On the antiquity of language: the reinterpretation of Neandertal linguistic capacities and its consequences

Why did humans surpass all other primates? Are our brains so different? Part 1

This review is based on a conference presented in June 2023. Its main objective is to explain the cognitive differences between humans and non-human primates (NHPs) focusing on characteristics of their brains. It is based on the opinion of a clinical neurologist and does not intend to go beyond an overview of this complex topic. As language is the main characteristic differentiating humans from NHPs, this review is targeted at their brain networks related to language. NHPs have rudimentary forms of language, including primitive lexical/semantic signs. Humans have a much broader lexical/semantic repertory, but syntax is the most important characteristic, which is probably unique to Homo sapiens. Angular gyrus, Broca's area, temporopolar areas, and arcuate fascicle, are much more developed in humans. These differences may explain why NHPs did not develop a similar language to ours. Language had a profound influence on all other higher nervous activities.

Opposite size illusions for inverted faces and letters

Words are the primary means by which we communicate meaning and ideas, while faces provide important social cues. Studying visual illusions involving faces and words can elucidate the hierarchical processing of information as different regions of the brain are specialised for face recognition and word processing. A size illusion has previously been demonstrated for faces, whereby an inverted face is perceived as larger than the same stimulus upright. Here, two experiments replicate the face size illusion, and investigate whether the illusion is also present for individual letters (Experiment 1), and visual words and pseudowords (Experiment 2). Results confirm a robust size Illusion for faces. Letters, words and pseudowords and unfamiliar letters all show a reverse size illusion, as we previously demonstrated for human bodies. Overall, results indicate the illusion occurs in early perceptual stages upstream of semantic processing. Results are consistent with the idea of a general-purpose mechanism that encodes curvilinear shapes found in both scripts and our environment. Word and face perception rely on specialised, independent cognitive processes. The underestimation of the size of upright stimuli is specific to faces. Opposite size illusions may reflect differences in how size information is encoded and represented in stimulus-specialised neural networks, resulting in contrasting perceptual effects. Though words and faces differ visually, there is both symmetry and asymmetry in how the brain 'reads' them.

Open Problems in Computational Historical Linguistics

Problems constitute the starting point of all scientific research. The essay reflects on the different kinds of problems that scientists address in their research and discusses a list of 10 problems for the field of computational historical linguistics, that was proposed throughout 2019 in a series of blog posts. In contrast to problems identified in different contexts, these problems were considered to be solvable, but no solution could be proposed back then. By discussing the problems in the light of developments that have been made in the field during the past five years, a modified list is proposed that takes new insights into account but also finds that the majority of the problems has not yet been solved.

The gradual coevolution of syntactic combinatorics and categorization under the effects of human self-domestication: a proposal

The gradual emergence of syntax has been claimed to be engaged in a feedback loop with Human Self-Domestication (HSD), both processes resulting from, and contributing to, enhanced connectivity in selected cortico-striatal networks, which is the mechanism for attenuating reactive aggression, the hallmark of HSD, but also the mechanism of cross-modality, relevant for syntax. Here, we aim to bridge the gap between these brain changes and further changes facilitated by the gradual complexification of grammars. We propose that increased cross-modality would have enabled and supported, more specifically, a feedback loop between categorization abilities relevant for vocabulary building and the gradual emergence of syntactic structure, including Merge. In brief, an enhanced categorization ability not only brings about more distinct categories, but also a critical number of tokens in each category necessary for Merge to take off in a systematic and productive fashion; in turn, the benefits of expressive capabilities brought about by productive Merge encourage more items to be categorized, and more categories to be formed, thus further potentiating categorization abilities, and with it, syntax again. We support our hypothesis with evidence from the domains of language development and animal communication, but also from biology, neuroscience, paleoanthropology, and clinical linguistics.

The relevance of the unique anatomy of the human prefrontal operculum to the emergence of speech

Identifying the evolutionary origins of human speech remains a topic of intense scientific interest. Here we describe a unique feature of adult human neuroanatomy compared to chimpanzees and other primates that may provide an explanation of changes that occurred to enable the capacity for speech. That feature is the Prefrontal extent of the Frontal Operculum (PFOp) region, which is located in the ventrolateral prefrontal cortex, adjacent and ventromedial to the classical Broca's area. We also show that, in chimpanzees, individuals with the most human-like PFOp, particularly in the left hemisphere, have greater oro-facial and vocal motor control abilities. This critical discovery, when combined with recent paleontological evidence, suggests that the PFOp is a recently evolved feature of human cortical structure (perhaps limited to the genus Homo) that emerged in response to increasing selection for cognitive and motor functions evident in modern speech abilities.

Evolution of the human tongue and emergence of speech biomechanics

The tongue is one of the organs most central to human speech. Here, the evolution and species-unique properties of the human tongue is traced, via reference to the apparent articulatory behavior of extant non-human great apes, and fossil findings from early hominids - from a point of view of articulatory phonetics, the science of human speech production. Increased lingual flexibility provided the possibility of mapping of articulatory targets, possibly via exaptation of manual-gestural mapping capacities evident in extant great apes. The emergence of the human-specific tongue, its properties, and morphology were crucial to the evolution of human articulate speech.

