It is richly ironic that were the scandal to lead news corp to sell its uk papers , and some of them were to prove inviable in new ownership , such plurality could be another casualty of this affair .
One of the main obstacles is that , even if members of different species might mate , when the two species are too distant genetically or carry different numbers of chromosomes , the offspring are usually inviable or infertile ( like zorses and mules ) , and are therefore evolutionary dead ends .
Individuals crossing exclusively within the same population produce more progeny than those crossing in both directions and thereby use up some of their gametes for the production of inviable hybrids .