Read the passage given below and answer the following question.
Evolution by natural selection, in a true sense, would have started when cellular forms of life with differences in metabolic capability originated on earth. The essence of Darwinian theory about evolution is natural selection. The rate of appearance of new forms is linked to the life cycle or the life span. Microbes that divide fast have the ability to multiply and become millions of individuals within hours. A colony of bacteria (say A) growing on a given medium has built-in variation in terms of ability to utilise a feed component. A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions. In due course of time this variant population outgrows the others and appears as new species. This would happen within days. For the same thing to happen in a fish or fowl would take millions of years as life spans of these animals are in years. Here we say that fitness of B is better than that of A under the new conditions. Nature selects for fitness.
Excess use of herbicides and pesticides has resulted in selection of resistant varieties in a much lesser time scale. What does this tell us about evolution?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → It is a stochastic process based on chance events in nature and chance mutation in the organisms.
Heavy use of herbicides and pesticides kills the sensitive organisms, while the few that already carry resistance survive and multiply. Man has only speeded up the selection; he has not decided which organism would turn out to be resistant.
Option (1) It is a stochastic process based on chance events in nature and chance mutation in the organisms. — Correct. The resistance comes from a chance mutation that was already present in a few organisms. The heavy use of the chemical only let those few survive and multiply.
Option (2) It is a directed process in the sense of determinism. — Incorrect. NCERT says the opposite: evolution is not a directed process in the sense of determinism. Nothing fixes in advance which variety will win.
Option (3) It is driven by the use and disuse of organs in the organisms. — Incorrect. Use and disuse of organs was Lamarck’s idea, as in his giraffe example. Nobody believes it any more, and it has nothing to do with resistance to a chemical.
Option (4) It is a process in which the chemical itself produces the resistance character in the organisms. — Incorrect. The chemical does not create resistance. It only selects the organisms that were already resistant.
NCERT Extract:
What are the Evidences for 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. This also tells us that evolution is not a directed process in the sense of determinism. It is a stochastic process based on chance events in nature and chance mutation in the organisms.”