This month, a paper was published in Nature Ecology & Evolution that was of immense importance to this website. In this post I will only comment on the paper itself, but I expect its data and supplementary files to be the subject of several more posts when I can obtain access to them. This material may even make it possible, for the first time ever, to generate an objective scale of cetacean intelligence. You can read the background the genesis of that paper HERE.
Unfortunately, this paper is steeped in the Machiavellian Intelligence hypothesis, which they refer to as the ‘social brain hypothesis’. Oddly, they actually do manage to find a group size correlation with behavioural complexity, but only if they used a quadratic fit. Their fit was one that I would particularly want to prove correct, as it made those cetaceans in mid-sized groups, such as killer whales and sperm whales, the smartest. Unfortunately, one of the metrics they use in their mix is social skills, and solitary animals can’t display these for field observation, even if, under extraordinary circumstances, they had the greater capacity to acquire them! For an alternative commentary on whether their findings really do support the Machiavellian Intelligence Hypothesis read HERE.
For our purpose, a more important finding in this paper, is that absolute brain size is more important than encephalisation quotients at predicting social complexity. The most exciting part is that I believe this dataset allows a test of whether an interspecific general intelligence factor exists for cetaceans. Reader et al. have already shown it possible to demonstrate the existence of g from a large and diverse set of field observations in the case of primates.
If a general intelligence factor is established for the cetacean order, probable z scores for the value of g could be estimated for each species. We would then have two mammalian orders with established intelligence scales. Although their existence would not imply that both general factors had a similar nature, it is my contention that the the case of the bottlenose dolphin provides prima facie evidence for exactly that. This cetacean species is probably the only one for which we have tested skills on many different dimensions (eg. numeric, logical inference, communication, abstract reasoning, cooperation, puzzle solving, mirror self-recognition, and others), all of which fit into a similar position (+1.5 < primate equivalent z < +2), on the primate scale.
Even if we did not have sufficient data currently to test whether interspecific g exists for cetaceans, there should still be sufficient data to calculate such scores if we just assume its presence. Our next problem would then be how to align the two scales. There are several different ways that we may attempt to do so. We could use the few species that we can place by direct testing, such as the bottlenose dolphin. We could normalise using Suzan Herculano-Houzel’s hypothesis, that total forebrain neuron count is the best physical metric for predicting intelligence differences among vertebrates. We could even try assuming that the same observed behaviour, such as the presence of prosocial activity or group feeding activity, held the same threshold values for general intelligence in both groups. All three methods should be used (and others I haven’t thought of yet), using a Bayesian approach.
Make no mistake, this is a very important paper. Even though the types of behaviour observed in the paper can only be considered indirect measures of intelligence, this doesn’t mean that we can’t use the data to estimate how many cetacean species are likely to be more intelligent than the bottlenose dolphin. Furthermore, if we could align the scales, as I suggested above, we could gauge how many genera are likely to be more intelligent than chimpanzees. It may even give us, for the first time ever, the potential to estimate the probability that a given species may have a greater intelligence than human. This would provide the potential to postpone any possible whaling restart, and put the burden of proving that a given whale species is not on par with humans on that industry. Tell those who have the intelligence to calculate, science can change the world.