Sometimes an evolutionary change produced in an organism for one purpose later on becomes more useful for an entirely different function. For example, birds evolved feathers as a means of providing insulation to their bodies in cold weather but later on these feathers became more useful for the purpose of flying.
Even some dinosaurs had feathers though they could not fly by using these feathers. Birds, however, adapted feathers for flying. The presence of feathers on birds tells us that the birds are very closely related to reptiles because dinosaurs (which had feathers) were reptiles.
In the evidence for evolution we have studied that very dissimilar looking structures can evolve from a common ancestral body design. But that was all guesswork about what happened in history long time ago. We will now give an example from the present time which will show that different looking organisms can in fact be created from the same basic design of the ancestor.
The wild cabbage plant is a good example to prove that entirely different looking organisms can evolve] from the same organism by the process of evolution. The only difference is that here we are using artificially selection for evolution in place of natural selection. This will become clear from the following discussion.
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The farmers have been cultivating wild cabbage as a food plant for over two thousand years and have produced (or evolved) entirely different looking vegetables like cabbage, broccoli, cauliflower, kohlrabi and kale from it by artificial selection.
(ii) When farmers opted for the arrested flower development of wild cabbage plant, it led to the production of another variety of cabbage called ‘broccoli’.
(iii) Some farmers went in for sterile flowers of wild cabbage and developed another variety of cabbage called ‘cauliflower’.
(iv) When farmers opted for the swollen parts of wild cabbage, it led to the evolution of a yet another variety of cabbage called ‘kohlrabi’.
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(v)And finally, the farmers wanted to grow large leaves of wild cabbage and ended up producing a leafy vegetable called ‘kale’ which is also a variety of wild cabbage.
Now, wild cabbage is the ancestor and cabbage, broccoli, cauliflower, kohlrabi and kale are all its varieties which have been obtained by evolution ‘induced artificially’ by the farmers.
The ordinary cabbage, broccoli, cauliflower, kohlrabi and kale look so different from their ancestor wild cabbage that if people had not seen it being done with their own eyes, they would never have believed that vegetables having such different structures can be evolved from the same ancestral vegetable plant.