For any form of communication to make it beyond the category of talking to oneself, at least two individuals must share a common lexicon. Before languages can evolve into more complex forms, there must first be a pragmatic sense in which one individual can communicate a basic idea to another. How might shared lexicons have originated? Standard explorations of language often look in well-connected social groups such as chimpanzees, frequently numbering in the tens of individuals. But we might ask if language perhaps didn’t begin in a more humble arrangement, involving social groups of just two or a few individuals, such as that found in the orangutan? Agent-based models combined with network science offer a way to study this problem. By treating nodes as agents with strict rule-based behavior and edges as opportunities for interaction, agent-based models provide frameworks for studying how behavior and connectivity interact to create emergent phenomenon, such as the evolution of cooperation and cultural change. Here we will explore an agent-based model of the naming game to address how structure influences the emergence of shared lexicons.

Words, like biological species, are born and then, someday, they die. The half-life of a word is roughly 2,000 years, meaning that in that interval about half of all words are replaced with an unrelated (noncognate) word. Where do the new words come from? There are numerous dimensions along which new words could vary from old words, so it may not be easy to see how to enter this problem. However, extending our small worlds metaphor and the observation of clusters in language, we tell a simple story that mirrors biological theories about the origin of species. Language has urban centers with well-populated and well-connected meanings (like *food* and *red*). It also has rural fringes, where words live more isolated lives as hermits with limited connections to other words (like *twang* and *ohm*). Are new words more likely to be born in urban centers or in the rural fringes?

In this final chapter, we take on an issue that perhaps precedes all the others: how and why did language evolve? Linguistic theory has recently pivoted to amass considerable research on these questions. As we’ve seen over and over in the book, simpler structures have been posited across frameworks to account for the need to explain how language evolved. However, in this book, we’ve seen many distinct approaches to understand human language. A view of language evolution that permits the pluralism of the book would be consistent with the broad approach of this work. Therefore, in this chapter, I want to turn the minimalist research agenda on its head with an alternative thesis: natural language is a complex system and its emergence is likely to have been prompted by multiple interacting factors. First, we assess the current state of the art in biolinguistics and the strong saltation claim that goes with it. Then, we challenge the assumptions that’ve resulted in the saltation picture of language evolution on evolutionary grounds. Lastly, a radical approach to language evolution in terms of complexity science is proffered based on a unique connection with systems biology.

In Chapter 14 I review all the linguistic arguments in support of the Innateness Hypothesis that we have critically examined in this book. I first summarize these arguments. We will then have a number of imaginary speakers (any resemblance to actual people in the field is purely coincidental) reflecting on the Innateness Hypothesis, and on the force of the various arguments pro and con. In this chapter I also briefly preview the arguments that are discussed in a sequel book (Genes, Brains and Evolution: The Language Debate Continued), which critically examines arguments in potential support of the Innateness Hypothesis for language that are based on other disciplines than linguistics proper. In this sequel book, we review how the nature–nurture debate has played out in a number of other sciences, such as psychology, sociology, anthropology, computational science, and a variety of biological disciplines, such as ethology and evolutionary science.

Chapter 4 shows how language has evolved through interaction. The first part focuses on the role that hand gestures, mouth movements, vocal actions, and the interplay of different modalities, together with the development of imitation capabilities, play in the evolution of language. In the second part, I show how language has evolved from interaction among people who progressively converged on the same meanings. I illustrate several new interdisciplinary approaches and methods adopted to study the emergence and evolution of language in dyads, groups, and populations, from agent-based simulations to experimental semiotics to culturomic approaches. Finally, I show how a combination of iconicity and arbitrariness might drive the cultural evolution of language. Iconic words, that is, words with a resemblance between form and meaning (e.g., "boom"), will emerge first, followed by more abstract ones, which are grounded in other words.

Chapter 3 summarizes recent and current theories of how language and conversation may have evolved and the nature of language.Chapter 3 includes discussion of animal signaling and the role of complex social organization, collaboration, imitation, and play in language evolution.It summarizes and critiques the contributions of meme theory to the social evolution account of language development, and closes with a discussion of how language extends and contributes to individual and group homeostasis.

The difference between humans and other primates has often been attributed to humans’ unique ability to learn language and more specifically, represent complex sequential and grammatical structures. Even in the case of language-trained apes, the animals are severely limited in how they put together strings of their learned symbols. This led to theories that this limitation is due to animals’ inability to represent the complex sequential and grammatical patterns needed for language. However, work testing the types of sequences and artificial grammars that nonhuman primates can represent has come a long way. Studies have shown that like humans, nonhuman primates can represent adjacent dependencies, ordinal sequences, and algebraic patterns. Until recently, the types of sequential structures attested in nonhuman animals have been limited to these linear sequences. However, recent work has shown that even in some of the most complex forms of grammatical structures, long-distance dependence and recursive sequences are within the limits of the nonhuman mind.

This chapter presents the hypothesis that working memory and language evolved in tandem. It reviews the evolutionary origins of each of the components of Baddeley’s working memory model and their role in the evolution of language. The chapter reviews the gradualist position that language did evolve slowly from aurally directed early primate calls and notes that the primary purpose of language has always been communication. The chapter also presents the novel idea that the pragmatics of speech (the purposes of speech) also evolved in tandem with the evolution of working memory. The chapter also reviews the saltationist idea that something happened to language more recent than 100,000 years ago, and that is the release of the fifth pragmatic of speech, the subjunctive mood, which expresses wishes and ideas contrary to fact. The subjunctive mood required fully modern working memory capacity, sufficient phonological storage capacity, and an enhanced visuospatial sketchpad, which are also critically involved in episodic memory recall and simulation. The phenotypic result of this genotype meant that thought experiments could be conducted in a recursive manner. We propose that the fruits of Homo sapiens’s cultural explosion, cave art, creative figurines, and highly ritualized burials, were the direct result of the wishes and imaginings that arise from subjunctive thinking and subjunctive language.

Semantic communication is about transmitting mental representations of reality. Three research questions address the nature of this process in primates. Can primates produce signals that are meaningful in a lexical sense? Are they capable of compositional semantics? Can they create and infer meaning by integrating context and intention? There is good evidence that, as recipients, primates have capacities at all three levels, whereas for signallers the evidence is less compelling. This difference may have cognitive roots, due to the fact that primate signallers are typically engaged in the here-and-now and, unlike humans, less able to refer to memory content. Future research will have to clarify what mental structures primates can take into account during communication, including entities that are not physically present.

Ontological inquiry into the nature of language has been somewhat marginal since the “linguistic turn” in philosophy (cf. Rorty, 1967), i.e. for about seventy-five years. Although the shift of emphasis from the more concrete objects of investigation to their formal properties has since been reversed, this change in zeitgeist did not give rise to a new wave of ontological rethinking. That was perhaps mainly due to the impact of social constructionism, which was just as sceptical of ontology as logical positivism, albeit from a different perspective: Rather than looking for ‘hard’ properties of true reality in formal structure, social constructionists basically aimed at deconstructing all descriptions that claimed to represent true reality. This book is a welcome sign that things may be changing.