What made us "hunter-gatherers of words"

This paper makes three interconnected claims: (i) the "human condition" cannot be captured by evolutionary narratives that reduce it to a recent 'cognitive modernity', nor by narratives that eliminates all cognitive differences between us and out closest extinct relatives, (ii) signals from paleogenomics, especially coming from deserts of introgression but also from signatures of positive selection, point to the importance of mutations that impact neurodevelopment, plausibly leading to temperamental differences, which may impact cultural evolutionary trajectories in specific ways, and (iii) these trajectories are expected to affect the language phenotypes, modifying what is being learned and how it is put to use. In particular, I hypothesize that these different trajectories influence the development of symbolic systems, the flexible ways in which symbols combine, and the size and configurations of the communities in which these systems are put to use.

Laughter and its role in the evolution of human social bonding

In anthropoid primates, social grooming is the principal mechanism (mediated by the central nervous system endorphin system) that underpins social bonding. However, the time available for social grooming is limited, and this imposes an upper limit on the size of group that can be bonded in this way. I suggest that, when hominins needed to increase the size of their groups beyond the limit that could be bonded by grooming, they co-opted laughter (a modified version of the play vocalization found widely among the catarrhine primates) as a form of chorusing to fill the gap. I show, first, that human laughter both upregulates the brain's endorphin system and increases the sense of bonding between those who laugh together. I then use a reverse engineering approach to model group sizes and grooming time requirements for fossil hominin species to search for pinch points where a phase shift in bonding mechanisms might have occurred. The results suggest that the most likely time for the origin of human-like laughter is the appearance of the genus Homoca 2.5 Ma.

This article is part of the theme issue ‘Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience’.

Language evolution is not limited to speech acquisition: a large study of language development in children with language deficits highlights the importance of the voluntary imagination component of language

Did the boy bite the cat or was it the other way around? When processing a sentence with several objects, one has to establish ‘who did what to whom’. When a sentence cannot be interpreted by recalling an image from memory, we rely on the special type of voluntary constructive imagination called Prefrontal synthesis (PFS). PFS is defined as the ability to juxtapose mental visuospatial objects at will. We hypothesised that PFS has fundamental importance for language acquisition. To test this hypothesis, we designed a PFS-targeting intervention and administered it to 6,454 children with language deficiencies (age 2 to 12 years). The results from the three-year-long study demonstrated that children who engaged with the PFS intervention showed 2.2-fold improvement in combinatorial language comprehension compared to children with similar initial evaluations. These findings suggest that language can be improved by training the PFS and exposes the importance of the visuospatial component of language. This manuscript reflects on the experimental findings from the point of view of human language evolution. When used as a proxy for evolutionary language acquisition, the study results suggest a dichotomy of language evolution, with its speech component and its visuospatial component developing in parallel. The study highlights the radical idea that evolutionary acquisition of language was driven primarily by improvements of voluntary imagination rather than by improvements in the speech apparatus.

Gesture is the primary modality for language creation

How language began is one of the oldest questions in science, but theories remain speculative due to a lack of direct evidence. Here, we report two experiments that generate empirical evidence to inform gesture-first and vocal-first theories of language origin; in each, we tested modern humans' ability to communicate a range of meanings (995 distinct words) using either gesture or non-linguistic vocalization. Experiment 1 is a cross-cultural study, with signal Producers sampled from Australia (n = 30, M_age = 32.63, s.d. = 12.42) and Vanuatu (n = 30, M_age = 32.40, s.d. = 11.76). Experiment 2 is a cross-experiential study in which Producers were either sighted (n = 10, M_age = 39.60, s.d. = 11.18) or severely vision-impaired (n = 10, M_age = 39.40, s.d. = 10.37). A group of undergraduate student Interpreters guessed the meaning of the signals created by the Producers (n = 140). Communication success was substantially higher in the gesture modality than the vocal modality (twice as high overall; 61.17% versus 29.04% success). This was true within cultures, across cultures and even for the signals produced by severely vision-impaired participants. The success of gesture is attributed in part to its greater universality (i.e. similarity in form across different Producers). Our results support the hypothesis that gesture is the primary modality for language creation.

Language, Childhood, and Fire: How We Learned to Love Sharing Stories

Stories do not fossilize. Thus, exploring tales shared during prehistory, the longest part of human history inevitably becomes speculative. Nevertheless, various attempts have been made to find a more scientifically valid way into our deep human past of storytelling. Following the social brain hypothesis, we suggest including into the theory of human storytelling more fine-grained and evidence-based findings (from archaeology, the cognitive sciences, and evolutionary psychology) about the manifold exaptation and adaptation, genetic changes, and phenotypic plasticity in the deep human past, which all shaped the emergence of storytelling in hominins. We identify three preconditions for humans sharing stories: first, the long evolution of language in the different taxa as one of the preconditions of ostensive signaling; second, the pivotal role of childhood in the evolution of collaborative intentionality; and third, the role of fireside chats in the rise of elaborative (i.e., narrative) sharing of stories. We propose that humans, albeit perhaps no other hominins learned to understand others through sharing stories, not only as intentional agents, but also as mental ones.

