From Storytelling to Facebook

Cultural evolution researchers use transmission chain experiments to investigate which content is more likely to survive when transmitted from one individual to another. These experiments resemble oral storytelling, wherein individuals need to understand, memorize, and reproduce the content. However, prominent contemporary forms of cultural transmission—think an online sharing—only involve the willingness to transmit the content. Here I present two fully preregistered online experiments that explicitly investigated the differences between these two modalities of transmission. The first experiment (N = 1,080 participants) examined whether negative content, information eliciting disgust, and threat-related information were better transmitted than their neutral counterpart in a traditional transmission chain setup. The second experiment (N = 1,200 participants) used the same material, but participants were asked whether or not they would share the content in two conditions: in a large anonymous social network or with their friends, in their favorite social network. Negative content was both better transmitted in transmission chain experiments and shared more than its neutral counterpart. Threat-related information was successful in transmission chain experiments but not when sharing, and finally, information eliciting disgust was not advantaged in either. Overall, the results present a composite picture, suggesting that the interactions between the specific content and the medium of transmission are important and, possibly, that content biases are stronger when memorization and reproduction are involved in the transmission—as in oral transmission—than when they are not—as in online sharing. Negative content seems to be reliably favored in both modalities of transmission. Supplementary Information The online version contains supplementary material available at 10.1007/s12110-022-09423-1.

identified in the hospital only. Chickenpox can be transmitted when a person touches another one.

Threat-related
Attractive: The FBI reported increases in the violent crime rate between 2017 and 2019. Violent crime includes offences such as rape, robbery and assault. Most of the crimes that are reported to police are not solved. This is based on an FBI measure known as the "clearance rate." In 2018, police nationwide cleared less than half of violent crimes that were reported to them.
Neutral: The FBI reported increases in corporate bribery between 2017 and 2019. Corporate bribery means giving a reward to influence someone's behaviour. Most of the bribery cases that are reported are not solved. This is based on an FBI measure known as the "clearance rate." In 2018, police nationwide cleared less than half of bribery cases that were reported to them.

Stimuli checks
To assess if there was a reliable difference between attractive and neutral stories, I tested whether attractive stories were indeed rated as more negative, electing disgust, or concerning threats than their neutral counterparts. A total of 180 participants from UK were recruited online through Prolific. Participants were pre-screened for being more than 18 years old and for reporting English as their first language. Each participant was paid 0.50£, or 15.00£/hour for an estimated completion time of 2 minutes.
Three texts, one for each content bias, were presented to each participant, in random order. For each content bias, again randomly, either the attractive or the neutral version was presented. After reading the story, the participant were asked, depending on the context bias, if they agreed with the statement "The story is negative," or "The story elicits disgust," or "The story concerns possible threats." Participants could answer using a 5-Point Likert Scale, with values (1) Strongly agree; (2) Agree; (3) Neutral; (4) Disagree; (5) Strongly disagree. The procedure, as for the main experiments, was realised with the software Qualtrics.
While to a variable degree among the three content biases (see Figure 1), in all three cases the ratings of the attractive version were significantly different, according to a Mann-Whitney U test, from the ratings of the neutral version: negative content (n 1 = n 2 = 90, U = 380, p < 0.001), information eliciting disgust (n 1 = n 2 = 90, U = 906, p < 0.001), and threat-related information (n 1 = n 2 = 90, U = 2108, p < 0.001).

Key information analysis
The analysis reported in the main manuscript for Experiment 1 focused on determining the presence or the absence of information from the full story presented to participants. An alternative strategy could be tracking only the key information, i.e. the pieces of information that distinguish the attractive and neutral material. The key information was defined as such:

Negative
Attractive: References to (i) the machine malfunctioning, (ii) that there was a legal battle (iii) that was lost Neutral: References to (i) the fact that the staff congratulated (ii) as it was the highest win

Eliciting disgust
Attractive: References to (i) faeces/toilets as the source of the outbreak Neutral: References to (i) touching another person as the mean of transmission

Threat-related
Attractive: References to (i) violent crimes, (ii) such as rape, robbery and assault Neutral: References to (i) corporate bribery, (ii) meaning giving a reward to influence someone's behaviour negative disgust threat From a visual inspection (see Figure 2), the output is consistent with the strong effect of negative content, but in this case it seems that there is also a strong effect of the key information on disgust (faeces in the hospital toilets versus a person touching another one) and less effect for the threat-related key information.

Full results of original experiments and replications
After running the original experiments, a concern was that the story related to information eliciting disgust, involving an outbreak of an infective disease (see main manuscript), could have evoked associations with the COVID-19 pandemic in the participants, possibly influencing the results.
Therefore, I tested two alternative vignettes, inspired by two of the stories used in Eriksson & Coultas (2014). In both cases, however, the transmission chain experiments did not show that the version with information eliciting disgust was more successful than the alternative (data not shown
The methods are as detailed in the main manuscript, with the difference that 60 independent chains of transmission were run for each content bias (30 with the attractive content and 30 with the neutral content), and that the analysis did not include repetition (original/replication) as random effect.
In the original experiment, confirming the predictions, the proportion of content retained remained higher for the attractive content for all three content biases (see Figure 3): negative information

Experiment 2
The second experiment involved 600 participants: 300 participants for condition 1 (76% females, M age = 34.75, SD = 11.3), and 300 participants for condition 2 (69% females, M age = 34.15, SD = 11.1). The methods are as detailed in the main manuscript, with the difference that the analysis did not include repetition (original/replication) as random effect.
The attractive content was shared more than the neutral counterpart in only one out of six possible combinations condition/content-bias, i.e. negative content in the anonymous sharing condition, The full results are as below (see Figure 4). Anonymous sharing condition: negative information

Experiment 1
For replication of the first experiment, 540 participants (63% females, M age = 36.47, SD = 12.4) were recruited. As above, the methods are as detailed in the main manuscript, with the difference that 60 independent chains of transmission were run for each content bias, and that the analysis did not include repetition (original/replication) as random effect.
In the replication (see Figure
As above, the methods are as detailed in the main manuscript, with the difference that the analysis did not include repetition (original/replication) as random effect.
In the replication, the attractive content was shared more only in the negative information/sharing with friends case (see Figure 6). The full outputs of the anonymous sharing condition were: