Why does the survival of species depend more on populations than on the life spans of individual organisms

The survival of a species depends more on the population because a population contains many type of organisms of the same species. Some of them are better adapted to survive the conditions provided by the Earth and hence, they live and produce offsprings with the favourable traits. The members of a population which are not better adapted mostly do not survive.

Hence, the survival of a species depends on the population where it is living.