The question of how and why the human mind evolved is among the biggest questions ever asked. Major progress has been achieved in answering how we are different from other primates, in particular chimpanzees, our closest relatives: Human children don’t differ that much with regard to particular physical cognitive skills but the gap is fundamentally social.
These differences are most apparent in socio-cognitive contexts, such as Cooperation, Communication, and Culture – the so-called big-C contexts.
Intriguingly, what underlies performance in these big-C contexts in which humans excel is bio-behavioral synchronicity: the coordination of biological and behavioral signals between interacting partners. In short, we align, and tune in with our interaction partners all the time. This ranges from heart rate synchronization to hormonal and behavioral synchronization, and even to vocal alignment.
We thus know well that the gap between apes and humans is fundamentally social.
What we do not know, however, is why this gap emerged: Why was it exactly us, rather than any of the other great apes to evolve into such a hyper-social cognitive niche?
Several answers have been proposed, and some of the most influential ones stress interdependence as key factor. Compared to other apes, humans are much more interdependent: within foraging bands, for instance, fitnesses are intertwined. This is because we critically depend on each other, with regard to our subsistence of cooperative foraging with extensive food sharing, and also with regard to child rearing: we are essentially cooperative breeders and hunters. One influential hypothesis argues this explains why our minds have evolved to be so fundamentally prosocial. The problem is that these ideas and hypotheses are reconstructions, and at best supported by correlative evidence.
The goal of ENGINE is to go beyond correlation, and experimentally investigate the consequences of increased interdependence, relying on plastic responses (“in real time”) to an increased or reduced need to cooperate. Thus, we experimentally manipulate interdependence in a colony of marmoset monkeys, to be able to assess the consequences in terms of synchronicity at various levels (hormonal, behavioral, acoustic) as well as the performance in big-C tasks.
We chose marmosets because they are renowned for their excellent socio-cognitive abilities and cooperativeness, which are necessary preconditions to make the interdependence treatment possible at all. Like humans, they cooperate extensively, in particular when rearing offspring. Furthermore like humans, they tune in with each other, and synchronize at the hormonal, behavioral, and even vocal level.
What really sets this project apart from previous approaches is thus that we are able to experimentally measure the consequences that arise when a primate lives either an independent or a highly interdependent lifestyle, which corresponds to the evolutionary contrast between the independent lifestyle of our chimpanzee-like ancestors and the obligate interdependence of modern humans. First and foremost, this will critically advance our understanding of the evolutionary origin of the human mind. But beyond that, our results may also have profound implications for general wellbeing and public mental health if it turns out that interdependence – or its loss in modern societies – has critical downstream effects.
