But for the interests of science, researchers have come to the conclusion that yes, inbreeding really does lead to stupidity.
A team from University of Edinburgh has found that animals that are inbred make mistakes in response to changes in their surroundings.
The serious implication, however, is that it might threaten their very survival.
To illustrate their thinking, a lab found inbred beetles were more likely to make bad decisions amid developing circumstances, at a cost to themselves and their offspring. The findings could inform now conservation programmes and aid the understanding of wild animals.
It could allow environmentalists to adjust the way they act in deploying strategies to counter the effects of depopulation within species.
And that would prove especially useful in areas where shrinking populations raises the likelihood of inbreeding – which in turn causes more problems.
Researchers from the university observed hundreds of female burying beetles as they raised their offspring.
They spent thousands of hours watching how they behaved. Midway through the experiment, researchers swapped the resources available to each female.
They chose to switch out a dead mouse on which they feed their young for another of a different size.
Inbred females whose mouse was swapped for a smaller one failed to adjust their parenting strategy.
That slow response meant that they raised too many young with not enough food.
As a result, their young were smaller and the mother lost weight. The results meaning all were less likely to breed in future.
Parents that were not inbred, however, responded.
The chose to cope with the unexpected loss of resources by culling some of their young.
That is what scientsist expected would be their natural response in the wild in similar circumstances.
The inbred animals’ lack of response to changes may be down to impaired thinking ability or lack of sensitivity to their surroundings, suggest researchers.
Previous studies had shown that the effects of being inbred – which can impact on growth, survival, or chances of reproduction – can be worsened by environmental conditions.
The latest study shows that bad decision-making by individuals plays a part in this effect.
Jon Richardson, of the university’s School of Biological Sciences, who led the study, said there was no doubt that there was a corrolation.
He said: “The impact of environmental conditions can amplify the effects of being inbred, such as susceptibility to disease or competing for resources.
“We now know that poor decision-making plays a part in the burden facing inbred animals.”
The study, published in Proceedings of the Royal Society B, was supported by the Natural Environment Research Council.