The excessive use of herbicides, pesticides etc. has resulted in selection of resistant varieties. It is an example of evolution by:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Anthropogenic action
Option (1) Natural selection — Incorrect. Selection does act here, but NCERT names this case by its cause: the selecting force is human use of chemicals.
Option (2) Chemical action — Incorrect. Herbicides and pesticides were the agents used, but the change is not caused by the chemicals acting on the genes. The chemicals only picked out resistant varieties, and the cause of their use is human activity, so NCERT calls this evolution by anthropogenic action.
Option (3) Mutation — Incorrect. The chemicals did not create the resistance; they picked out resistant variants already present.
Option (4) Anthropogenic action — Correct. Resistant forms appear within months or years, not centuries.
NCERT Extract:
Mechanism of Evolution – “… Similarly, excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell. Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries. These are examples of evolution by anthropogenic action.”