CBSE Class 10 Answered

Variation occurs when one gene in the organism is mutated.If it allows the organism to survive longer than the others in the population without the mutation, it gives the mutated organism a higher chance to pass on its genes. When these genes are passed on, their kids may have the mutation but they will carry the mutated gene. As long as this helps the organism survive it will continue to be passed on to the next generation. After many generations, the mutated trait becomes common which means they have evolved.

Example- For example, a population of long beaks inhabit a particular area. Now, the food can be consumed properly with short beaks. If due to some variations, there may be a possibility that there are some birds with short beaks in that population. So, in the new area, they will survive better and reproduce more which will lead to the evolution of more and new species.

II. Variations is useful for the survival of species because:

1. Variation acts as a source of raw material for evolution of species.

2. Variation leads to genetic diversity, which is a key for the evolution of species. Animals are able to adapt themselves to the changing environment by inheriting some of the beneficial variations. Organisms are better suited to face the struggle for existence due to the presence of variations.

3. Variations give the species an individuality of their own. In the absence of variation, there would be no science of heredity as all individuals of a race, would be identical to one another in all aspects.

All the variants, however, do not have equal chances of survival. Depending on the environmental conditions, the nature favours only those variants that are able to adjust to the changing environment. The theory of natural selection favours the survival of the fittest.