Often organisms seem similar in their outward appearances. For example, a porpoise and a shark seem closely related, but they are not. Such similarity is the result of .

Such similarity is the result of CONVERGENT EVOLUTION

Explanation:

Evolution can be defined as the theory that was developed based on the findings of scientists that living organisms are descended from a common ancestor.

The current theory of the process of evolution makes use of present day knowledge of genes and chromosomes to explain the source of genetic variation upon which natural selection works. It postulates that although natural selection is the only force that regularly produces adaptive evolutionary change, other forces too play a part in evolution.

Evolutionary changes may show the following patterns:

--> one species gradually transform into another species.

--> one or more species evolve as offshoots of a single ancestral species to fill a wide variety of habitat. This is known as divergent evolution.

--> Many superficially similar looking species arise from different ancestral species. This is known as CONVERGENT EVOLUTION. It is shown by organisms occupying very similar kinds of environment. That is why a porpoise and a shark seem closely related, but they are not.