How did some stickleback populations come to live exclusively in freshwater environments?

• A. They became isolated in freshwater lakes and adapted to the new environment through natural selection.
• B. They migrated to freshwater habitats to escape predators, but did not undergo any evolutionary changes.
• C. They were unable to survive in saltwater due to a sudden genetic mutation that made them intolerant to salt.
• D. They were artificially introduced into freshwater by humans and did not experience any natural selection.

Answer: (A)

Verified step by step guidance

1. Understand the concept of natural selection: Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce more successfully. This leads to evolutionary changes over generations.
2. Recognize the role of isolation: When populations of organisms become geographically isolated, such as sticklebacks in freshwater lakes, they are exposed to different environmental pressures compared to their original habitat.
3. Identify the environmental pressures in freshwater: Freshwater environments differ from saltwater in terms of salinity, predators, food availability, and other ecological factors. These pressures can drive adaptations in isolated populations.
4. Explain the process of adaptation: Over time, genetic variations that confer advantages in the freshwater environment (e.g., tolerance to low salinity, changes in body structure) become more common in the population through natural selection.
5. Conclude the evolutionary outcome: The stickleback populations that became isolated in freshwater lakes adapted to their new environment through natural selection, leading to the development of traits suited for freshwater living.