What is the purpose of testing for selection versus drift across independent populations rather than a single population?

• A. To distinguish stochastic changes from adaptive ones and identify parallel evolution.
• B. To maximize the rate of drift.
• C. To avoid any evidence of selection.
• D. To measure only neutral variation.

Answer: (A)

Focusing on multiple, independent populations tests whether observed genetic changes are due to selection rather than random drift. In a single population, changes in allele frequencies could be caused by drift or selection, and it’s hard to tell which is at work. But when several populations face the same environmental pressures and show similar, directional changes at the same genetic regions, that parallel evolution is strong evidence of adaptive selection. Drift is random and tends to produce uncorrelated changes across populations, so consistent patterns across replicates point to selection rather than chance. This approach also helps separate adaptive changes from neutral variation by showing whether changes recur across independent lines under similar conditions. The other options don’t fit because maximizing drift isn’t the goal, avoiding any evidence of selection isn’t the aim, and measuring only neutral variation misses the point of distinguishing selection from drift.