A new study has suggested that baboons can solve abstract reasoning problems using cognitive tools previously thought, among primates, to be solely the reserve of humans.
The study, publishing in Psychological Science by researchers at Harvard University, Carnegie Mellon University and Yale University, showed that olive baboons (Papio anubis) could make use of a logical argument called disjunctive syllogism, which previously was thought to require language.
In jargon-free terms a disjunctive syllogism is a logical argument centered around an “or” statement, from which we can derive meaning. For example:
There are only two types of bird in my garden: sparrows or bluetits. The bird I am looking at is not a bluetit, so it must therefore be a sparrow.
The cup test
In humans, the ability to use disjunctive syllogism to make decisions has been extensively studied. Research examining young children has shown that they appear to develop this ability around the age of two. One classical experiment involves hiding a reward under one of two cups and then showing the participant that one cup has nothing under it. Those studies held that, if the participant then checked under the second cup to find the treat, that would be an example of using disjunctive reasoning.
The authors of the current study, Harvard’s Dr Stephen Ferrigno, Yale’s Dr Yiyun Huang and Carnegie Mellon’s Dr Jessica Cantlon, pointed out a flaw in that previous study design: the participants could just be checking under the cup out of hope or curiosity, rather than a logical certainty that it held the rewards they were looking for.
A newer test design seemed to fix these flaws: children were presented with two pairs of two cups, with one cup in each pair containing a reward. After the experimenters removed one cup, showing it didn’t contain a reward, the children then were allowed to choose a second cup to look under. If the kids were using deductive logic – the first cup they checked had no reward, so its pair cup must have one - they would be more likely to choose the empty cup’s pair. If they were guessing randomly, any of the three remaining cups would be potential choices. This updated task showed that humans can’t reason though disjunctive syllogism until they are between three and five years old.
The authors of the current study put a group of monkeys up to the four-cup reasoning test, with unexpected results. The participants, a troop of nine adult baboons, were trained in how to participate in the experiment – whilst the children in the previous study were rewarded with stickers, the baboons were hunting for grapes – and four proved capable of understanding the rules of the game.
The study’s results showed that the baboons were indeed capable of using disjunctive syllogism to reason – they were much more likely to pick the empty cup’s pair than a cup from the other set. With three cups to pick from, if the baboons had been choosing randomly, it would be expected that 33% of the time, they would pick the pair cup that had to contain a grape. Instead, the four baboons on average picked that cup 58% of the time.
The baboons, the authored noted, seemed to automatically know the location of the grape once the empty cup had been lifted – immediately pointing at the paired cup even before the experimenter had prompted them to choose.
The study found that disjunctive syllogism isn’t unique to humans and doesn’t require a linguistic understanding of an either/or scenario. The baboons join humans and a single African gray parrot named Griffin as the only animals thus far capable of this feat.