It is often assumed among laypersons that inbreeding of organisms is inevitably negative and hybridization always produces increased vigor. Not the case. In fact, our understanding of the genetic underpinnings of fitness is not particularly strong, especially in honey bees. It is currently thought that "diversity" is beneficial, but obviously there is more to it than that.

> Hybridization between populations or species can have either beneficial or detrimental effects on fitness. If these effects could be predicted based on the genetic or geographical distance between parents, this would be of great use to plant and animal breeders, managers and conservation biologists. The divergence times resulting in hybrid vigor, outbreeding depression or partial reproductive compatibility vary widely both within and among taxonomic groups.

> Hybridization has been used to induce HYBRID VIGOR in domesticated plants and animals since before Darwin, and translocation between natural populations is increasingly being proposed as a management tool with which to bolster dwindling population sizes and to prevent INBREEDING DEPRESSION. However, enthusiasm for this management method is tempered by concerns about OUTBREEDING DEPRESSION.

> Most studies quantifying mean hybrid fitness in known generations have stopped at the F1, with a few extending to the and one study showing that outbreeding depression was not apparent until the F3. Beyond this, hybrid fitness might continue to decline as recombination further disrupts tight linkages, or it might increase and possibly surpass parental fitness as selection promotes beneficial gene combinations. 

> The likelihood of these alternative scenarios is related, in part, to the number and linkage relationships of genes underlying hybrid incompatibility; thus, a better understanding of the duration of outbreeding depression awaits both long-term hybridization experiments and further studies of the genetic architecture of speciation.

Does parental divergence predict reproductive compatibility? 
Suzanne Edmands. TRENDS in Ecology & Evolution. 2002
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