Overlooked evidence for semantic compositionality and signal reduction in wild chimpanzees (Pan troglodytes)

Recent discoveries of semantic compositionality in Japanese tits have enlivened the discussions on the presence of this phenomenon in wild animal communication. Data on semantic compositionality in wild apes are lacking, even though language experiments with captive apes have demonstrated they are capable of semantic compositionality. In this paper, I revisit the study by Boesch (Hum. Evol. 6:81–89, 1991) who investigated drumming sequences by an alpha male in a chimpanzee (Pan troglodytes) community in the Taï National Park, Côte d’Ivoire. A reanalysis of the data reveals that the alpha male produced semantically compositional combined messages of travel direction change and resting period initiation. Unlike the Japanese tits, the elements of the compositional expression were not simply juxtaposed but displayed structural reduction, while one of the two elements in the expression coded the meanings of both elements. These processes show relative resemblance to blending and fusion in human languages. Also unlike the tits, the elements of the compositional expression did not have a fixed order, although there was a fixed distribution of drumming events across the trees used for drumming. Because the elements of the expression appear to carry verb-like meanings, the compositional expression also resembles simple verb-verb constructions and short paratactic combinations of two clauses found across languages. In conclusion, the reanalysis suggests that semantic compositionality and phenomena resembling paratactic combinations of two clauses might have been present in the communication of the last common ancestor of chimpanzees and humans, not necessarily in the vocal modality.

DLX5/6 GABAergic Expression Affects Social Vocalization: Implications for Human Evolution

DLX5 and DLX6 are two closely related transcription factors involved in brain development and in GABAergic differentiation. The DLX5/6 locus is regulated by FoxP2, a gene involved in language evolution and has been associated with neurodevelopmental disorders and mental retardation. Targeted inactivation of Dlx5/6 in mouse GABAergic neurons (Dlx5/6VgatCre mice) results in behavioral and metabolic phenotypes notably increasing lifespan by 33%. Here, we show that Dlx5/6VgatCre mice present a hyper-vocalization and hyper-socialization phenotype. While only 7% of control mice emitted more than 700 vocalizations/10 min, 30% and 56% of heterozygous or homozygous Dlx5/6VgatCre mice emitted more than 700 and up to 1,400 calls/10 min with a higher proportion of complex and modulated calls. Hyper-vocalizing animals were more sociable: the time spent in dynamic interactions with an unknown visitor was more than doubled compared to low-vocalizing individuals. The characters affected by Dlx5/6 in the mouse (sociability, vocalization, skull, and brain shape…) overlap those affected in the "domestication syndrome". We therefore explored the possibility that DLX5/6 played a role in human evolution and "self-domestication" comparing DLX5/6 genomic regions from Neanderthal and modern humans. We identified an introgressed Neanderthal haplotype (DLX5/6-N-Haplotype) present in 12.6% of European individuals that covers DLX5/6 coding and regulatory sequences. The DLX5/6-N-Haplotype includes the binding site for GTF2I, a gene associated with Williams-Beuren syndrome, a hyper-sociability and hyper-vocalization neurodevelopmental disorder. The DLX5/6-N-Haplotype is significantly underrepresented in semi-supercentenarians (>105 years of age), a well-established human model of healthy aging and longevity, suggesting their involvement in the coevolution of longevity, sociability, and speech.

The vocal tract as a time machine: inferences about past speech and language from the anatomy of the speech organs

While speech and language do not fossilize, they still leave traces that can be extracted and interpreted. Here, we suggest that the shape of the hard structures of the vocal tract may also allow inferences about the speech of long-gone humans. These build on recent experimental and modelling studies, showing that there is extensive variation between individuals in the precise shape of the vocal tract, and that this variation affects speech and language. In particular, we show that detailed anatomical information concerning two components of the vocal tract (the lower jaw and the hard palate) can be extracted and digitized from the osteological remains of three historical populations from The Netherlands, and can be used to conduct three-dimensional biomechanical simulations of vowel production. We could recover the signatures of inter-individual variation between these vowels, in acoustics and articulation. While 'proof-of-concept', this study suggests that older and less well-preserved remains could be used to draw inferences about historic and prehistoric languages. Moreover, it forces us to clarify the meaning and use of the uniformitarian principle in linguistics, and to consider the wider context of language use, including the anatomy, physiology and cognition of the speakers. This article is part of the theme issue 'Reconstructing prehistoric languages'.

The sounds of prehistoric speech

Evidence is reviewed for widespread phonological and phonetic tendencies in contemporary languages. The evidence is based largely on the frequency of sound types in word lists and in phoneme inventories across the world's languages. The data reviewed point to likely tendencies in the languages of the Upper Palaeolithic. These tendencies include the reliance on specific nasal and voiceless stop consonants, the relative dispreference for posterior voiced consonants and the use of peripheral vowels. More tenuous hypotheses related to prehistoric languages are also reviewed. These include the propositions that such languages lacked labiodental consonants and relied more heavily on vowels, when contrasted to many contemporary languages. Such hypotheses suggest speech has adapted to subtle pressures that may in some cases vary across populations. This article is part of the theme issue 'Reconstructing prehistoric languages'.

