People have evolved to be superstitious because it pays to take a "better safe than sorry" approach to life, a new mathematical study suggests.
Researchers at Harvard University say history has taught people that it is better to interpret a rustle in the undergrowth as a threat just in case it is a bear, a member of a rival tribe or another real danger.
Although in the vast majority of cases it will be nothing of the sort, responding to the potential threat by always acting to ensure we protect ourselves remains the best strategy as it means we will not be caught out when the danger is real.
"In an uncertain world, natural selection can readily favour making all kinds of associations, including many incorrect ones, in order to make sure that the really important associations are made," says Dr Kevin Foster of the Centre for Systems Biology, Harvard University, near Boston, Massachusetts.
"Perhaps the easiest example to understand is the use of medicines that are not proven scientifically to actually work," explains Dr Foster, who reports the study with Dr Hanna Kokko of the University of Helsinki in the Proceedings of the Royal Society, Biological Sciences. "This occurs both in small-scale societies and in our own societies in the form of alternative medicine.
"It is clear that many medicines in these contexts do not work, but some do," says Dr Foster.
"Therefore, it may be evolutionarily advantageous to adopt the general strategy "believe that alternative medicines work" because in doing so, one will benefit from the few that are effective and suffer little cost from using those that do not work."
He adds that humans are not alone and that many other creatures are superstitious too. "Any decision making organism faces the same challenges of identifying causal relations, that is, will event A mean that event B is coming soon?
In the case of a prey species fleeing from loud noises, "it is clearly advantageous to run from all sorts of loud noises - including many that are not associated with predators - to make sure that when a predator comes, they are in a burrow or other such safe place."
The results are clear: superstitions are a part of adaptive behaviour in all organisms as they struggle to make sense of an uncertain world.
Dr Foster emphasised that the evolution of superstition is more than the natural selection of genes that linked with touching wood, crossing fingers and other superstitious traits.
"We are heavily affected by culture and learning as well, and so the specifics of any one example of superstition in humans will be affected by these factors as well."
By Roger Highfield
This article first appeared in the Telegraph.