Question

why is variation beneficial to the species but not necessary for the individual ??

Answer 1

because variations combine and form a change in thousands of years and an individual has not such a huge life span

Answer 2

Heya mate
The answer of ur question is

♢ Variations are beneficial to the species than individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. 

For example, if the temperature of water increases suddenly, then most of the bacteria living in that water would die.

♢♢Only few variants that are resistant to heat would be able to survive.

☆☆However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species.
 However, all variations are not necessarily beneficial for the individual organisms.

hope it helps