One way to try to understand the origins of human intelligence is to look at its counterparts elsewhere in the animal kingdom. But it turns out to be more complicated than it seems. Humans have a large package of behavioral traits that are lumped together as intelligence, but many other creatures have only a limited subset of those traits. Some aspects of intelligence appear in species widely scattered across the evolutionary tree, from squids to giraffes.
Even in animals that are widely acknowledged to be intelligent, such as birds, understanding whether evolution directly shaped their intelligence or whether their intelligence emerged as a side effect of something else that evolution selected for. It can be difficult to do.
Research published today further complicates the picture. This 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 to be completely unrelated.
test everyone
The paper, written by Rockefeller University’s Jean-Nicolas Audet, Mélanie Couture, and Eric Jarvis, describes an evolutionary comparison of song learning and various intelligence tests. The authors note that humans have performed this type of analysis before, but only among members of the same species, and the results are often contradictory. The researchers suggest that this may simply be because the variation between individuals is not large enough to detect an effect.
To obtain a diverse sample, the team traveled to a protected area just north of New York City and set up nets. As long as at least a dozen males of the same species (singing males) were captured, they were included in the study. This was supplemented by some captive species. Some of them served as non-learning controls, like the black-spotted pigeon. However, songbirds such as wrens and warblers were abundant in the sample. This sample includes a variety of behaviors that can be used to classify the ability to engage in vocal learning, such as vocal learning, imitation, and expanding the song repertoire.
After starving the birds overnight, the researchers gave them a chance to complete mental tests and rewarded them with food. Four of these tests involved manipulating increasingly complex obstacles to obtain food. Another experiment tested whether birds could bypass transparent barriers to obtain food. Then, one day the two birds are given the opportunity to learn that colored objects are associated with food, and the next day they must unlearn that learning and learn a new association. Since this was not the case, we tested related learning.
With the data collected, the researchers created a score for each species based on the performance of at least a dozen individuals. They then compared those scores to information they had previously collected about their singing ability.
smart singer
The results were a little mixed. First, species classified as open-ended learners, meaning they can adopt new musical motifs throughout their lives, were significantly better at problem-solving. These include species such as cardinals, robins, and goldfinches. Among these groups, the group with the largest repertoire of songs performed best. But species that can imitate the calls of others, such as catbirds and agrackles, also scored above average. Close-ended learners, who are able to learn songs during critical years in childhood, scored near the bottom of the list.
In contrast, other intelligence tests involving self-control and associative learning did not show any particular pattern.
To test whether this effect was strong, the researchers repeated the analysis while excluding different subgroups, such as domesticated birds and non-learning birds. The association held out. Similarly, they performed a principal components analysis on all different measures of song learning complexity and showed that this was also associated with problem-solving ability. So, there seems to be a connection here as well.
Using data collected by others, the researchers also discovered that open-ended learning species have larger brains relative to their bodies. However, this relationship does not hold true for species that imitate the songs of others.
Further complicating matters, individuals of most species showed some variation in their responses to the tests. Some people’s performance decreases with distractions, such as the presence of researchers or unfamiliar objects.
it’s complicated
One message that is clear here is that intelligence is not a single thing. It is constructed from the various behavioral capacities of individuals. Therefore, we cannot expect that the evolutionary factors that promote the development of one aspect of intelligence will also apply to other aspects.
Therefore, problem-solving ability may be a fortuitous bonus due to evolutionary selection to extend singing ability. After all, singing is part of the way these species reliably produce the next generation. As we evolve, problem solving may help provide access to more food, and eventually choice may become a subject in itself. However, none of these guarantees that other aspects of intelligence will come to the fore.
All of this may help explain why surprisingly sophisticated behaviors appear to be isolated in some species. But it doesn’t do much to explain why a large suite of what we call intelligence existed in our species.
Science, 2023. DOI: 10.1126/science.adh3428 (About DOI).