From The Righteous Mind: Why Good People Are Divided by Politics and Religion, by Jonathan Haidt

In 49 BCE, Gaius Julius made the momentous decision to cross the Rubicon, a shallow river in northern Italy. He broke Roman law (which forbade generals to approach Rome with their armies), started a civil war, and became Julius Caesar, the absolute ruler of Rome. He also gave us a metaphor for any small action that sets in motion an unstoppable train of events with momentous consequences. It’s great fun to look back at history and identify Rubicon crossings. I used to believe that there were too many small steps in the evolution of morality to identify one as the Rubicon, but I changed my mind when I heard Michael Tomasello, one of the world’s foremost experts on chimpanzee cognition, utter this sentence: “It is inconceivable that you would ever see two chimpanzees carrying a log together.” 52 I was stunned. Chimps are arguably the second-smartest species on the planet, able to make tools, learn sign language, predict the intentions of other chimps, and deceive each other to get what they want. As individuals, they’re brilliant. So why can’t they work together? What are they missing? (pp 208-209)

According to Tomasello, human cognition veered away from that of other primates when our ancestors developed shared intentionality . 54 At some point in the last million years, a small group of our ancestors developed the ability to share mental representations of tasks that two or more of them were pursuing together. For example, while foraging, one person pulls down a branch while the other plucks the fruit, and they both share the meal. Chimps never do this. Or while hunting, the pair splits up to approach an animal from both sides. Chimps sometimes appear to do this, as in the widely reported cases of chimps hunting colobus monkeys, 55 but Tomasello argues that the chimps are not really working together. Rather, each chimp is surveying the scene and then taking the action that seems best to him at that moment. 56 Tomasello notes that these monkey hunts are the only time that chimps seem to be working together, yet even in these rare cases they fail to show the signs of real cooperation. They make no effort to communicate with each other, for example, and they are terrible at sharing the spoils among the hunters, each of whom must use force to obtain a share of meat at the end. They all chase the monkey at the same time, yet they don’t all seem to be on the same page about the hunt.

In contrast, when early humans began to share intentions, their ability to hunt, gather, raise children, and raid their neighbors increased exponentially. Everyone on the team now had a mental representation of the task, knew that his or her partners shared the same representation, knew when a partner had acted in a way that impeded success or that hogged the spoils, and reacted negatively to such violations. When everyone in a group began to share a common understanding of how things were supposed to be done, and then felt a flash of negativity when any individual violated those expectations, the first moral matrix was born. 57 (Remember that a matrix is a consensual hallucination.) That, I believe, was our Rubicon crossing. (pp 210-211)

FIGURE 9.1. Time line of major events in human evolution . MYA = million years ago; KYA = thousand years ago. Dates drawn from Potts and Sloan 2010; Richerson and Boyd 2005; and Tattersall 2009. (p. 212)

The Rubicon crossing that let our ancestors function so well in their groups was the emergence of the uniquely human ability to share intentions and other mental representations. This ability enabled early humans to collaborate, divide labor, and develop shared norms for judging each other’s behavior. These shared norms were the beginning of the moral matrices that govern our social lives today. (p. 225)