There are two different species of toads which are separated by a hot and dry valley, and fossil evidence indicates that these two species share a common ancestor. What would have caused these two species to evolve?

Adaptive Speciation

Explanation:

The two species evolved as s result of adaptive Speciation.

Adaptive speciation occurs when biological interactions induce disruptive selection and the evolution of assortative mating, thus triggering the splitting

understanding processes of adaptive speciation, in which the splitting of lineages is an adaptation caused by frequency-dependent selection. Adaptive, or sympatric, speciation has been modeled since the 1960s.

adaptive speciation

Explanation:

In evolutionary biology, adaptive radiation/speciation is a process that makes living organisms diversify and change rapidly from an ancestral species into several new forms, especially when a change or natural event in their environment makes new resources available, thereby creating new challenges and opening new environmental niches.

b.
the standard of living varies across the region.