This has long fascinated scientists, but what drives the evolution of this intelligence remains “one of the most hotly debated topics in biology”, says Benjamin Ashton from the University of Bristol, UK, lead author of a paper published in the journal Nature Communications.
His team suggests that interacting with outsiders from the same species could be an important driver of brain evolution in animals, a possibility that has been largely neglected in non-human theories of intelligence.
Other theories have posited that ecological challenges, complex landscapes and avoiding predators made animals smarter. A dominating notion is that big brains evolved from social interactions involving competition and cooperation within animal groups.
But the researchers argue that the latter theory doesn’t fully explain the role of sociality in variations of brain size and intelligence between species.
“Biologists have shown how interactions with groupmates can generate ‘Machiavellian’ intelligence, the House of Cards-style cunning needed to get ahead in social politics within groups,” Ashton explains.
“We argue that animals also need ‘Napoleonic’ intelligence, the Game of Thrones-style guile necessary to triumph in a world packed with rival outsiders.”
And this added dimension makes sense, he adds.
“Outside threats and opportunities likely present a range of cognitive challenges. Animals have to defend their territories, find mates and compete for resources – we believe negotiating such challenges requires considerable brain power.”
The researchers merged their expertise in animal cognition, intergroup conflict and social evolution to propose a series of ways to test this missing link, factoring in territorial overlap, frequency of interaction and mating with outsiders and aggressive confrontations.
Observations have shown, for example, that solitary western fence lizards (Sceloporus occidentalis) have substantial overlap in their home range and territories.
Other animals like the socially monogamous, yellow-breasted chat birds (Icteria virens) have been found making night-time visits to other territories, presumably seeking mating opportunities.
Between-group competition is evidenced by fierce contests between chimpanzees (Pan troglodytes), which the authors note “can have dramatic consequences for social evolution”.
Testing the theory could include modelling brain size in relation to outsider threat and investigating cognitive variation and evolutionary benefits such as reproductive success in response to outside selection pressures.
The team says factoring outsider interactions into social intelligence theories will likely close the loop on its role in cognitive evolution.
“What do big-brained animals have in common with Napoleon Bonaparte?” asks senior author Andrew Radford. “We suspect that their ancestors possessed the intelligence to triumph in one of the highest-stakes games of all: outmanoeuvring outsiders.”