Hardy-Weinberg Law: Why It Applies Only to Non-Evolving Populations

The Hardy-Weinberg law is a foundational concept in population genetics, providing the mathematical basis for understanding how allele and genotype frequencies behave in the absence of evolutionary forces. But what kind of population does this law actually describe? The answer is clear: the Hardy-Weinberg law operates only in a non-evolving population.

What Is the Hardy-Weinberg Law?

The Hardy-Weinberg law states that in a large, randomly mating population with no evolutionary influences—such as mutation, migration, selection, or genetic drift—the frequencies of alleles and genotypes will remain constant from generation to generation. This state is known as Hardy-Weinberg equilibrium.

Key Assumptions for Hardy-Weinberg Equilibrium

For a population to remain in Hardy-Weinberg equilibrium, it must meet several strict conditions:

• No Mutation: No new alleles are introduced into the gene pool.

• No Migration (Gene Flow): No individuals enter or leave the population.

• No Natural Selection: All genotypes have equal chances of survival and reproduction.

• Random Mating: Mating occurs at random, without preference for particular genotypes.

• Very Large Population Size: The population is so large that genetic drift (random changes in allele frequency) is negligible.

If any of these conditions are violated, the population will evolve, and allele frequencies will change over time, breaking the Hardy-Weinberg equilibrium.

Why Only Non-Evolving Populations?

The law provides a null model—a baseline scenario where no evolution is occurring. This allows scientists to detect when evolution is happening by comparing observed genetic data with Hardy-Weinberg predictions. If the population is evolving, one or more of the equilibrium conditions is not being met.

Why Not Other Types of Populations?

• Slow or Fast Evolving Populations: Any amount of evolution, regardless of speed, violates the Hardy-Weinberg assumptions.

• Random Evolving Populations: Evolution of any kind (random or directed) means allele frequencies are changing, so the law does not apply.

Conclusion: The Correct Answer

The Hardy-Weinberg law operates on non-evolving populations. This law is essential for understanding genetic stability and for detecting when and how evolution is occurring in real populations.

Correct answer: (1) Non-evolving population