Final answer:
The best scenario supporting the Red Queen Hypothesis is b, where an asexually reproducing snail population dies out due to a parasite invasion. This demonstrates the advantage of sexual reproduction in providing genetic diversity that is crucial for evolutionary adaptation and survival against rapidly evolving threats such as parasites.
Step-by-step explanation:
The best support for the Red Queen Hypothesis is scenario b. Individuals of a snail population that reproduce asexually die out after a parasite invades its territory. This hypothesis suggests that sex helps hosts evolve fast enough to maintain their defenses against the rapid evolution of parasites and other coevolving entities. The snail population's lack of genetic variation, a consequence of asexual reproduction, would have handicapped its ability to adapt to the new parasitic threat, leading to its demise.
In more general terms, sexual reproduction produces genetic variability which, in turn, accelerates evolutionary adaptation. This is essential to counteract the rapid evolution of organisms that a species may interact with, such as predators, parasites, and competitors. In the snail's case, this variability was insufficient to survive the parasite's evolution. Such a situation validates the Red Queen Hypothesis' core idea: species must continuously evolve, “running” just to stay in the same place or to maintain equilibrium with their coevolving counterparts. The genetic diversity produced by sex is a crucial mechanism that provides a buffer against extinction when faced with relentless evolutionary pressure.