(a) Natural selection operates when nature selects for fitness. Explain.
(b) The rate of appearance of new forms in linked to the life span of an organism.
Explain with the help of a suitable example.

Explanation

(a) Natural resources are limited, populations are stable in size, members of a population vary in characteristics even though they look superficially similar. Theoretically, population will increase exponentially but the population size in reality is limited thus leading to competition. Only the ones which are fit and adapt themselves are able to survive. They grow at the cost of others and flourish. This was called as natural selection by Darwin.
(b) According to Darwin, the fitness of an organism is measured by its reproductive ability.
Also the appearance of new forms is linked to the life span of an organism. The greater its lifespan, the more it can reproduce and hence, greater new forms would appear. This can be observed in the Development of dark-winged moth due to industrial melanism.
For example, industrial evidence : It is a case of natural selection. In England, it was observed before industrialisation that white-winged moth were more than dark-winged moth. But the situation became reversed after industrialisation. It was found that predators will spot and pick a moth against a contrasting background.
During pre-industrialisation, the tree trunks were covered by white lichens and on white- background dark coloured moth can be picked up, During post industrialisation, the tree trunks were covered by dark, dust, coal particles and became dark, on which white moth can easily be picked up. Thus, it was found that industrial melanism supports evolution by natural selection.