Q.54 Which of the following is a neutral phenomenon?
(A) Natural selection
(B) Sexual selection
(C) Genetic drift
(D) Population bottleneck
Genetic drift stands out as the neutral evolutionary force among the options, driven purely by random chance rather than fitness advantages. This SEO-optimized article breaks down Q.54 from evolution biology exams, highlighting why genetic drift is the correct answer.
Correct Answer
The correct answer is (C) Genetic drift. Unlike the other options, genetic drift operates without any selective pressure, relying solely on random fluctuations in allele frequencies due to sampling errors in finite populations. This makes it a cornerstone of the neutral theory of molecular evolution, where changes occur neutrally without impacting fitness.
Natural Selection Breakdown
Natural selection is a non-neutral process where environmental pressures favor individuals with advantageous traits, increasing their reproductive success and shifting allele frequencies directionally. For example, in peppered moths during industrialization, darker variants survived better against predation, demonstrating adaptive evolution. It actively shapes populations toward better fitness, ruling it out as neutral.
Sexual Selection Details
Sexual selection, a subset of natural selection, involves mate choice or competition leading to traits like peacock tails that enhance mating success but may reduce survival. This fitness-based mechanism is inherently directional and non-neutral, as it prioritizes reproductive advantages over random chance. It explains ornate features in species but not neutral evolution.
Genetic Drift Core Explanation
Genetic drift is the neutral phenomenon, causing random allele frequency changes, especially in small populations where chance events fix or eliminate alleles regardless of fitness. Its effects amplify inversely with population size—stronger in tiny groups, negligible in large ones—leading to phenomena like allele fixation over generations. This randomness distinguishes it from selection-driven processes.
Population Bottleneck Impact
A population bottleneck is a drastic, temporary reduction in population size (e.g., due to disasters), intensifying genetic drift by creating a random survivor subset with reduced genetic diversity. While it leverages drift’s neutrality, it is an event triggering drift rather than the phenomenon itself, making (D) incorrect. Cheetahs exemplify this, showing low variation from past bottlenecks.
