Multiple empirical studies confirm that one-way (unidirectional) reproductive isolation, such as asymmetric hybrid sterility or incompatibility, occurs naturally between divergent populations.
The claim posits that one-way reproductive isolation between populations occurs in nature. This is a specific, empirical, and testable claim in evolutionary biology regarding speciation mechanisms. A large number of the retrieved papers provide direct empirical evidence of unidirectional or asymmetric reproductive isolation (e.g., papers 0, 4, 5, 6, 7, and 10), demonstrating hybrid dysfunction, sterility, or cytoplasmic incompatibilities that operate in only one direction between populations or subspecies. None of the papers refute the claim; all relevant evidence supports it. Therefore, the balance verdict is SUPPORTED.