When we define evolutionary relationships, we rely on

$[$Neutral$,$ Negative or Positive$]$

genetic variants because they are

$[$ Common or Rare $]$

$.$ However,

$[$Neutral$,$ Negative or Positive$]$

genetic variants are what actually drive evolution because they result in

$[$ Increased or Decreased $]$

fitness and undergo

$[$ Purifying or Positive $]$

selection in the population.