Final answer:
The stages of speciation in three-spine sticklebacks are best attributed to allopatric speciation, where geographic isolation leads to independent evolution and the formation of new species. This is a widely observed mechanism in the evolution of diverse species. OPTION B IS ANSWER
Step-by-step explanation:
The stages of speciation and evidence from natural populations such as the three-spine sticklebacks can be attributed to allopatric speciation. This is a process where a species diverges into two or more distinct species when populations become geographically isolated from one another and evolve independently due to different environmental pressures and natural selection.
For example, the Grand Canyon has served as a geographic barrier separating squirrel populations, which has led to the emergence of different squirrel species on either side of the canyon. Similarly, adaptive radiation occurs when a species rapidly diversifies into new forms to fill ecological niches, as observed in Darwin's finches.
Both allopatric speciation and adaptive radiation are natural processes that explain the origin of living systems and the diversity of life forms. It is important to note that while factors such as the bottleneck effect, convergent evolution, and adaptive radiation do play roles in evolution, in the context of three-spine sticklebacks, allopatric speciation is the key process by which speciation can be observed. OPTION B IS ANSWER