Final answer:
A change in genotype frequency does indicate that evolution has occurred, as evolution in population genetics is defined by changes in allele frequencies over time. Factors such as genetic drift and natural selection can lead to these changes, which can be studied using the Hardy-Weinberg principle as a baseline.
Step-by-step explanation:
A change in genotype frequency over time does imply that evolution has occurred, contrary to the statement claiming that evolution has not occurred just because the frequency of the heterozygotes is different 5 years later compared with the original population. Evolution, as defined in population genetics, involves changes in a population's allele frequencies over time. This means that any changes in the frequency of alleles, including those that lead to different proportions of heterozygous individuals, are evidence of evolution. This can result from several factors, including natural selection, genetic drift, migration, and mutation. It's important to distinguish between these causes, as genetic drift refers to random changes in allele frequencies that may not lead to adaptations or improved fitness, whereas natural selection involves changes that do confer some advantage to the population.
According to the Hardy-Weinberg principle, allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences. Thus, if the frequencies are changing, this suggests that the population is not in equilibrium and is, indeed, evolving. It doesn't necessarily matter whether the change is in favor of heterozygotes or any other genotype; the fact that there is change is indicative of evolution. The Hardy-Weinberg equation serves as a mathematical baseline to compare against actual populations to deduce what evolutionary processes might be at play.