Question

Fitness is the end result of the ability to adapt and get selected by nature. Explain with a suitable example.

Answer 1

When the environment changes your species has 2 options, either adapt to survive or go extinct. The ones that manage to adapt to survive, end up passing those genes into the population thus ensure that the entire future population has adapted. Thus the population looks fitter as compared to the previous version of the species.

This can be understood by the example of industrial melanism. In a collection of moths made in 1850s, i.e., before industrialisation set in, it was observed that there were more white-winged moths on trees than dark-winged or melanised moths. However, in the collection carried out from the same area, but after industrialisation, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed.

The explanation put forth for this observation was that ‘predators will spot a moth against a contrasting background’. During post- industrialisation period, the tree trunks became dark due to industrial smoke and soots. Under this condition, the white-winged moth did not survive due to predators, dark-winged or melanised moth survived. Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees – in that background the white-winged moth survived but the dark-coloured moths were picked out by predators. Hence, moths that were able to camouflage themselves, i.e., hide in the background, survived. This understanding is supported by the fact that in areas where industrialisation did not occur e.g., in rural areas, the count of melanic moths was low. This showed that in a mixed population, those that can better-adapt, survive and increase in population size.