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Evolution may be partly to blame for autoimmune diseases such as rheumatoid arthritis, new research suggests.

Scientists have found that gene variants linked to the autoimmune disease may have brought about a survival advantage in humans that prevented these 'faulty' genes from being bred out by natural selection.

Researchers at Stanford University's School of Medicine conducted a genetic study which revealed that several mutations associated with an increased risk of rheumatoid arthritis had been increasing in prevalence.

Usually, versions of genes that cause disease or premature death are selected out under the process of natural selection, because affected individuals tend to be less likely to have children and pass on the mutation. However, the research suggests that, in order to increase in prevalence, the mutations for rheumatoid arthritis must have conferred enough of an advantage to ensure they were passed on to new generations.

According to the research article, which is published in the Public Library of Science One, one possibility is that the faulty genes may have provided our ancestors with some protection against certain viruses or bacteria, such as tuberculosis. The study authors wrote: "There is a stark correlation between populations having higher incidence of tuberculosis also having lower incidence of rheumatoid arthritis, and vice versa.

"It has been speculated that genetic variants enhancing resistance to tuberculosis underwent positive selection and provide the genetic basis for rheumatoid arthritis susceptibility today. Our analysis is completely compatible with this theory."