Supplementary information from The coevolution of cooperation and cognition in humans

This file includes additional methods, supplementary tables and figures

Supplementary information from The coevolution of cooperation and cognition in humans

This file includes additional methods, supplementary tables and figures

A summary of the game show procedure showing the distribution of balls and players by round, along with when certain variables were observed and recorded.

<p>The following text is a brief glossary followed by detailed description of each round. <b>Golden balls</b>: the ‘golden’ spheres that contain either cash values inside (‘£££’) or the word ‘killer’, in which case they are a ‘killer ball’. <b>- £££ Cash balls:</b> range in value from £10 to £75,000. <b>- Killer balls:</b> have no positive value and are very damaging because they each reduce the current prize fund by 90% if they end up in the final selection. <b>Stakes:</b> the final prize fund, derived from 5 randomly selected balls in the final round. <b>Maximum-stakes</b>: the maximum possible prize-fund available at the start of the final round, calculated from the 5 most valuable balls in the final round. <b>Round 1:</b> The game starts with 12 cash balls and 4 killer balls. Each contestant receives four balls at random, and must place two, at random, on the ‘Front Row’, which is public and keeps two on the ‘Back Row’, which is private. In this hypothetical example, Contestant 4 has received two killer balls on her front row and Contestant 1 has one killer ball, therefore one of the eight private balls must be a killer ball. The four contestants each show their public balls, and then take turns declaring their private balls, where they are free to lie. The contestants then each vote one contestant off from the game. The evicted contestant leaves the game, along with their four golden balls, which are ‘binned’. The best outcome for the group is to eliminate the contestant with the ‘worst’ balls. After the votes have been counted, each contestant must show the true value of their private balls, this way any liars are exposed. <b>Round 2:</b> The 12 balls remaining from Round 1 are carried through to Round 2, where they are mixed with an extra three balls, to provide a total of 15 golden balls that are randomly distributed once more. Once again the contestants declare the value of their private balls, and once again are free to lie, before voting eliminates another contestant and their balls. We only analysed lying behavior in this round. <b>Final:</b> The two surviving contestants and their 10 balls enter the final, where they are accompanied by one additional killer ball. The contestants are clearly told what the maximum prize fund possible is (Maximum-stakes) before selecting five of the 11 golden balls at random to determine their final prize-fund (Stakes). <b>Negotiation:</b> After the prize-fund has been determined, the two contestants are given some time (typically under 1 minute) to discuss and negotiate their decision in the simultaneous prisoners' dilemma. <b>PD - Split or Steal:</b> the contestants now play a mini-game, which resembles the prisoners' dilemma and is referred to by the show as “Split or Steal” (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033344#pone-0033344-t001" target="_blank">Table 1</a> for payoff details).</p

The proportion of splitting across series and depending on the sex of a contestant and the sex of their opponent.

<p>How contestants responded to their opponent's sex depended on their own sex and the series. Males (on the right) from different series behaved similarly but females (on the left) from later series were more cooperative to females and less cooperative to males compared to females from earlier seasons.</p

The payoff matrix for the final decision in the game show.

<p>The payoffs refer to ‘ALL’ the prize-fund, ‘HALF’ the prize-fund, or ‘ZERO’, i.e. £0.</p><p>The payoffs conform to a <i>weak</i> prisoner's dilemma, whereby to STEAL pays better or at least as well as to SPLIT, regardless of what one's opponent chooses.</p

Logistic regression plot of the probability of a contestant splitting depending upon the value of the prize fund (Stakes).

<p>The probability of a contestant splitting decreased with larger stakes. The equation for the fitted response to the prize fund held the Maximal possible prize fund constant at the mean value of £40,324. The data have been separated, to improve visualization, by a process of shifting slightly from their true positions to slightly above 0 or slightly below 1.</p

Binary logistic generalized linear model on the probability of Split versus Steal (N = 286, with errors clustered to 143 episodes).

1<p>Older contestants were more likely to SPLIT.</p>2<p>Males were more likely to SPLIT with geographically distant opponents.</p>3<p>Over time, females became both more likely to SPLIT with females and less likely to SPLIT with males, males showed no change over time.</p>4<p>STEALING was more likely as stakes increased but SPLITTING was more likely as the loss in potential winnings was increased.</p>5<p>Promising was a reliable cue of increased probability of SPLITTING.</p>6<p>Initiating laughter was a reliable cue of increased probability of SPLITTING.</p>7<p>Touching was a reliable cue of STEALING, and being touched induced STEALING.</p>8<p>Touching may only be a reliable cue of STEALING for males.</p

The proportion of splitting depending on whether a contestant initiated physical contact and/or whether their opponent initiated contact during the final two stages of the show.

<p>Contestants that were not involved in any physical contact were more likely to split than contestants that either initiated contact or were merely the receivers of such contact.</p

Experimental results

Excel spreadsheet showing raw results from all 4 experiments on colony formation in Chlorella vulgaris described in the manuscrip

Simulation code: Conditions for the expected local frequency of helpers to increase.

This is c++ code which was used to produce simulation data presented in Figure 3