Which of the following statements about reproductive barriers and speciation is true?

• A. Reproductive barriers always increase gene flow between populations.
• B. Reproductive barriers prevent gene flow between populations, leading to the formation of new species.
• C. Speciation can only occur in the absence of any reproductive barriers.
• D. Reproductive barriers are only important after two species have already formed.

Answer: (B)

Verified step by step guidance

1. Step 1: Begin by understanding the concept of reproductive barriers. Reproductive barriers are mechanisms that prevent different populations or species from interbreeding, thereby reducing or eliminating gene flow between them.
2. Step 2: Recognize the role of reproductive barriers in speciation. Speciation is the process by which new species arise, often as a result of reproductive barriers that isolate populations genetically over time.
3. Step 3: Analyze the incorrect statements in the problem. For example, 'Reproductive barriers always increase gene flow between populations' is incorrect because barriers reduce gene flow, not increase it. Similarly, 'Speciation can only occur in the absence of any reproductive barriers' is incorrect because reproductive barriers are often necessary for speciation to occur.
4. Step 4: Evaluate the statement 'Reproductive barriers prevent gene flow between populations, leading to the formation of new species.' This is correct because reproductive isolation is a key factor in the divergence of populations into distinct species.
5. Step 5: Understand why 'Reproductive barriers are only important after two species have already formed' is incorrect. Reproductive barriers are crucial during the process of speciation, not just after species formation.