Organisms change over time. Some of these changes make no difference to the success or failure of the organisms that inherit them; other changes do. Take a group of antelopes in which one individual has longer legs than its siblings. Those longer legs make the individual better at escaping from predators, hence giving it an advantage in the survival stakes. Its descendants inherit this feature and are better able to survive as a consequence. Those longer legs have thus become an 'adaptation'. Their evolution means that this particular lineage of antelopes has adapted to its conditions, thanks to its development of this feature.
Over the generations, the individual components of the genetic code within a species change, or mutate. So far as we know, mutations may provide no evolutionary advantage at all. They may be disadvantageous, in which case they are weeded out via natural selection; or they may be advantageous, in which case they persist through the generations.
Why do some mutations persist through generations?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → They are advantageous to the animal
The passage ends: mutations may be advantageous, "in which case they persist through the generations". The longer legs of the antelope are the example: they give it an advantage in survival, so its descendants inherit them.
Why the Other Options are Incorrect?
Option 1: They are harmful to the animal — Incorrect. Contradicted: harmful (disadvantageous) mutations are weeded out by natural selection; they do not persist.
Option 2: They make no difference to the animal's survival — Incorrect. Wrong link: the passage says that changes which make no difference exist, but it links persisting through the generations to advantageous mutations.
Option 3: They are ornamental — Incorrect. Not mentioned: ornamental means serving only as decoration; the passage says nothing of the kind.