The article says "inbreeding" isn't all bad, despite popular notions...
If acted upon by natural selection, bad mutations can be wiped out more easily, thus speeding the rate of evolution. And for some reason, third- and fourth-cousins that marry each other in Iceland have more children.But what about the fruit flies?
When given a choice between a brother or a non-brother, females preferred mating with their brother. But, males did not prefer their sister. They simply tolerated mating with their sister, picking them roughly half the time. Similarly, females showed no preference when choosing between their father or a non-father, picking their dad about 50% of the time. Males wooed their moms, but no successful mating occurred.
The authors conclude that inbreeding occurs in fruit flies because it may increase their inclusive fitness.
Source: Loyau A, Cornuau JH, Clobert J, Danchin É (2012). "Incestuous Sisters: Mate Preference for Brothers over Unrelated Males in Drosophila melanogaster." PLoS ONE 7(12): e51293. doi:10.1371/journal.pone.0051293
The information is extensive, complete with many references. It is good reading for those of you who enjoy scientific journals.
We investigated male and female mate preferences with respect to relatedness in the fruit fly D. melanogaster. Experiments offered the choice between a first order relative (full-sibling or parent) and an unrelated individual with the same age and mating history. We found that females significantly preferred mating with their brothers, thus supporting inbreeding preference. Moreover, females did not avoid mating with their fathers, and males did not avoid mating with their sisters, thus supporting inbreeding tolerance. Our experiments therefore add empirical evidence for inbreeding preference, which strengthens the prediction that inbreeding tolerance and preference can evolve under specific circumstances through the positive effects on inclusive fitness.