Modeling Coevolution between Language and Memory Capacity during Language Origin

Memory is essential to many cognitive tasks including language. Apart from empirical studies of memory effects on language acquisition and use, there lack sufficient evolutionary explorations on whether a high level of memory capacity is prerequisite for language and whether language origin could influence memory capacity. In line with evolutionary theories that natural selection refined language-related cognitive abilities, we advocated a coevolution scenario between language and memory capacity, which incorporated the genetic transmission of individual memory capacity, cultural transmission of idiolects, and natural and cultural selections on individual reproduction and language teaching. To illustrate the coevolution dynamics, we adopted a multi-agent computational model simulating the emergence of lexical items and simple syntax through iterated communications. Simulations showed that: along with the origin of a communal language, an initially-low memory capacity for acquired linguistic knowledge was boosted; and such coherent increase in linguistic understandability and memory capacities reflected a language-memory coevolution; and such coevolution stopped till memory capacities became sufficient for language communications. Statistical analyses revealed that the coevolution was realized mainly by natural selection based on individual communicative success in cultural transmissions. This work elaborated the biology-culture parallelism of language evolution, demonstrated the driving force of culturally-constituted factors for natural selection of individual cognitive abilities, and suggested that the degree difference in language-related cognitive abilities between humans and nonhuman animals could result from a coevolution with language.     

Communication and the primate brain: insights from neuroimaging studies in humans, chimpanzees and macaques

Considerable knowledge is available on the neural substrates for speech and language from brain-imaging studies in humans, but until recently there was a lack of data for comparison from other animal species on the evolutionarily conserved brain regions that process species-specific communication signals. To obtain new insights into the relationship of the substrates for communication in primates, we compared the results from several neuroimaging studies in humans with those that have recently been obtained from macaque monkeys and chimpanzees. The recent work in humans challenges the longstanding notion of highly localized speech areas. As a result, the brain regions that have been identified in humans for speech and nonlinguistic voice processing show a striking general correspondence to how the brains of other primates analyze species-specific vocalizations or information in the voice, such as voice identity. The comparative neuroimaging work has begun to clarify evolutionary relationships in brain function, supporting the notion that the brain regions that process communication signals in the human brain arose from a precursor network of regions that is present in nonhuman primates and is used for processing species-specific vocalizations. We conclude by considering how the stage now seems to be set for comparative neurobiology to characterize the ancestral state of the network that evolved in humans to support language.     

On the Evolutionary Foundations of Language

New data on the cognitive capacities of other primates requires a reevaluation of our position on the nature of human language and the factors that led to its development. Pressures on the limited display system of the social primates may have made changes in the vocal tract anatomy of man associated with the development of upright posture of great selective importance. Human vocal tract anatomy may be at least as important as brain capacity in accounting for the origins of human language. An apparent upper age limit on efficient language acquisition in man leads to the "foreign accent" phenomenon. This may have been adoptively significant as a device which helped in the maintenance of a population structure in which rapid genetic change was possible. Embedding in language may represent a cognitive ability that is also reflected in the capacity for cultural variation, and may be extremely important in maintaining efficient population structure and in selecting for increasing intelligence.     

Language, Handedness, and Primate Brains: Did the Australopithecines Sign?

Evidence from comparative primate neuroanatomy, archaeology, and studies of vocalization systems of nonhuman primates suggests that human vocal language has a long evolutionary history and that there is continuity between our early primate ancestors' call systems and human speech. Old World monkeys exhibit cerebral asymmetries similar to those that appear related to human language. If arboreal monkeylike ancestors of humans were also characterized by cerebral asymmetry, then the fundamental asymmetry that forms the neurological substrate for human language may have been established through selection for simple "discrete" call systems in an arboreal habitat and would have occurred much longer ago than previously thought. The eventual shift from an arboreal to a terrestrial habitat was accompanied by increased complexity ("gradation") of vocal communication systems. The archaeological record of tools suggests that communication systems became still more complex under the selective pressures that led to bipedalism and that language had been selected for by the time that bipedalism was achieved. Contrary to the gestural hypothesis, right-handedness (which could not have preceded freeing of the hands) succeeded speech and may have been due to selective pressures for increased complexity of communication, causing a Field Effect upon the brain. [australopithecine, cerebral asymmetry, language, primate brains, right-handedness]     

