Different content biases affect fidelity of disease transmission along experimental diffusion chains

Although many theoretical studies have investigated which social learning biases are involved in the diffusion of information in human groups, many of these biases are still unknown. We investigated, for the first time, whether factors such as ancestry, regularity in evolutionary time, regularity in the current environment, and previous experience with health conditions act as biases along experimental transmission chains. We performed an experiment based on recall products from 80 chains of four generations each (N = 320). The content transmitted between the participants involved fictional stories containing information about different diseases (causes, symptoms, and forms of treatment) grouped according to their regularity in evolutionary time (acute or chronic), regularity in the current environment (high incidence or low incidence), period of origin (ancestral or modern), and previous experience (yes or no). The stories were passed along the linear chains of four participants who read and recalled them, and the product of their recall was passed on to the next participant within their chain. As predicted, we found that information about ancestral and more regularly affecting diseases throughout human (acute) evolutionary history acted as content biases, guiding the more accurate diffusion of information. In contrast, we found no evidence to support the influence of context biases for regularity in the current environment (high-incidence diseases) and from previous experiences when these were simulated along the experimental transmission chains. We argue that content bias may have driven the biased dissemination of information about ancestral and acute diseases. Acute illnesses were more regular over evolutionary time and may have generated greater selective pressure on human cognition. Furthermore, our behavioral immune systems may have evolved to respond more efficiently to clues to diseases we have faced thousands of years ago than clues to recent illnesses. This fact may have led to information about ancestral diseases becoming more memorable and better diffused in experimental cultural chains.