Final answer:
The statement about transformational and variational models of evolution being true reflects the differences in how species may evolve in uniform versus varied environments. Transformational focuses on species well-adapted to a stable environment, while variational emphasizes genetic diversity's role in adapting to environmental changes.
Step-by-step explanation:
The statement that transformational assumes essential species and a uniform environment while variational assumes that variant members of a species respond differently to environmental challenges is true. In a uniform environment, species with well-adapted traits can flourish, as assumed by transformational evolution. In contrast, variational evolution accounts for the fact that different members of a species will have varying responses to environmental pressures due to genetic diversity, increasing the likelihood of some members having advantageous traits in new environments.
For instance, in the scenario where there is a sudden and significant change in the environment, such as a volcanic eruption that divides a population, genetic diversity can be more important for the survival and evolution of species, as proposed in variational evolution. This supports the idea that Genus B, with greater genetic diversity, might have an advantage in the new environment as opposed to Genus A, which contains well-adapted species to a specific environment that no longer exists.
Concepts of Speciation
In gradual speciation, species diverge slowly as traits change progressively. However, in a punctuated equilibrium, species diverge rapidly and then remain stable for long periods. The false statement in the given scenarios would be one that contradicts these recognized patterns of speciation.
Selection pressures, like diversifying selection, can cause an increase in genetic variance by favoring multiple distinct phenotypes. This contrasts with scenarios where a fit phenotype remains unchanged in a stable environment.