Question

(i) What is natural selection ?

(ii) Explain the type of natural selection that promotes evolutionary change. Give an example.

Hint:

Natural selection favours the better adapted forms; directional selection shifts the trait in one direction, as in the peppered moth.

Answer 1

Step 1: (i) Define natural selection:
Natural selection is the process in which organisms with traits that suit their environment survive and reproduce more than others.
Their useful traits then pass to the next generation, so the population changes over time.

Step 2: (ii) Name the type:
Directional selection promotes evolutionary change.
Here the population is pushed towards one extreme of the trait, so the peak of the normal curve shifts in one direction.

Step 3: (ii) Give an example:
Before industrialisation, light coloured peppered moths were common on light tree trunks.
After industrial smoke darkened the trunks, dark moths hid better from birds, so their number rose and the light ones declined.

Final Answer:
(i) Survival and reproduction of better adapted forms. (ii) Directional selection, for example the rise of dark peppered moths in polluted areas.