Capturing the Effects of Domestication on Vocal Learning Complexity

Domesticated and vocal learning species can serve as informative model organisms for the reduction of reactive aggression and emergence of speech in our lineage. Amidst mounting evidence that domestication modifies vocal repertoires across different species, we focus on the domesticated Bengalese finch, which has a more complex song than the wild-type white-rumped munia. Our explanation for this effect revolves around the glutamate neurotransmitter system. Glutamate signaling (i) is implicated in birdsong learning, (ii) controls dopamine activity in neural circuits crucial for vocal learning, (iii) is disproportionately targeted in the evolution of domesticates, and (iv) regulates stress responses and aggressive behaviors attenuated under domestication. We propose that attenuated excitation of stress-related neural circuits potentiates vocal learning via altered dopaminergic signaling.

Understanding Human Cognitive Uniqueness

Humanity has regarded itself as intellectually superior to other species for millennia, yet human cognitive uniqueness remains poorly understood. Here, we evaluate candidate traits plausibly underlying our distinctive cognition (including mental time travel, tool use, problem solving, social cognition, and communication) as well as domain generality, and we consider how human cognitive uniqueness may have evolved. We conclude that there are no traits present in humans and absent in other animals that in isolation explain our species' superior cognitive performance; rather, there are many cognitive domains in which humans possess unusually potent capabilities compared to those found in other species. Humans are flexible cognitive all-rounders, whose proficiency arises through interactions and reinforcement between cognitive domains at multiple scales.

Triangulating Neanderthal cognition: A tale of not seeing the forest for the trees

The inference of Neanderthal cognition, including their cultural and linguistic capabilities, has persisted as a fiercely debated research topic for decades. This lack of consensus is substantially based on inherent uncertainties in reconstructing prehistory out of indirect evidence as well as other methodological limitations. Further factors include systemic difficulties within interdisciplinary discourse, data artifacts, historic research biases, and the sheer scope of the relevant research. Given the degrees of freedom in interpretation ensuing from these complications, any attempt to find approximate answers to the yet unsettled pertinent discourse may not rest on single studies, but instead a careful and comprehensive interdisciplinary synthesis of findings. Triangulating Neanderthals' cognition by considering the plethora of data, diverse perspectives and aforementioned complexities present within the literature constitutes the currently most reliable pathway to tentative conclusions. While some uncertainties remain, such an approach paints the picture of an extensive shared humanity between anatomically modern humans and Neanderthals. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Linguistics > Evolution of Language.

Humanity and the left hemisphere: The story of half a brain

Until fairly late in the nineteenth century, it was held that the brain was bilaterally symmetrical. With the discovery of left-brain dominance for language, the so-called "laws of symmetry" were revoked, and asymmetry was then seen as critical to the human condition, with the left hemisphere, in particular, assuming superordinate properties. I trace this idea from the early discoveries of the late nineteenth century through the split-brain studies of the 1960s, and beyond. Although the idea has persisted, the evidence has revealed widespread cerebral asymmetries in nonhuman animals, and even language and its asymmetries are increasingly understood to have evolved gradually, rather than in a single speciation event. The left hemisphere nevertheless seemed to take over a role previously taken by other structures, such as the pineal gland and the hippocampus minor, in a determined effort to place humans on a pedestal above all other species.

Future Directions in Peer Relations Research

Peer relationships among youth have been examined as predictors of mental health outcomes for at least fifty years, revealing dozens of discrete peer constructs that each are associated with adjustment in childhood, adolescence, and later in adulthood. Future research may benefit by examining a range of new outcomes and psychological processes that have been discussed recently in related literatures. This paper reviews recent research on interpersonal determinants of physical health outcomes, and opportunities for greater examination of 1) peer influence processes toward health risk behaviors; 2) neural correlates of peer adversity; 3) adverse peer experiences that may affect physiological markers of stress response; and 4) immune system markers of peer adversity. Additional future directions include the study of differences in the forms and functions of peer interactions within the digital age.

Crossing the Rubicon: Behaviorism, Language, and Evolutionary Continuity

Euan Macphail's work and ideas captured a pivotal time in the late 20th century when behavioral laws were considered to apply equally across vertebrates, implying equal intelligence, but it was also a time when behaviorism was challenged by the view that language was unique to humans, and bestowed a superior mental status. Subsequent work suggests greater continuity between humans and their forebears, challenging the Chomskyan assumption that language evolved in a single step ("the great leap forward") in humans. Language is now understood to be based on an amalgam of cognitive functions, including mental time travel, theory of mind, and what may be more broadly defined as imagination. These functions probably evolved gradually in hominin evolution and are present in varying degrees in non-human species. The blending of language into cognition provides for both interspecies differences in mental function, and continuity between humans and other species. What does seem to be special to humans is the ability to communicate the contents of imagination, although even this is not absolute, and is perhaps less adaptive than we like to think.

