Variations in an individual may be an advantage or disadvantage for it. It may enable or disable it to cope with changes in the environment. Advantageous variations are selected by environmental factors.
For example bacteria that can withstand heat will survive better in a heat wave. Such heritable variations lead to the evolution and formation of new species.
An advantage of sexual reproduction is that the variations accumulated in the gametes of each sex are combined when they fuse to form the zygote.
Hence an offspring produced from the zygote receives and carries the variations of both the parents. On the other hand, in asexual reproduction there are minor differences among the offspring. These are due to small errors in DNA copying. As gametes and zygote formation are not involves the asexually produced offspring are quite similar. They have fewer variations accumulated over generations.
