Final answer:
To determine if evolution is happening, scientists compare actual genetic data to expected frequencies from the Hardy-Weinberg formula. Deviations indicate evolutionary forces at play and help measure microevolutionary shifts.
Step-by-step explanation:
To determine if evolution is occurring in a population using the Hardy-Weinberg formula, one must compare actual observed genetic data from a population to the expected frequencies calculated using the Hardy-Weinberg principle. The principle assumes no evolution occurs if a population meets five criteria: no mutations, no gene flow (migration), random mating, no genetic drift, and no selection. The formula, p² + 2pq + q² = 1, predicts the expected frequencies of alleles (p and q) and genotypes in a population at genetic equilibrium.
When actual genetic data deviates from these predictions, it suggests that one or more of the Hardy-Weinberg conditions are not met, indicating evolutionary forces may be at work. These forces include mutation, natural selection, genetic drift, and migration. For example, if a gene for pesticide resistance rises in frequency after pesticide use, this would suggest selection is favoring resistant individuals, and the population is evolving.
Scientists use this comparison to measure microevolutionary shifts and to infer which evolutionary forces are influencing the population. Deviations from Hardy-Weinberg equilibrium parameters can pinpoint the specific evolutionary processes occurring within the gene pool of the population.