Haldane's rule

[4] Hybrid dysfunction (sterility and inviability) is a major form of post-zygotic reproductive isolation, which occurs in early stages of speciation.

[7] The main genetic hypotheses are: Data from multiple phylogenetic groups support a combination of dominance and faster X-chromosome theories.

[9] However, it has recently been argued that dominance theory can not explain Haldane's rule in marsupials since both sexes experience the same incompatibilities due to paternal X-inactivation in females.

[10] The dominance hypothesis is the core of the composite theory, and X-linked recessive/dominance effects have been demonstrated in many cases to cause hybrid incompatibilities.

For example, a significant reduction of male-driven gene flow is observed in Asian elephants, suggesting faster evolution of male traits.