Which of the following cases best illustrates speciation from a common ancestor?

Question

A single species of snails colonize a newly formed marshland formed by a retreating glacier. Over several thousand years different groups of the snails are separated geographically and are no longer able to breed and produce fertile offspring.

A small colony of cliff-dwelling birds that feeds on tree-bark beetles is marooned on a flat terrain island with only small plants and low bushes and adapts to the meadow-shrub environment.

Rabbits, which did not exist as native Australian wildlife, were introduced into the island continent, where they quickly established themselves, and now threaten to displace native marsupial species.

A population of a large turkey-like bird species takes up residence in an isolated mountain meadow with no predators and lush food supply. Over many generations the birds lose the ability to fly.

Answer 1

The case that best illustrates speciation from a common ancestor is:

A single species of snails colonizes a newly formed marshland formed by a retreating glacier. Over several thousand years, different groups of the snails are separated geographically and are no longer able to breed and produce fertile offspring.

This scenario describes allopatric speciation, which occurs when populations of a single species become geographically isolated from one another. Over time, the isolated populations can diverge genetically, leading to the development of distinct species that can no longer interbreed. This process is a key mechanism of speciation.