They insist that when you take reproduction out of the equation through birth control, sterilization, or homosexuality, no one is harmed by incest.
Of course, the law has something to say about that.
Females are more heavily invested invested in the genetic fitness of their offspring, and experts believe that’s why women tend to be particularly averse to incest.
A 1994 study showed that women might actually be able to smell the best genetic mate to father their future offspring.
This preference for the “new guy” forces young male hyenas to leave their families upon adulthood in search of a pack of unrelated females, resulting in low levels of inbreeding among the species. The estimated 500-percent growth of the bedbug population in recent years was partially caused by a chemical resistance to insecticides but also the bedbug’s ability to thrive on inbreeding.
When bedbugs that have this resistance to insecticide continue to inbreed, doubling up on those resistant genes strengthens the resistence of the next generation, making the parasites even harder to kill and demonstrating one of the few instances in which inbreeding can actually benefit a species.
Most animals suffer the same adverse effects from inbreeding as humans, such as reduced fertility, slower growth rates, increased incidence of disease, and higher mortality rates.
Because hyenas don’t use scent or other cues to identify relatives, females only mate with males that are new to their group.
Female lemurs, for instance, can tell if a male’s genes are too similar to her own by smelling the pheromones that emit from his genitals.
Mice also use smell to identify ideal potential mates, much like the human females in the smelly t-shirt test.
Experiments have shown that keeping a brother and sister mouse isolated in a cage will often result in their mating, but only if there are no other viable partners.
Introducing an unrelated male compels the female to abandon her brother.