwin's theory of evolution,

Natural selection may be defined as the process by which the organisms which are better adaptive to a particular kind of environment tends to survive, leading in the elimination of the organism less adaptive to that environment. These organisms are naturally selected and reproduce to pass on their genetic qualities suitable to that environment making their species best suitable to that particular environment. An example of natural selection is that of peppered moth. Originally, the peppered moth had light coloration as it camouflaged them against the light colored trees. During industrial revolution, there was widespread pollution which led to the deposition of black soot on the tree barks. So, this led to a decrease in the population of light colored moths as they were easily visible on dark trees. At the same time, the population of dark colored moths increased as they were better suited to that environment.  

Branching descent may be defined as the process by which new species originate from a single common descendant. This can be demonstrated like a tree of life where two new organisms’ branch out from a single common ancestor, further branching keeps on taking place from those new organisms formed. When these new organisms formed from a common ancestor becomes geographically isolated and becomes a lot different from each other and becomes adapted to a particular kind of environment, it results in the formation of a new species.  The given figure represents an example of branching descent where species 1 is the common ancestor and over the course of time different species developed from it.