How can a population become a new species?

A population can become a new species primarily through isolation that prevents gene flow. This isolation can occur in various forms, such as geographical separation (like mountains or water bodies) or temporal differences (like mating seasons), which effectively restricts the exchange of genes between two populations. Over time, the isolated populations can evolve independently due to different selective pressures in their environments, mutations, and genetic drift.

As each population adapts to its specific environment, they may develop distinct characteristics that prevent interbreeding when they come into contact again, resulting in reproductive isolation. This process of speciation is foundational in evolutionary biology and emphasizes the importance of genetic divergence in the formation of new species.

The other options do not adequately represent the process of speciation. For example, while increasing population size is relevant for genetic diversity, it does not initiate speciation on its own. Adapting features that are less beneficial would likely not promote survival or reproduction, undermining the tendency toward speciation. Lastly, accumulating environmental pressures equally does not account for how differences in adaptation and isolation drive the development of new species. Thus, the mechanism of isolation that prevents gene flow is crucial for the emergence of new species.