Human Social Evolution: Self-Domestication or Self-Control?

The self-domestication hypothesis suggests that, like mammalian domesticates, humans have gone through a process of selection against aggression - a process that in the case of humans was self-induced. Here, we extend previous proposals and suggest that what underlies human social evolution is selection for socially mediated emotional control and plasticity. In the first part of the paper we highlight general features of human social evolution, which, we argue, is more similar to that of other social mammals than to that of mammalian domesticates and is therefore incompatible with the notion of human self-domestication. In the second part, we discuss the unique aspects of human evolution and propose that emotional control and social motivation in humans evolved during two major, partially overlapping stages. The first stage, which followed the emergence of mimetic communication, the beginnings of musical engagement, and mimesis-related cognition, required socially mediated emotional plasticity and was accompanied by new social emotions. The second stage followed the emergence of language, when individuals began to instruct the imagination of their interlocutors, and to rely even more extensively on emotional plasticity and culturally learned emotional control. This account further illustrates the significant differences between humans and domesticates, thus challenging the notion of human self-domestication.

Evolutionary Dynamics Do Not Motivate a Single-Mutant Theory of Human Language

One of the most controversial hypotheses in cognitive science is the Chomskyan evolutionary conjecture that language arose instantaneously in humans through a single mutation. Here we analyze the evolutionary dynamics implied by this hypothesis, which has never been formalized before. The hypothesis supposes the emergence and fixation of a single mutant (capable of the syntactic operation Merge) during a narrow historical window as a result of frequency-independent selection under a huge fitness advantage in a population of an effective size no larger than ~15 000 individuals. We examine this proposal by combining diffusion analysis and extreme value theory to derive a probabilistic formulation of its dynamics. We find that although a macro-mutation is much more likely to go to fixation if it occurs, it is much more unlikely a priori than multiple mutations with smaller fitness effects. The most likely scenario is therefore one where a medium number of mutations with medium fitness effects accumulate. This precise analysis of the probability of mutations occurring and going to fixation has not been done previously in the context of the evolution of language. Our results cast doubt on any suggestion that evolutionary reasoning provides an independent rationale for a single-mutant theory of language.

From Physical Aggression to Verbal Behavior: Language Evolution and Self-Domestication Feedback Loop

We propose that human self-domestication favored the emergence of a less aggressive phenotype in our species, more precisely phenotype prone to replace (reactive) physical aggression with verbal aggression. In turn, the (gradual) transition to verbal aggression and to more sophisticated forms of verbal behavior favored self-domestication, with the two processes engaged in a mutually reinforcing feedback loop, considering that verbal behavior entails not only less violence and better survival but also more opportunities to interact longer and socialize with more conspecifics, ultimately enabling the emergence of more complex forms of language. Whereas in the case of self-domestication, sexual selection has been proposed to work against physical aggression traits, in the case of verbal insult, the selection has been proposed to work in favor of verbal aggression. The tension between these two seemingly opposing forces gets resolved/alleviated by a tendency to replace physical aggression with verbal aggression and with verbal behavior more generally. This also helps solve the paradox of the Self-Domestication Hypothesis regarding aggression, more precisely why aggression in humans has been reduced only when it comes to reactive aggression, but not when it comes to proactive aggression, the latter exhibiting an increase in the advent of modern language. We postulate that this feedback loop was particularly important during the time period arguably between 200 and 50 kya, when humans were not fully modern, neither in terms of their skull/brain morphology and their behavior/culture nor in terms of their self-domestication. The novelty of our approach lies in (1) giving an active role to early forms of language in interacting with self-domestication processes; (2) providing specific linguistic details and functions of this early stage of grammar (including insult and humor); (3) supplying neurobiological, ontogenetic, and clinical evidence of a link between (reactive) aggression and (reactive) verbal behavior; (4) identifying proxies of the earlier stages in evolution among cognitive disorders; and (5) identifying specific points of contact and mutual reinforcement between these two processes (self-domestication and early language evolution), including reduction in physical aggression and stress/tension, as well as sexual selection.

Constructing a Consensus on Language Evolution? Convergences and Differences Between Biolinguistic and Usage-Based Approaches

Two of the main theoretical approaches to the evolution of language are biolinguistics and usage-based approaches. Both are often conceptualized as belonging to seemingly irreconcilable “camps.” Biolinguistic approaches assume that the ability to acquire language is based on a language-specific genetic foundation. Usage-based approaches, on the other hand, stress the importance of domain-general cognitive capacities, social cognition, and interaction. However, there have been a number of recent developments in both paradigms which suggest that biolinguistic and usage-based approaches are actually moving closer together. For example, theoretical advancements such as evo-devo and complex adaptive system theory have gained traction in the language sciences, leading to changed conceptions of issues like the relative influence of “nature” and “nurture.” In this paper, we outline points of convergence between current minimalist biolinguistic and usage-based approaches regarding four contentious issues: (1) modularity and domain specificity; (2) innateness and development; (3) cultural and biological evolution; and (4) knowledge of language and its description. We show that across both paradigms, researchers have come to increasingly embrace more complex views of these issues. They also have come to appreciate the view that biological and cultural evolution are closely intertwined, which lead to an increased amount of common ground between minimalist biolinguistics and usage-based approaches.

