Efficiency fosters cumulative culture across species

Recent studies in several taxa have demonstrated that animal culture can evolve to become more efficient in various contexts ranging from tool use to route learning and migration. Under recent definitions, such increases in efficiency might satisfy the core criteria of cumulative cultural evolution (CCE). However, there is not yet a satisfying consensus on the precise definition of efficiency, CCE or the link between efficiency and more complex, extended forms of CCE considered uniquely human. To bring clarity to this wider discussion of CCE, we develop the concept of efficiency by (i) reviewing recent potential evidence for CCE in animals, and (ii) clarifying a useful definition of efficiency by synthesizing perspectives found within the literature, including animal studies and the wider iterated learning literature. Finally, (iii) we discuss what factors might impinge on the informational bottleneck of social transmission, and argue that this provides pressure for learnable behaviours across species. We conclude that framing CCE in terms of efficiency casts complexity in a new light, as learnable behaviours are a requirement for the evolution of complexity. Understanding how efficiency greases the ratchet of cumulative culture provides a better appreciation of how similar cultural evolution can be between taxonomically diverse species—a case for continuity across the animal kingdom. This article is part of a discussion meeting issue ‘The emergence of collective knowledge and cumulative culture in animals, humans and machines’.

Melodic Universals Emerge or Are Sustained Through Cultural Evolution

To understand why music is structured the way it is, we need an explanation that accounts for both the universality and variability found in musical traditions. Here we test whether statistical universals that have been identified for melodic structures in music can emerge as a result of cultural adaptation to human biases through iterated learning. We use data from an experiment in which artificial whistled systems, where sounds produced with a slide whistle were learned by human participants and transmitted multiple times from person to person. These sets of whistled signals needed to be memorised and recalled and the reproductions of one participant were used as the input set for the next. We tested for the emergence of seven different melodic features, such as discrete pitches, motivic patterns, or phrase repetition, and found some evidence for the presence of most of these statistical universals. We interpret this as promising evidence that, similarly to rhythmic universals, iterated learning experiments can also unearth melodic statistical universals. More, ideally cross-cultural, experiments are nonetheless needed. Simulating the cultural transmission of artificial proto-musical systems can help unravel the origins of universal tendencies in musical structures.

Cultural evolution leads to vocal iconicity in an experimental iterated learning task

Experimental and cross-linguistic studies have shown that vocal iconicity is prevalent in words that carry meanings related to size and shape. Although these studies demonstrate the importance of vocal iconicity and reveal the cognitive biases underpinning it, there is less work demonstrating how these biases lead to the evolution of a sound symbolic lexicon in the first place. In this study, we show how words can be shaped by cognitive biases through cultural evolution. Using a simple experimental setup resembling the game telephone, we examined how a single word form changed as it was passed from one participant to the next by a process of immediate iterated learning. About 1,500 naïve participants were recruited online and divided into five condition groups. The participants in the control-group received no information about the meaning of the word they were about to hear, while the participants in the remaining four groups were informed that the word meant either big or small (with the meaning being presented in text), or round or pointy (with the meaning being presented as a picture). The first participant in a transmission chain was presented with a phonetically diverse word and asked to repeat it. Thereafter, the recording of the repeated word was played for the next participant in the same chain. The sounds of the audio recordings were then transcribed and categorized according to six binary sound parameters. By modelling the proportion of vowels or consonants for each sound parameter, the small-condition showed increases of front unrounded vowels and the pointy-condition increases of acute consonants. The results show that linguistic transmission is sufficient for vocal iconicity to emerge, which demonstrates the role non-arbitrary associations play in the evolution of language.

