Continuing our discussion of Kevin Laland’s Darwin’s Unfinished Symphony, on the evolution of culture, I am going to briefly cover “A tale of two fishes” (ch. 4) and “The roots of creativity” (ch. 5). Together with the chapters we have already discussed, they complete the first part of the book, devoted to the foundations of culture. (After this, we’ll move to the chapters in the second part, on the evolution of the mind.)
Chapter 4 is devoted primarily to research conducted over a period of two decades by Laland’s own lab, focusing on the contrast in the behavior between two small species of fish, the threespine and the ninespine sticklebacks. The reason for working on this sort of experimental animals is that if one is interested in social evolution then one needs to set up replicates of entire populations. Logistically, this is going to be impossible to do for large vertebrates, especially mammals, but it is eminently feasible with fish. Sticklebacks are a well studied group of 16 related species, common in rivers, streams and coastal regions of the Northern hemisphere. Evolutionarily speaking, they are closely related to seahorses.
Laland’s lab focused on sticklebacks’ use of public information, i.e., on how they socially learn from other members of their own or even of other species. When they started the research project, the consensus was that use of public information required a high degree of intelligence on the part of the animal. It turns out that was definitely not the case, thus providing another important piece of the cultural evolution puzzle. Chapter 4 details lots of fascinating experiments with these two species of sticklebacks, but I will summarize only the basic stuff, leaving it to the interested reader to dig deeper.
The basic setup is one in which an aquarium is divided into compartments. In one area some fish of either species are being fed at a high rate (“rich patch”); in a second one they are being fed at a lower rate (“poor patch”); and in a third one they can observe their fellow species members feeding before being allowed to do so themselves: “if the sticklebacks were capable of public-information use, they would be able to distinguish between the rich and the poor patch based solely on the reactions of the demonstrators to the food.” (p. 80).
Interestingly, the ninespine was apparently able to use public information and, when allowed access, swim preferentially to the rich patch. The threespine, by contrast, showed no preference, indicating that the observers in that species had not learned from the demonstrators. Why the difference?
Laland’s group performed several follow-up experiments aimed at eliminating a number of simple explanations, such as that perhaps the demonstrators of one species were not as good as the demonstrators of the other, or that there was an inter-specific difference in the visual acuity of the fish, or maybe some of the relevant cues were olfactory, not just visual. None of that was the case.
“We began to believe that what we had discovered might genuinely be an adaptive specialization in social learning, with ninespines capable of exploiting public information, while their close relatives, the threespines, were not.” (p. 81)
The answer turned out to have to do with the relative cost of social and asocial learning. The cost of asocial learning is different for the two species, because of differences in their anatomical structures. The threespine stickleback has large spines, which are very effective against predation, so much so that often the fish gets stuck into the predator’s mouth, and is forcefully rejected instead of being eaten. This is not the case with the ninespine stickleback, whose spines are more numerous but much smaller and less robust, and therefore not as effective an anti-predator device. Threespines don’t need to engage in public information use because they can afford to explore the various patches and learn on their own. That approach, by contrast, is very dangerous for the ninespines, which accordingly evolved the more advantageous habit of learning socially by observing others. Interestingly:
“The ninespines’ behavior is precisely that predicted by a sophisticated evolutionary game theory analysis conducted by an economist in order to understand human behavior.” (p. 89)
Moreover, comparative research conducted on 50 populations sampled from 8 species belonging to 5 genera showed that only the ninespine and their closest relative, the brooks sticklebacks, are capable of public information use, thus demonstrating the intricate relationship between evolutionary history, ecology, and morphology in shaping cultural evolution.
Chapter 5 of Darwin’s Unfinished Symphony opens with the classic example of animal learning and cultural spreading: the invention of a method to open home delivered milk bottles by blue tit birds back in 1921 England. The instance is well documented, and because of the involvement of amateur ornithologists, we know how quickly and how far it spread, eventually to involve several species other than the blue tits. Interestingly, the “invention” appeared to be relatively easy to come by, so that a number of animals arrived at the same solution independently, not necessarily relying on copying public information. So milk bottle opening is a good example of innovation, the devising of a solution to a new problem posed by the environment.