The neural circuitry underlying primate calls and human language

There are significant structural and functional differences between primate calls and human speech. In addition, these two forms of vocal communication appear to largely depend on nonhomologous brain structures. However, an analysis of the underlying axonal circuitry of these brain systems suggests that there are significant interrelationships between them, both in functional and in evolutionary terms. Based on both primate neuroanatomical studies and humanin vivo mapping studies it is argued that the ventral prefrontal area is the critical link, both functionally and anatomically between these distinct vocal systems. A model of human brain evolution with respect to language is proposed in which limbic-midbrain vocalization circuits became progressively subordinated to the activity of prefrontal-midbrain and frontalmotor circuits for regulating facial gesture, skilled oral food manipulation, and conditional association learning. Quantitative and developmental data are used to suggest that this resulted from the relative enlargement of prefrontal areas and the consequences this has on the relative proportions of different corticomidbrain and diencephalic-midbrain projections. Although humans exhibit a significantly reduced call repertoire, it is argued that the display-vocalization circuits that play the central role in all other primate communication have neither been eliminated, supplanted nor suppressed by language systems. They have instead become integrated into the more distributed language circuits and play a ubiquitous though subordinate role in all normal language processes.     

The evolution of intelligence: adaptive specializations versus general process

Darwin argued that between-species differences in intelligence were differences of degree, not of kind. The contemporary ecological approach to animal cognition argues that animals have evolved species-specific and problem-specific processes to solve problems associated with their particular ecological niches: thus different species use different processes, and within a species, different processes are used to tackle problems involving different inputs. This approach contrasts both with Darwin's view and with the general process view, according to which the same central processes of learning and memory are used across an extensive range of problems involving very different inputs. We review evidence relevant to the claim that the learning and memory performance of non-human animals varies according to the nature of the stimuli involved. We first discuss the resource distribution hypothesis, olfactory learning-set formation, and the 'biological constraints' literature, but find no convincing support from these topics for the ecological account of cognition. We then discuss the claim that the performance of birds in spatial tasks of learning and memory is superior in species that depend heavily upon stored food compared to species that either show less dependence upon stored food or do not store food. If it could be shown that storing species enjoy a superiority specifically in spatial (and not non-spatial) tasks, this would argue that spatial tasks are indeed solved using different processes from those used in non-spatial tasks. Our review of this literature does not find a consistent superiority of storing over non-storing birds in spatial tasks, and, in particular, no evidence of enhanced superiority of storing species when the task demands are increased, by, for example, increasing the number of items to be recalled or the duration of the retention period. We discuss also the observation that the hippocampus of storing birds is larger than that of non-storing birds, and find evidence contrary to the view that hippocampal enlargement is associated with enhanced spatial memory; we are, however, unable to suggest a convincing alternative explanation for hippocampal enlargement. The failure to find solid support for the ecological view supports the view that there are no qualitative differences in cognition between animal species in the processes of learning and memory. We also argue that our review supports our contention that speculation about the phylogenetic development and function of behavioural processes does not provide a solid basis for gaining insight into the nature of those processes. We end by confessing to a belief in one major qualitative difference in cognition in animals: we believe that humans alone are capable of acquiring language, and that it is this capacity that divides our intelligence so sharply from non-human intelligence.     

Doing with less: Hominin brain atrophy

In contrast to hominin encephalization, the final Pleistocene and Holocene reduction in cranial volume has attracted very little attention and remains unexplained. Here it is examined in the light of current neuroscientific and archaeological understanding, and it is shown that the most parsimonious explanation is via the domestication hypothesis of recent humans. Accordingly, rapid atrophy of the brain is partly explained by the culturally based process of sexual selection, first detectable in late robust Homo sapiens perhaps 40,000 years ago. Furthermore it is suggested that this deleterious process of neotenization and brain atrophy was compensated for by the concurrent development of exograms, i.e. means of storing memory outside the brain. Consequently most of human memory and cultural information is now stored external to the brain, which has altered that organ significantly and facilitated a cultural complexity that would be impossible to maintain by biological memory alone. The escalating use of exograms, neotenization and reduction in cranial volume all appear to co-occur with numerous other changes to the human genome.     