Lingua franca features in Italian. Evidence form an evolutionary linguistics experiment

There is no doubt about the lingua franca status of the English language (e.g. Mair 2003). It even manifested itself in an evolutionary linguistics study based on the methodology of iterated learning (cf. Kirby and Hurford 2002). In an experiment with human participants, all of whom were native speakers of Polish, aimed at producing basic yet novel linguistic systems, entrenched linguistic structures related to English could easily be found, despite the fact that the experiment’s participants were asked not to use linguistic units from existing languages (e.g. Rogalska-Chodecka 2015). When the experiment’s participants tried to notice a lexical or syntactic pattern in a set of CVCVCV strings, they referred to English words regardless of their level of language knowledge or the experimenter’s instruction. Consequently, the final product of the experiment was not a novel linguistic system, but one containing entrenched linguistic English-related structures, which proves that in the absence of known linguistic structures, referring to English ones seems to be the easiest option. The present article asks whether it is possible to “force” participants in an experiment to use certain items from the Italian lexicon (related to colour, number, and shape) instead of those that come from English, despite their declared lack of knowledge of the Italian language. The results of two studies, one with a control group where the participants were asked to learn words in English as well as random CVCVCV strings, and one “contaminated” with Italian, where random words were exchanged with Italian ones, are compared in order to determine whether Italian is as useful as English from the perspective of participants in experiments and possesses lingua franca features that can be noticed in the case of the original evolutionary experiment. It turned out that, due to its high learnability, Italian exhibits lingua franca features and, given similar historical conditions to English, could regain its historical lingua franca status.

The emergence of word-internal repetition through iterated learning: Explaining the mismatch between learning biases and language design

The idea that natural language is shaped by biases in learning plays a key role in our understanding of how human language is structured, but its corollary that there should be a correspondence between typological generalisations and ease of acquisition is not always supported. For example, natural languages tend to avoid close repetitions of consonants within a word, but developmental evidence suggests that, if anything, words containing sound repetitions are more, not less, likely to be acquired than those without. In this study, we use word-internal repetition as a test case to provide a cultural evolutionary explanation of when and how learning biases impact on language design. Two artificial language experiments showed that adult speakers possess a bias for both consonant and vowel repetitions when learning novel words, but the effects of this bias were observable in language transmission only when there was a relatively high learning pressure on the lexicon. Based on these results, we argue that whether the design of a language reflects biases in learning depends on the relative strength of pressures from learnability and communication efficiency exerted on the linguistic system during cultural transmission.

Amount of Learning and Signal Stability Modulate Emergence of Combinatorial Structure and Iconicity in Novel Signaling Systems

Iterated language learning experiments that explore emergence of linguistic structure in the laboratory vary considerably in methodological implementation, limiting generalizability of findings. Most studies also restrict themselves to exploring the emergence of combinatorial and compositional structure in isolation. Here, we use a novel signal space comprising binary auditory and visual sequences and manipulate amount of learning and temporal stability of these signals. Participants had to learn signals for meanings differing in size, shape and brightness; their productions in the test phase were transmitted to the next participant. Across transmission chains of 10 generations each, Experiment 1 varied how much learning of auditory signals took place, and Experiment 2 varied temporal stability of visual signals. We found that combinatorial structure emerged most reliably with greater amount of learning and when signals were temporally stable. Iconicity emerged with reduced amount of learning, as opportunity for rote-memorization appeared to hamper exploration of the iconic affordances of the signal space. However, emergence of combinatoriality and iconicity in these entirely unfamiliar signaling systems was too fragile to allow for compositional signal-meaning mappings to emerge, so learnability did not improve over the course of transmission. These findings underscore the importance of systematically manipulating training conditions and signal characteristics in iterated learning language learning experiments and suggest that combinatorial structure and iconicity may be a prerequisite for emergence of compositional structure in novel signaling systems.

Evolution of combinatorial structure in learned forms through embodied iterated learning in a robot collective

In this study, we use mobile robots as physical entities to model the iterated learning of collections of forms that consist of randomly generated movement sequences. The robots implement an abstract model of embodied iterated social learning in which the forms evolve due to limited perceptual abilities of the robots during multiple learning cycles. It is shown that shared chunks that consisted of similar movement sequences emerge in the learned forms, and as these emergent shared sequences can be learned with high accuracy, they cause a cumulative increase in the learnability of the collections. Therefore, we are able to present robotic experiments in which embodied learning on robots leads to combinatorial structure as a result of cultural interactions in the form of iterated learning without a communicative task.