Hypotheses for the Evolution of Reduced Reactive Aggression in the Context of Human Self-Domestication

Parallels in anatomy between humans and domesticated mammals suggest that for the last 300,000 years, Homo sapiens has experienced more intense selection against the propensity for reactive aggression than other species of Homo. Selection against reactive aggression, a process that can also be called self-domestication, would help explain various physiological, behavioral, and cognitive features of humans, including the unique system of egalitarian male hierarchy in mobile hunter-gatherers. Here I review nine leading proposals for the occurrence of self-domestication in H. sapiens. To account for the domestication syndrome, proposals must explain what led to a decline in fitness of highly aggressive males, and why the explanatory factor applies only to H. sapiens and not to other species of Homo. The proposed explanations invoke genetic group selection; group-structured culture selection (also known as cultural group selection); social selection by female mate choice; social selection by male partner choice; increased self-control; cooperative breeding; high population density; use of lethal weapons; and language-based conspiracy. Most of these proposals face difficulties in accounting for the origins and/or maintenance of reduced reactive aggression. I conclude that the evolution of language-based conspiracy, which is a form of collective intentionality, was the key factor initiating and maintaining self-domestication in H. sapiens, because it is the most convincing mechanism for explaining the selective pressure against individually powerful fighters. Sophisticated language enabled males of low fighting prowess to cooperatively plan the execution of physically aggressive and domineering alpha males. This system is known today as a leveling mechanism in small-scale societies. Group-structured culture selection possibly accelerated the process.

Language evolution to revolution: the leap from rich-vocabulary non-recursive communication system to recursive language 70,000 years ago was associated with acquisition of a novel component of imagination, called Prefrontal Synthesis, enabled by a mutation that slowed down the prefrontal cortex maturation simultaneously in two or more children – the Romulus and Remus hypothesis

There is an overwhelming archeological and genetic evidence that modern speech apparatus was acquired by hominins by 600,000 years ago. On the other hand, artifacts signifying modern imagination, such as (1) composite figurative arts, (2) bone needles with an eye, (3) construction of dwellings, and (4) elaborate burials arose not earlier than 70,000 years ago. It remains unclear (1) why there was a long gap between acquisition of modern speech apparatus and modern imagination, (2) what triggered the acquisition of modern imagination 70,000 years ago, and (3) what role language might have played in this process. Our research into evolutionary origin of modern imagination has been driven by the observation of a temporal limit for the development of a particular component of imagination. Modern children not exposed to recursive language in early childhood never acquire the type of active constructive imagination called Prefrontal Synthesis (PFS). Unlike vocabulary and grammar acquisition, which can be learned throughout one’s lifetime, there is a strong critical period for the development of PFS and individuals not exposed to recursive language in early childhood can never acquire PFS as adults. Their language will always lack understanding of spatial prepositions and recursion that depend on the PFS ability. In a similar manner, early hominins would not have been able to learn recursive language as adults and, therefore, would not be able to teach recursive language to their children. Thus, the existence of a strong critical period for PFS acquisition creates an evolutionary barrier for behavioral modernity. An evolutionary mathematical model suggests that a synergistic confluence of three events (1) a genetic mutation that extended the critical period by slowing down the prefrontal cortex development simultaneously in two or more children, (2) invention of recursive elements of language, such as spatial prepositions, by these children and (3) their dialogic communications using these recursive elements, resulted in concurrent conversion of a non-recursive communication system of their parents to recursive language and acquisition of PFS around 70,000 years ago.

Language, Memory, and Mental Time Travel: An Evolutionary Perspective

Language could not exist without memory, in all its forms: working memory for sequential production and understanding, implicit memory for grammatical rules, semantic memory for knowledge, and episodic memory for communicating personal experience. Episodic memory is part of a more general capacity for mental travel both forward and backward in time, and extending even into fantasy and stories. I argue that the generativity of mental time travel underlies the generativity of language itself, and could be the basis of what Chomsky calls I-language, or universal grammar (UG), a capacity for recursive thought independent of communicative language itself. Whereas Chomsky proposed that I-language evolved in a single step well after the emergence of Homo sapiens, I suggest that generative imagination, extended in space and time, has a long evolutionary history, and that it was the capacity to share internal thoughts, rather than the nature of the thoughts themselves, that more clearly distinguishes humans from other species.

