Whilst there is lots of evidence to show that ecological conditions can provide strong selection pressures for increased cognitive abilities, they are not sufficient to explain the high intelligence observed in some of the cleverest species. Rainforests are home to 50% of the worlds animals and yet very few of these exhibit cognitive capacities comparable with those of chimps. Sharks share many habitats with dolphins and yet only the latter have a relative brain size similar to our own. What then, is responsible for the intelligence of these ‘smart animals’? It was Jolly (1966) who first put forward the idea of social intelligence, after studying the social behavior of lemurs. She suggested that species that live in tight social groups would require a high cognitive capacity in order to navigate a complicated social landscape. Several studies have investigated the relationship between neo-cortex volume and group size and have found positive correlation (Dunbar 2003), seemingly supporting this theory.
Animals live in groups for a number of reasons, such as reducing their risk of predation and improved foraging efficiency (either by working as a group or by the social transmission of information). However, group living also has costs, mainly in the form of competition. In the same way that networking and knowing the right people can help us to be more successful, forming alliances with specific individuals, as well as knowing who to avoid, can also improve the fitness of animals and reduce the costs of competition (Silk 2007).
Being able to recognize other individuals is the first step of successful socializing, as all of us will have experienced when starting a new school or job. Whilst this may seem fairly basic, it is actually quite a complex feat involving the combination of multiple sensory signals to form a mental representation of another individual. In animals, it can be difficult to distinguish between discrimination and true recognition for example, ‘that’s a large male, I’d better avoid him’ vs. ‘Bob is the dominant male, I’d better avoid him’. To overcome this, expectation violation experiments are commonly used.
For example, Proops et al. (2009) used an expectation violation experiment to test for true recognition in horses. He lead one member of a herd over the brow of a hill so that it was out of sight. He then played back the call of either the removed horse or another individual to the remaining herd members. When the call of another horse was played back, the rest of the group responded more strongly, showing that they realized that the call being played was not that of the removed individual.
Once individual recognition is possible, it is beneficial to be able to work out existing relationships and any social hierarchies present. Whilst this can be achieved using personal experience alone, it is both time consuming and potentially dangerous. It is therefore better to be able to infer hierarchies by watching the interactions and behaviors of others.
The film ‘Mean Girls’ illustrates this point rather well, with naive new girl ‘Cady’ being quickly enlightened by her new friends to as who she should and shouldn’t talk to, thus avoiding potential social embarrassment. In animals, this has been demonstrated by Paz y Mino et al. (2007) in their work with pinyon jays, a highly social member of the crow family. Observer birds were allowed to watch the dominance displays of other birds, some of which were familiar (to the observer) and some of which were strangers. When placed with unfamiliar birds, the observer used the behavior of the familiar bird (and their own relationship to this bird) to work out whether they should behave dominantly or submissively to the stranger.
Once relationships have been formed within a group it is important to both maintain them and to use them to their maximum benefit. This may involve cooperation, deception, reconciliation and manipulation. Following aggressive behavior between two individuals or groups, reconciliation will often occur, helping to restore previous alliances and to reduce stress levels. Whilst in most species reconciliation tends to occur between the primary individuals involved in the fight, in social birds, such as rooks, individuals will seek reconciliation with their long term mate. Some of the most intelligent birds, for example corvids and parrots, form lifelong pair bonds and this would perhaps suggest that the intensity of a relationship, as well as the number, is important in the social intelligence hypothesis.
Cooperation between individuals to allow the completion of tasks that would otherwise be impossible is another benefit of group living. Cooperation was demonstrated in young chimpanzees by Crawford in 1937. The chimps were given a task whereby they had to pull two ends of a rope to remove a food item from a shelf. They had the option of either attempting it alone or releasing a companion to help. When the chimps could reach both ends of the rope themselves they did not enlist help. However, when the two ends were too far apart, they first released their companion and then completed the task as a team, sharing the reward. This demonstrates that the chimps knew when cooperation was necessary but also that they act selfishly, only sharing food with their companion when their help was needed.
A core component of the social intelligence hypothesis, and perhaps also the most controversial, is that of Theory of Mind. This is the ability to recognize the fact that other individuals have a mind that controls their behavior and to imagine what they might be thinking. Whilst evidence suggests that most monkeys only have 1 intentionality level i.e. ‘I want this food’, in more intelligent animals such as chimps, this may extend to level 2 i.e. ‘I think Jenny knows where the food is’. Children acquire this ability at age 4-5 and as adults, most of us have at least 4 levels of intentionality. This allows the potential for deception, perfectly demonstrated by the game of poker where the most successful players are the ones that can best read the intentions of others and subsequently lie and bluff about their own hand. This has also been observed in several animal species. For example, subordinate male baboons have been observed leading females out of sight of the dominant male in order to groom them, whilst subordinate chimps are more likely to retrieve hidden food when they know the dominant is unaware of its presence (Hare et al. 2001).
Scrub jays cache food and pilfering of caches by others can be a major problem. When forced to cache in the presence of others, the jays will often go back alone and move their hoard to a new location in order to prevent theft. Interestingly, it is only birds that have experience of pilfering themselves that perform this behavior, suggesting that it takes a thief to know a thief (Emery and Clayton 2001).
As mentioned previously, the maintenance of social bonds is a vital part of group living and in many social animals, this takes the form of grooming. However, grooming is time consuming and demanding. In his work, Dunbar (2003) calculated that a maximum of 20% of waking hours could be allocated to grooming before detrimental costs occurred, thus limiting the number of social bonds that an individual could maintain. This percentage accurately predicts the sizes of social groups observed in primates. However, when this was extrapolated to modern humans, the group sizes predicted were far smaller than those observed. What then, allowed our ancestors to form and maintain such large social groups, arguable a key factor in our evolution?
A feasible suggestion is that of language. The use of verbal communication allows us to socialize with several individuals at once, as well as to multitask i.e. we can walk and talk at the same time. Additionally, it makes it possible for us to catch up on events we’ve missed so that we can better keep track of social changes. Looking at the fossil record, the dates predicted for the evolution of language coincide with increases in group sizes and conveniently, the average amount of time we spend per day in conversation with others is 20% (Dunbar 2003). Taking this into account, the feasible number of personal relationships that one individual could maintain is 150. This also just happens to be the number of friends the average person has on Facebook. This therefore suggests that the maintenance of social bonds was (and is) a key factor in the sizes of the communities we form and that selection for increased group sizes could have lead to the evolution of language.
Once language evolved, the potential for more complex social behavior increased, perhaps resulting in the formation of religions as well as art and music. Another potential consequence is that of increased pro-sociality or altruism i.e. a willingness to help others, even when they are unrelated, due to the enforcement of social rules and the punishment of rule breakers. Therefore, although it is likely that ecological conditions were initially responsible for the formation of close social groups, it was probably selection for increased social intelligence that lead to our large brain size and the complex societies and cultures seen today.
Dunbar, R. (2003). The Social Brain: Mind, Language, and Society in Evolutionary Perspective
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Silk, J. (2007). The adaptive value of sociality in mammalian groups Philosophical Transactions of the Royal Society B: Biological Sciences, 362 (1480), 539-559 DOI: 10.1098/rstb.2006.1994
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