Responsiveness and perceived intelligence as predictors of speech addressed to cats

Abstract

Speech addressed to a cat was examined to test whether the use of child-directed language (CDL) with a companion animal is related to perceived intelligence of a listener and/or listener responsiveness. Fifty-one undergraduates briefly entertained a cat using a toy, and the vast majority of these participants spoke to the animal. The language used was similar to CDL, and two aspects of this language (number of questions and attribution of thoughts to the animal) were positively related to ratings of the animal's intelligence. The cat's responsiveness, as measured by time spent in proximity of the participant during the interaction, was not strongly correlated with measures of speech use. The results suggest that speech used with companion animals follows a model in which the human first perceives a social interaction, and therefore uses speech. This speech is then modified, based on the perceived comprehension of the listener, regardless of who this listener may be.     

How is linguistic memory accessed? A psychophysiological approach

The role of "subvocalization" during language comprehension, especially reading, is examined. Four arguments against it having a role in accessing memory are erroneous because 1) its latency is much shorter than is conventionally stated; 2) rate of visual information processing is erroneously estimated by failing to distinguish between reading and scanning; 3) covert speech does not disappear in the competent language performer; and 4) the argument that subvocalization is an epiphenomenon is irrelevant. Rather, data support the generalization that covert speech is present during all cognitive functioning and that its specific topography is discriminatively related to the class of phoneme being processed. It is thus inferred that during cognition the speech musculature generates a phonetic code that may function to access linguistic memory. However, since there are also numerous other psychophysiologic events associated with covert speech, a multichannel processing system is hypothesized wherein speech, visual, and kinesthetic modalities interact with the brain. Illustrations are given of how this accessing model is compatible with existing holographic and feature analyzer models of memory. Data are presented that illustrate how phonetically encoded neuromuscular events can be directly measured through psychophysiologic methods. It is hypothesized that cognitive processes are generated when cybernetic neuromuscular circuits selectively interact. Consequently, all components of these neuromuscular circuits serve a function during cognition so that a role for "subvocalization" (a muscular component) cannot be ruled out in an apriori manner.     

Pleiotropy and preadaptation in the evolution of human language capacity

The capacity for spoken language in the human is a genetic trait, but the information communicated by this means is to a large extent culturally determined. Using a gene-culture coevolutionary approach, we model the hypothesis that speech evolved as a channel for the communication of adaptive cultural traits from parent to offspring. The motivation for this paper is a condition obtained previously that initial increase of communication would require at least a two-fold advantage for the transmitted trait. Here, we show that under reasonable assumptions the invasion condition becomes less stringent. In Model 1, we assume that two adaptive cultural traits can be transmitted. A gene which permits communication of the second adaptive trait. In Model 2, we assume that a related function such as greater memory capacity is a prerequisite for speech, and that this function confers an advantage independent of its association with speech. In both models we assume haploid sexual genetics and a simple scheme of vertical transmission. The stability properties of all corner and edge equilibria of the models are analyzed. The two models taken together suggest a possible scenario for the initial stages of the evolution of speech.     

The neural and cognitive correlates of aimed throwing in chimpanzees: a magnetic resonance image and behavioural study on a unique form of social tool use

It has been hypothesized that neurological adaptations associated with evolutionary selection for throwing may have served as a precursor for the emergence of language and speech in early hominins. Although there are reports of individual differences in aimed throwing in wild and captive apes, to date there has not been a single study that has examined the potential neuroanatomical correlates of this very unique tool-use behaviour in non-human primates. In this study, we examined whether differences in the ratio of white (WM) to grey matter (GM) were evident in the homologue to Broca's area as well as the motor-hand area of the precentral gyrus (termed the KNOB) in chimpanzees that reliably throw compared with those that do not. We found that the proportion of WM in Broca's homologue and the KNOB was significantly higher in subjects that reliably throw compared with those that do not. We further found that asymmetries in WM within both brain regions were larger in the hemisphere contralateral to the chimpanzee's preferred throwing hand. We also found that chimpanzees that reliably throw show significantly better communication abilities than chimpanzees that do not. These results suggest that chimpanzees that have learned to throw have developed greater cortical connectivity between primary motor cortex and the Broca's area homologue. It is suggested that during hominin evolution, after the split between the lines leading to chimpanzees and humans, there was intense selection on increased motor skills associated with throwing and that this potentially formed the foundation for left hemisphere specialization associated with language and speech found in modern humans.     

