Final answer:
Not every allele that increases in frequency is adaptive. Allele frequencies can change due to non-adaptive mechanisms like genetic drift. Adaptive evolution tends to increase beneficial alleles that contribute to fitness.
Step-by-step explanation:
Is Every Allele That Increases in Frequency Adaptive?
Not every allele that increases in frequency within a population is necessarily adaptive. While adaptive evolution does lead to an increase in the frequency of beneficial alleles and a decrease in deleterious alleles due to selection, other mechanisms can alter allele frequencies without being adaptive. For instance, genetic drift could result in an increase in allelic frequency purely by chance, especially in smaller populations through events like the bottleneck effect or the founder effect.
Natural selection, on the other hand, typically increases the frequency of alleles that offer an advantage in survival or reproduction, contributing to evolutionary fitness. The classic case study of the peppered moth's changes in wing coloration in response to industrial soot and the subsequent reversal with improved environmental conditions illustrates how natural selection drives adaptive changes in allele frequencies.
Other factors, such as assortative mating and frequency-dependent selection, can also influence allele frequencies. These mechanisms do not always lead to adaptations beneficial for survival and reproduction. Therefore, it is important to consider the full ecological and genetic context when interpreting changes in allele frequency.