In order for speciation to occur, organisms can no longer interbreed. This is known as:

• A. Genetic drift
• B. Reproductive isolation
• C. Gene flow
• D. Natural selection

Answer: (B)

Verified step by step guidance

1. Understand the concept of speciation: Speciation is the process by which populations of the same species become so genetically distinct that they can no longer interbreed and produce viable, fertile offspring.
2. Identify the key term in the question: The question mentions that organisms can no longer interbreed, which is a critical clue.
3. Review the provided options: Genetic drift, reproductive isolation, gene flow, and natural selection. Each term has a specific biological meaning.
4. Define 'reproductive isolation': Reproductive isolation occurs when populations of organisms are prevented from interbreeding due to physical, behavioral, temporal, or genetic barriers. This is a key mechanism in speciation.
5. Eliminate incorrect options: Genetic drift refers to random changes in allele frequencies, gene flow involves the transfer of alleles between populations, and natural selection is the process by which traits that improve survival and reproduction become more common. None of these directly describe the inability to interbreed, which is reproductive isolation.