Natural Selection's Effects on Survival and Variation

Steps:

• Define natural selection as the differential survival and reproduction of individuals due to differences in phenotype.
• Evaluate first statement: better adapted species survive more offspring, so true.
• Evaluate second statement: if environmental pressures eliminate unfit individuals without suitable variants, populations can go extinct, so true.
• Evaluate third statement: natural selection acts on existing genetic variation but does not cause mutations, which arise randomly, so false.

Why A is correct:

• It accurately reflects Darwin's theory: selection favors adaptation (true), can drive unfit populations to extinction (true), but relies on pre-existing mutations rather than causing them (false).

Why the others are wrong:

• B incorrectly denies extinction risk and claims selection causes mutations.
• C wrongly states selection does not favor better-adapted survival.
• D wrongly denies both adaptation benefits and extinction potential.

Final answer: A