Multimodal communication and language origins: integrating gestures and vocalizations

The presence of divergent and independent research traditions in the gestural and vocal domains of primate communication has resulted in major discrepancies in the definition and operationalization of cognitive concepts. However, in recent years, accumulating evidence from behavioural and neurobiological research has shown that both human and non-human primate communication is inherently multimodal. It is therefore timely to integrate the study of gestural and vocal communication. Herein, we review evidence demonstrating that there is no clear difference between primate gestures and vocalizations in the extent to which they show evidence for the presence of key language properties: intentionality, reference, iconicity and turn-taking. We also find high overlap in the neurobiological mechanisms producing primate gestures and vocalizations, as well as in ontogenetic flexibility. These findings confirm that human language had multimodal origins. Nonetheless, we note that in great apes, gestures seem to fulfil a carrying (i.e. predominantly informative) role in close-range communication, whereas the opposite holds for face-to-face interactions of humans. This suggests an evolutionary shift in the carrying role from the gestural to the vocal stream, and we explore this transition in the carrying modality. Finally, we suggest that future studies should focus on the links between complex communication, sociality and cooperative tendency to strengthen the study of language origins.

A catalog of single nucleotide changes distinguishing modern humans from archaic hominins

Throughout the past decade, studying ancient genomes has provided unique insights into human prehistory, and differences between modern humans and other branches like Neanderthals can enrich our understanding of the molecular basis of unique modern human traits. Modern human variation and the interactions between different hominin lineages are now well studied, making it reasonable to go beyond fixed genetic changes and explore changes that are observed at high frequency in present-day humans. Here, we identify 571 genes with non-synonymous changes at high frequency. We suggest that molecular mechanisms in cell division and networks affecting cellular features of neurons were prominently modified by these changes. Complex phenotypes in brain growth trajectory and cognitive traits are likely influenced by these networks and other non-coding changes presented here. We propose that at least some of these changes contributed to uniquely human traits, and should be prioritized for experimental validation.

Infinite Generation of Language Unreachable From a Stepwise Approach

Language is commonly thought of as a culturally evolved system of communication rather than a computational system for generating linguistic objects that express thought. Furthermore, language is commonly argued to have gradually evolved from finite proto-language which eventually developed into infinite language of modern humans. Both ideas are typically integrated in accounts that attempt to explain gradual evolution of more complex language from the increasingly strong pressures of communicative needs. Recently some arguments have been presented that the probability of the emergence of infinitely productive languages is increased by communicative pressures. These arguments fail. The question whether decidable languages evolve into infinite language is vacuous since infinite generation is the null hypothesis for a generative procedure. The argument that increasing cardinality leads to infinite language is incoherent since it essentially conflates concepts of performance with notions of competence. Recursive characterization of infinite language is perfectly consistent with finite output. Further, the discussion completely ignores a basic insight that language is not about decidability of weakly generated strings but rather about properties of strongly generated structures. Finally, the plausibility proof that infinite productivity evolves from finite language is false because it confuses (infinite) cardinal numbers with (natural) ordinal numbers. Infinite generation cannot be reached with a stepwise approach.

The emergence of human warfare: Current perspectives

The origins of warfare have long been of interest for researchers across disciplines. Did our earliest ancestors engage in forms of organized violence that are appropriately viewed as approximations, forms of, or analogs for more recent forms of warfare? Assessed in this article are contrasting views that see warfare as being either a product of more recent human societies or a phenomenon with a much deeper chronology. The article provides an overview of current debates, theories, and methodological approaches, citing literature and data from archaeological, ethnographic, genetic, primatological, and paleoanthropological studies. Synthetic anthropological treatments are needed, especially in efforts to inform debates among nonacademic audiences, because the discipline's approaches are ideally suited to study the origins of warfare. Emphasized is the need to consider possible forms of violence and intergroup aggression within Pleistocene contexts, despite the methodological challenges associated with fragmentary, equivocal, or scarce data. Finally, the review concludes with an argument about the implications of the currently available data. We propose that socially cooperative violence, or "emergent warfare," became possible with the onset of symbolic thought and complex cognition. Viewing emergent warfare as a byproduct of the human capacity for symbolic thought explains how the same capacities for communication and sociality allowed for elaborate peacemaking, conflict resolution, and avoidance. Cultural institutions around war and peace are both made possible by these changes. Accordingly, we suggest that studies on warfare's origins should be tied to research on the advent of cooperation, sociality, and communication.

The Combinatorial Creature: Cortical Phenotypes within and across Lifetimes

The neocortex is one of the most distinctive structures of the mammalian brain, yet also one of the most varied in terms of both size and organization. Multiple processes have contributed to this variability, including evolutionary mechanisms (i.e., alterations in gene sequence) that alter the size, organization, and connections of neocortex, and activity dependent mechanisms that can also modify these same features. Thus, changes to the neocortex can occur over different time-scales, including within a single generation. This combination of genetic and activity dependent mechanisms that create a given cortical phenotype allows the mammalian neocortex to rapidly and flexibly adjust to different body and environmental contexts, and in humans permits culture to impact brain construction.

Rethinking foundations of language from a multidisciplinary perspective

The issue of language foundations has been of great controversy ever since it was first raised in Lenneberg's (1967) monograph Biological Foundations of Language. Based on a survey of recent findings relevant to the study of language acquisition and evolution, we propose that: (i) the biological predispositions for language are largely domain-general, not necessarily language-specific or human-unique; (ii) the socio-cultural environment of language serves as another important foundation of language, which helps shape language components, induce and drive language shift; and (iii) language must have coevolved with the cognitive mechanisms associated with it through intertwined biological and cultural evolution. In addition to theoretical issues, this paper also evaluates the primary approaches recently joining the endeavor of studying language foundations and evolution, including human experiments and computer simulations. Most of the evidence surveyed in this paper comes from a variety of disciplines, and methodology therein complements each other to form a global picture of language foundations. These reflect the complexity of the issue of language foundations and the necessity of taking a multidisciplinary perspective to address it.

