At the risk of being the setup man for shots from genetics experts, here are a few comments as they relate to ORCHID breeding. Mother nature deals with plentitude and genetic diversity to assure the survival of species, by means of pollinators carry pollen from one flower to flowers of another plant. In fact some species have mechanisms which prevent self-pollination or at least make it difficult.
Although breeders generally recognize the inherent risks of self pollination, sometimes, there is no alternative to selfing a plant in cultivation. In some cases, only one or a few plants of a species were discovered. In order to propagate a plant, selfing was necessary. In many more common cases, breeders may have had only one plant (not necessarily the original) to work with. Carried out over generations, some species,consequently, may become less vigorous and prone to disease or other afflictions. For these very reasons, in most contemporary human societies, marriage between closely related individuals is either prohibited or discouraged.
While continued selfing of successive generations might lead to less variation, this is not necessarily a good thing. I have seen certain species (line bred for generations) develop a reputation for being, weak, non-vigorous and difficult to bloom. Then when a specimen of the same species was aquired, from jungle seed or close to a natural source (with its non-depleted gene pool) the offspring grew and bloomed much more vigorously under the same cultural conditions.
Sometimes, the term "species A x sibling" is not used properly. "species A x sibling" would mean that a plant has been crossed to a same generation member of the same seed batch (brother and sister, if you will). However, if 2 unrelated plants of the same species are crossed, they should be designated as "species A x species A". For ease of designation, sometimes a cross between 2 unrelated plants of the same species is incorrectly designated as "species A x sibling".
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