What must be present first in order for natural selection to

In order for natural selection to occur there must be a change in the environment(I.e. natural disasters, predators, food source change, etc.) and then one of two things must happen: either all
Of the organisms die out in that population, or some survive and reproduce and all of the organisms have better suited traits for their environment

The correct answer is: making up measurement to record

Amutation is basically the change in the gene, caused by alteration of single based units in the dna, or the genes or chromosomes were rearranged in the dna