Zoon politikon: The evolutionary origins of human socio-political systems

We deploy the most up-to-date evidence available in various behavioral fields in support of the following hypothesis: The emergence of bipedalism and cooperative breeding in the hominin line, together with environmental developments that made a diet of meat from large animals adaptive, as well as cultural innovations in the form of fire, cooking, and lethal weapons, created a niche for hominins in which there was a significant advantage to individuals with the ability to communicate and persuade in a moral context. These forces added a unique political dimension to human social life which, through gene-culture coevolution, became Homo ludens-Man, the game player-with the power to conserve and transform the social order. Homo sapiens became, in the words of Aristotle's Nicomachean Ethics, a zoon politikon.

Evolution of language: Lessons from the genome

The post-genomic era is an exciting time for researchers interested in the biology of speech and language. Substantive advances in molecular methodologies have opened up entire vistas of investigation that were not previously possible, or in some cases even imagined. Speculations concerning the origins of human cognitive traits are being transformed into empirically addressable questions, generating specific hypotheses that can be explicitly tested using data collected from both the natural world and experimental settings. In this article, I discuss a number of promising lines of research in this area. For example, the field has begun to identify genes implicated in speech and language skills, including not just disorders but also the normal range of abilities. Such genes provide powerful entry points for gaining insights into neural bases and evolutionary origins, using sophisticated experimental tools from molecular neuroscience and developmental neurobiology. At the same time, sequencing of ancient hominin genomes is giving us an unprecedented view of the molecular genetic changes that have occurred during the evolution of our species. Synthesis of data from these complementary sources offers an opportunity to robustly evaluate alternative accounts of language evolution. Of course, this endeavour remains challenging on many fronts, as I also highlight in the article. Nonetheless, such an integrated approach holds great potential for untangling the complexities of the capacities that make us human.

How can we detect when language emerged?

Views differ radically as to how deep the roots of language lie in human phylogeny, largely because prior to the development of writing systems, this striking human attribute has to be inferred from indirect proxies preserved in the material record. Here I argue that the most appropriate such archaeological proxies encode the modern human symbolic cognitive system from which language emerges. Throughout the 2.5 million years or more for which an archaeological record has existed, change has been both sporadic and rare-until symbolic objects and behaviors begin to appear, well within the tenure of our highly apomorphic species Homo sapiens. I propose that the biology underwriting our unusual cognitive and linguistic systems was acquired in the major developmental reorganization that gave rise to our anatomically distinctive species around 200,000 years ago in Africa. However, the material record indicates that this new potential lay fallow for around 100,000 years, following which it was released by what was necessarily a behavioral stimulus. By far the best candidate for that stimulus is the spontaneous invention of language, which is plausibly underwritten by a relatively simple mental algorithm, and could readily have spurred symbolic cognitive processes in a feedback process. None of this means that earlier hominid vocal communication systems were not complex, or that extinct hominid species were not highly intelligent. But it does emphasize the qualitative distinctiveness of both modern symbolic cognition and language.

Agent-based models for the emergence and evolution of grammar

Human languages are extraordinarily complex adaptive systems. They feature intricate hierarchical sound structures, are able to express elaborate meanings and use sophisticated syntactic and semantic structures to relate sound to meaning. What are the cognitive mechanisms that speakers and listeners need to create and sustain such a remarkable system? What is the collective evolutionary dynamics that allows a language to self-organize, become more complex and adapt to changing challenges in expressive power? This paper focuses on grammar. It presents a basic cycle observed in the historical language record, whereby meanings move from lexical to syntactic and then to a morphological mode of expression before returning to a lexical mode, and discusses how we can discover and validate mechanisms that can cause these shifts using agent-based models.This article is part of the themed issue 'The major synthetic evolutionary transitions'.

The Evolution of Lateralized Brain Circuits

In the vast clade of animals known as the bilateria, cerebral and behavioral asymmetries emerge against the backdrop of bilateral symmetry, with a functional trade-off between the two. Asymmetries can lead to more efficient processing and packaging of internal structures, but at the expense of efficient adaptation to a natural world without systematic left-right bias. Asymmetries may arise through the fissioning of ancestral structures that are largely symmetrical, creating new circuits. In humans these may include asymmetrical adaptations to language and manufacture, and as one or other hemisphere gains dominance for functions that were previously represented bilaterally. This is best illustrated in the evolution of such functions as language and tool manufacture in humans, which may derive from the mirror-neuron system in primates, but similar principles probably apply to the many other asymmetries now evident in a wide range of animals. Asymmetries arise in largely independent manner with multi-genetic sources, rather than as a single over-riding principle.