Things like the milk bottle opening clearly show that human beings do not have a monopoly on creativity, though Laland immediately qualifies this by remind his readers that:
“A vast difference exists between dipping food and inventing a microwave cooker, while banging cans together to send a message is a long way from developing e-mail.” (p. 100)
Still, studying innovation is crucial to understanding human creativity and cultural evolution, and it is not easy because it is difficult to recognize a behavior as innovative unless one has a solid baseline of studies on pre-innovation behaviors in whatever species of interest.
One of the classical studies on animal innovation was conducted by Edward Thorndike at Columbia University. He confined cats in small boxes from which it was difficult, but not impossible, to escape. This was something the cats clearly disliked, to put it mildly. Thorndike was able to show that cats — once they learn how to get out of the box — fine tune their behavior so that the escape becomes easier and easier. The interesting part was that the animals arrive at suitable solutions by trying out a bunch of seemingly random moves, until something happens to work, even sub-optimally. It’s innovation by trial and error, very much something human beings do quite well.
One of the most interesting things about this chapter is Laland’s detailed presentation of evidence that, as the saying goes, “necessity is the mother of invention,” meaning that innovations are triggered by new challenges faced by animals, often under unusual or novel environmental conditions. Moreover, studies in callitrichid monkeys clearly showed that it is often the older, more experienced, individuals that come up with innovative behaviors, not the young ones, who are presumably insufficiently experienced to have mastered the problems posed by their environment.
While experiments with mammals, and especially primates, are of course the most fascinating, as pointed out above, they are both logistically challenging and expensive. Hence, again, the use of fish, which are much easier to raise and manipulate in statistically sufficient numbers.
Laland then describes a series of experiments his lab has conducted on another common fish, familiar to aquarium enthusiasts: guppies. The results were fascinating:
“Innovators were significantly more likely to be females than males, more likely to be food deprived than not, and typically smaller rather than larger fish. … The observed patterns are best explained by differences among fish in their motivational state. The first individuals to solve the [problem posed by the experimenter] are those driven to find novel foraging solutions by hunger, or by the metabolic costs of growth, or pregnancy [hence the predominance of females among innovators].” (p. 112)
Research on birds yields equally tantalizing clues. For one thing, species of birds that are more capable of innovation tend to be the ones whose populations survive when introduced into a new environment. Moreover, migratory species are less likely to be innovators than non-migrant ones, apparently because they are not as capable of introducing innovations in order to cope with their environment. If you can’t thrive in a given place, then change place, seems to be the idea. So migration turns out to be an evolutionarily alternative strategy to the option of staying and coping + innovating. Finally, innovative species of birds are more likely to speciate, i.e., to give origin to new species.
Though it is difficult to carry out systematic experiments on primates, it is possible to canvass the extensive literature on primatology, searching for and categorizing examples of innovative behaviors. Laland did this with one of his collaborators, Simon Reader. They found that:
“Consistent with our hypothesis that necessity was the mother of much animal innovation (derived from our fish experiments), across all primates [we] found more reported incidences of innovation in low-status individuals and fewer reports of innovation in high-status individuals than expected in either, given their numbers in the populations. … [We] found that approximately half of the instances of innovation that had taken place among primates had followed some sort of ecological challenge, such as a period of food shortage, a dry season, or habitat degradation.” (pp. 116-117)
And here is the kicker: controlling for phylogenetic relatedness, there is a very strong correlation between a tendency of a species to innovate and both its relative and absolute brain size. This, however, led to a puzzle: while the obvious conclusion to be drawn is that intelligence (measured by brain size as a proxy) has been favored in certain lineages in order to facilitate social learning and innovation, it is also true that several small-brained species — from fruit flies to fish — are capable of both. Why, then, evolve large brains to begin with? That’s going to be the next topic, in the second part of the book.