how do variations promote survival?

Dear student,

During a change in environmental conditions, organisms showing resistance to the condition have a chance of survival whereas all other organisms of the species would perish.

For example, if there were a population of bacteria living in temperate waters, and if the water temperature were to be increased by global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time.