Final answer:
If Darwin's four postulates are true, evolution in a population is virtually inevitable. Natural populations are continuously subject to mutations, natural selection, and other forces that drive evolution, rendering the Hardy-Weinberg equilibrium an unrealistic scenario. Therefore, evolution is an ongoing process in most natural populations.
Step-by-step explanation:
If Darwin's four postulates are true for a given population, it is virtually inevitable that evolution will occur. These postulates address a population with variations among individuals, differential survival and reproduction due to these variations, and hereditary traits being passed to subsequent generations, ensuring that advantageous traits become more common over time. The impossibility of a population achieving the conditions for Hardy-Weinberg equilibrium, where allele frequencies do not change, implies that in the real world, populations are almost always evolving.
The Hardy-Weinberg principle is used as a baseline to identify evolutionary changes rather than to depict a real, non-evolving population. Since mutations, natural selection, genetic drift, and gene flow are continuously at play in the natural world, allele frequencies within populations are in a constant state of flux, indicating ongoing evolution. Therefore, even if the Hardy-Weinberg equilibrium were theoretically possible, the necessary absence of evolutionary forces (mutation, selection, etc.) is highly improbable in nature.
Thus, one could conclude that evolution is a constant in most, if not all, natural populations today due to the ongoing genetic variation and selective pressures they experience.