Why Does Exogamy, the Practice of Seeking a Husband or Wife

Why does exogamy, the practice of seeking a husband or wife outside one's own kin group, have adaptive value outside of biological concerns?

A) It impedes peaceful relations among social groups and therefore promotes population expansion.
B) Exogamy is not adaptive; it is just a cultural construction.
C) It increases the likelihood that disadvantageous alleles will find phenotypic expression and thus be eliminated from the population.
D) It creates new social ties and alliances, providing access to more resources and social networks.
E) It was an important causal factor in the origin of social stratification.