In a new study published by the journal Genome Research, a team of scientists reports that 'mad cow'-like diseases have not been a major force in human history, nor have been cannibalistic rituals that are known to be associated with disease transmission. Prof. Jaume Bertranpetit, a scientist at the Universitat Pompeu Fabra, and his colleagues used a fresh set of genetic data to show that balancing selection associated with cannibalism has not been a major selective driving force on the prion protein gene, as has recently been proposed. Their work also has important scientific implications for researchers using a specific class of DNA markers called SNPs (single nucleotide polymorphisms) to examine genetic associations with diseases or to evaluate historical patterns of human migration.