What could cause unrelated species to resemble each other over generations?

The resemblance of unrelated species over generations can often be attributed to similar environmental factors. When different species inhabit similar environments, they may adapt to comparable challenges and opportunities provided by that environment, leading to convergent evolution. This process results in the evolution of similar traits or features in species that do not share a recent common ancestor.

For example, animals such as dolphins (mammals) and sharks (fish) both possess streamlined bodies and fins suitable for swimming in the ocean, despite being from entirely different evolutionary backgrounds. The environmental pressures of living in aquatic environments have shaped their body plans in similar ways, facilitating efficient movement through water.

Overall, it is the shared environmental influences that drive the similarity seen among unrelated species, illustrating how adaptation to similar ecological niches can lead to analogous structures and forms across different lineages.