Which factor within a population could be studied to determine whether the population is evolving?

One key factor that can be studied to determine if a population is evolving is the allele frequency of specific genes within that population over time. Changes in allele frequencies, particularly in response to environmental pressures or mutations, can indicate evolutionary processes such as natural selection, genetic drift, or gene flow. Additionally, observing phenotypic variations and reproductive success among individuals can provide insights into the adaptive changes occurring in the population.