One way we try to understand the origins of human intelligence is to look at its equivalents elsewhere in the animal world. But this seems to be more complicated than it may seem. Humans have a large set of behavioral traits that we lump together as intelligence, while many other creatures only have a limited subset of those traits. Some aspects of intelligence appear in species spread widely across the evolutionary tree, from squid to giraffes.
Even in animals with widely recognized intellectual abilities such as birds, it can be difficult to understand whether evolution directly shaped their intelligence or whether their intelligence emerged as a side effect of something else that evolution co-opted.
A study released today complicates the picture a little more. It convincingly shows that the ability to learn complex new songs is associated with problem solving in a wide range of bird species. But it also shows that other things we associate with intelligence, such as associative learning, seem completely unrelated.
The paper, written by Jean-Nicolas Audet, Mélanie Couture, and Eric Jarvis of The Rockefeller University, describes an evolutionary comparison between song learning and a variety of intelligence tests. The authors note that humans have performed this type of analysis before, but only between individuals of the same species, and the results have often been contradictory. The team suggests that it is possible that this is simply because the variation between individuals is not large enough to detect an effect.
To get a diverse sample, the team went to a reserve north of New York City and set up nets. As long as they captured at least twelve males of a species (those that perform the singing), they were included in the study. This was supplemented by a couple of captive species. Some of these creatures, such as the mourning dove, served as nonteaching controls. But the sample was crowded with songbirds such as wrens and warblers. Among this sample, there are a variety of behaviors, such as vocal learning, imitation, and extended song repertoire that can be used to classify their ability to engage in vocal learning.
After letting the birds starve overnight, the team gave them a chance to complete mental tests in which they were given food as a reward. Four of these tests involved manipulating obstacles of increasing complexity to reach food. Another test tested whether birds were able to navigate around a transparent barrier to obtain food. Two tested associated learning, where birds were given the opportunity to learn that a colorful object was associated with food one day, and then had to unlearn that and learn a new association the next day.
By collecting this data, the researchers created scores for each type based on the performance of at least a dozen individuals. They then compared those results with previously collected information about their singing abilities.
The results were a bit complicated. For starters, species classified as open-ended learners — meaning they can incorporate elements of a new song throughout their lives — were much better at solving problems. These include species such as cardinals, robins, and goldfinches. Within this group, those with the largest repertoire of songs performed the best. But species that can imitate the calls of others, such as the catbird and the grackle, also scored above average. Closed-ended learners, who can learn songs during a critical period when they are young, scored near the bottom of the list.
In contrast, there was no specific pattern in the other intelligence tests, which included self-control and associative learning.
To test whether this effect was robust, the researchers repeated the analysis excluding different subgroups, such as domesticated or uneducated birds. The association held out. Likewise, they analyzed principal components of all different measures of song learning complexity, and showed that this also correlates with problem-solving abilities. So, there seems to be a connection here.
Using data collected by others, the researchers also found that open-ended learning species have larger brains relative to their bodies. But this relationship does not hold in genres that imitate other people’s songs.
To complicate matters further, individuals of most species showed some variation in how they responded to the tests. Distractions, such as the presence of a researcher or an unfamiliar object, caused some individuals to perform poorly.
One clear message here is that intelligence is not one thing; It is built from a great variety of individual behavioral abilities. For this reason, we cannot expect that the evolutionary factors driving the development of one aspect of intelligence apply to any of the others.
So, it’s possible that problem solving is an incidental bonus from evolutionary selection for expanded song abilities—singing, after all, is part of how these species ensure they produce the next generation. Once evolved, problem solving can help provide access to more food, and thus can end up being the subject of choice itself. But none of this guarantees that any other aspect of intelligence will come to the fore.
All of this could help explain why some evolved behaviors are surprisingly isolated in some species. But it doesn’t go far in explaining why there is such a wide range of things we call intelligence in our species.
Science, 2023. DOI: 10.1126/science.adh3428 (About digital IDs).
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