Across human cultures the world over, indulging in sexual relations or marriages up to a certain relationship degrees are considered taboo. These taboo sexual acts or relationships, like between brother and sister, Father and daughter, mother and son, with someone in the same Family tree (up to four or five generations in paternal or maternal side)are normally called incest and are forbidden by societies since time immemorial. Any aberration to this rule, if existed in ancient civilizations like Incas, Romans etc; has nearly been wiped out by now. The main reasons for stopping humans from these taboo relationships, is to stop inbreeding. The reasons why inbreeding was so cautioned against was that Inbreeding produces the potential for a reduced gene pool, higher levels of genetic disorders (in the offspring), and an overall reduction in species viability over time. In short, if the whole objective of mating is to increase the chances of survival of any specie through successive generations(humans included), then Inbreeding reduces the Chances.
That said, although prohibition to inbreeding is practiced by human societies quite stringently through age old customs and traditions; not much research is being done on "How living world (humans, insects, animals) don't inbreed, even when there are no social restrictiveness or law forbidding them. In other words, "what stops people in close relations (blood relations etc.) from attracting towards each other in such a manner that they inbreed?". A research, a year ago revealed that a lot of childhood bodily touch (kissing and cuddling) between a Parent & a child OR childhood wrestling between siblings; makes them Not see each other as potential mate during adulthood. But still such studies are quite scarce.
A new unique experiment by Erik van Bergen, at the University of Cambridge, that determined how female butterflies avoid breeding with inbred male butterflies in the March 5, 2013, issue of the journal Proceedings of the Royal Society B; can be called one of the few scientifically documented researches, which sheds light on "natural means of inbreeding avoidance".
The Research:
For the study the researchers used a butterfly species Bicyclus anynana. This particular butterfly specie has to ensure its survival, more than others, as 50 percent of inbred males are sterile.
The researchers purposefully bred a group of inbred males. The genitals of the inbred males and outbred males were coated with different colored fluorescent dyes to track which group were more attractive to a group of female butterflies that included the sisters of the inbred male group. Deposits of the dyes on the female were indicative of attraction.
Some of the female butterflies had their antennae covered with nail polish to prevent female reception of sex pheromone produced by males (so that they are not affected by the Pheromones).
The researchers found that female butterflies of this species preferentially mated with outbred males if the females were able to detect the male sex pheromone. Inbred males produced a lower level of the sex pheromone and were less likely to be selected as mates by the female butterflies.
The phenomenon is assumed to be species independent and common across all species of butterflies.
Conclusion: Rather than anything, inbreeding avoidance is intrinsic.
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