Reasoning about probabilities is something humans can't always manage especially well, but it's clearly a skill we're capable of. In the wider world of animals, however, there are very few species we can say are able to make choices based on probabilities. So far, the only animals that have demonstrated the ability to make choices based on statistics are our fellow primates and the kea, an alpine parrot from New Zealand.
All the species where this ability had been seen have a large brain relative to their body size, a feature that is associated with many advanced cognitive capabilities. So it was reasonable to conclude that statistical reasoning required some significant mental horsepower. But a new study indicates that managing probabilities may be substantially more widespread than we think since an animal with a relatively small brain - the giraffe - is apparently capable of it.
For the study, four giraffes at Barcelona Zoo were shown two transparent boxes containing carrots, which they love, and courgettes, which they like less. One box contained mainly carrots, the other mainly courgettes. In front of the giraffes, a researcher reached into each box at the same time, and disguised what they had picked up in their closed fists. They then presented their fist to the animals.
Although the giraffes could not know what each hand was holding, they consistently chose the one that had been in the mainly carrot box. The team believes the giraffes had assessed the probabilities, and worked out that this hand was more likely to be holding a carrot. They theorise that in the wild, the ability to determine the proportion of leaves and flowers on a distant tree could give giraffes an evolutionary advantage.
The striking thing about this experiment is that giraffes are notable for having fairly small heads on top of enormous bodies. By one measure of relative brain size called an "encephalization quotient," they weigh in at 0.64, while the primates and parrots that are known to engage in probabilistic reasoning all have quotients more than double that. So if mental capacity were simply a matter of relative brain size, we'd expect giraffes to be lightweights. Yet they performed about as well as chimps do in these tests.