Feb 09,2007 00:00
Breeding between close kin is thought to be fraught with evolutionary pitfalls: it tends to saddle offspring with dangerous levels of genetic defects.
In some species, “close inbreeding may be explained by relatives being better parents,” Timo Thünken and colleagues of the University of Bonn, Germany, wrote in the Feb. 6 issue of the research journal Current Biology.
Parenting costs energy, and kinship tends to favor cooperation. Indeed, observations of this fish showed that related parents “were more cooperative and invested more” in parenting, the scientists wrote. The reason, they added, is likely that a male mating with his sister ensures that his young receive extra copies of his genes—from their mother. That would promote his own evolutionary success.
So inbreeding isn’t uniformly bad, Thünken and colleagues wrote: evolutionarily speaking, “an individual has to trade off the costs against the benefits” of it.
The main drawback is that inbreeding can bring together couples with the same gene defects. The mutations are often harmless in them because there are back-up copies of the genes. But inbreeding parents can pool the mutations in offspring, overwhelming the backup systems.
There was no evidence of this occurring in the fish, Thünken and colleagues wrote, for unclear reasons. Perhaps good parenting made up for bad genes, they speculated. Another possibility, they wrote, is a possible self-correcting mechanism tied to inbreeding. Theorists believe that repeated inbreeding may lead to die-offs of badly mutated individuals. That “purges” the population’s bad genes, staving off genetic disintegration.