What is genetic drift?

Genetic drift is indeed defined as a change in allele frequency by chance, particularly prominent in small populations. This phenomenon occurs due to random sampling effects that can lead to fluctuations in allele frequencies from one generation to the next, independent of natural selection.

In smaller populations, the impact of genetic drift is amplified because each individual's contribution to the gene pool is more significant. Random events, such as alleles being lost or fixed, can drastically shape the genetic structure of the population over time. This randomness means that certain alleles can become either more common or rarer purely by chance, rather than being influenced by any adaptive advantage, which is where the concept of selectivity differs.

The other options relate to various biological processes but do not accurately capture the essence of genetic drift. Genetic drift is not driven by selective pressures, nor does it inherently relate to adaptations affecting reproduction. Additionally, while it can contribute to speciation over long timescales, it is not a direct mechanism for the emergence of new species on its own. Thus, the correct understanding of genetic drift revolves around its nature as a chance-based alteration in allele frequencies, especially noted in smaller populations.