The derived FOXP2 variant of modern humans was shared with Neandertals

Although many animals communicate vocally, no extant creature rivals modern humans in language ability. Therefore, knowing when and under what evolutionary pressures our capacity for language evolved is of great interest. Here, we find that our closest extinct relatives, the Neandertals, share with modern humans two evolutionary changes in FOXP2, a gene that has been implicated in the development of speech and language. We furthermore find that in Neandertals, these changes lie on the common modern human haplotype, which previously was shown to have been subject to a selective sweep. These results suggest that these genetic changes and the selective sweep predate the common ancestor (which existed about 300,000-400,000 years ago) of modern human and Neandertal populations. This is in contrast to more recent age estimates of the selective sweep based on extant human diversity data. Thus, these results illustrate the usefulness of retrieving direct genetic information from ancient remains for understanding recent human evolution.     

Language out of Music: The Four Dimensions of Vocal Learning

A growing consensus drawing on research in a wide variety of disciplines has, over the last fifteen years or so, argued the need to revisit Darwin's conjecture of 1871 that language may be descended from an existing, musical medium of communication that developed from animal calls. This paper seeks to examine, in an extension of Hockett's analysis of the design features required for linguistic communication, the nature of the acoustic information produced and perceived in human vocalisation, and to consider the anatomical and neural mechanisms on which these depend. An attempt is made to sketch an evolutionary chronology for key prerequisites of human orality. Cross‐species comparisons are employed to illuminate the role of four acoustic variables (pitch, duration, amplitude and timbre), viewing the potential for human vocal productivity from the perspective of animal communication. Although humans are the only species to combine entrainment to pulse with attunement to precisely‐tracked pitches, we also depend both for musical interaction and the production and perception of vowel sounds on precise and conscious control of the property of timbre. Drawing on, amongst others, Scherer's analyses of emotionally triggered sounds in a variety of species, and Fernald's presentation of the similarities of infant cries and adult production of infant‐directed speech in a variety of cultures and languages, a case is made for the instinctive components of human communication being more music‐like than language‐like. In conclusion, historical and comparative data are employed to outline the adaptive and exaptive sequence by which human vocal communication evolved. The roles of selective pressures that conform to different adaptive models are compared—natural selection, sexual selection, group selection—leading to the proposal that all of these must have played their part at different stages in the process in a ‘mosaic’ model consistent with the development of other human traits.     

Evolution of the human ASPM gene, a major determinant of brain size

The size of human brain tripled over a period of approximately 2 million years (MY) that ended 0.2-0.4 MY ago. This evolutionary expansion is believed to be important to the emergence of human language and other high-order cognitive functions, yet its genetic basis remains unknown. An evolutionary analysis of genes controlling brain development may shed light on it. ASPM (abnormal spindle-like microcephaly associated) is one of such genes, as nonsense mutations lead to primary microcephaly, a human disease characterized by a 70% reduction in brain size. Here I provide evidence suggesting that human ASPM went through an episode of accelerated sequence evolution by positive Darwinian selection after the split of humans and chimpanzees but before the separation of modern non-Africans from Africans. Because positive selection acts on a gene only when the gene function is altered and the organismal fitness is increased, my results suggest that adaptive functional modifications occurred in human ASPM and that it may be a major genetic component underlying the evolution of the human brain.     

Convergent differential regulation of parvalbumin in the brains of vocal learners

Spoken language and learned song are complex communication behaviors found in only a few species, including humans and three groups of distantly related birds--songbirds, parrots, and hummingbirds. Despite their large phylogenetic distances, these vocal learners show convergent behaviors and associated brain pathways for vocal communication. However, it is not clear whether this behavioral and anatomical convergence is associated with molecular convergence. Here we used oligo microarrays to screen for genes differentially regulated in brain nuclei necessary for producing learned vocalizations relative to adjacent brain areas that control other behaviors in avian vocal learners versus vocal non-learners. A top candidate gene in our screen was a calcium-binding protein, parvalbumin (PV). In situ hybridization verification revealed that PV was expressed significantly higher throughout the song motor pathway, including brainstem vocal motor neurons relative to the surrounding brain regions of all distantly related avian vocal learners. This differential expression was specific to PV and vocal learners, as it was not found in avian vocal non-learners nor for control genes in learners and non-learners. Similar to the vocal learning birds, higher PV up-regulation was found in the brainstem tongue motor neurons used for speech production in humans relative to a non-human primate, macaques. These results suggest repeated convergent evolution of differential PV up-regulation in the brains of vocal learners separated by more than 65-300 million years from a common ancestor and that the specialized behaviors of learned song and speech may require extra calcium buffering and signaling.     

Genetic explorations of recent human metabolic adaptations: hypotheses and evidence

Since humans and chimpanzees split from a common ancestor over 6 million years ago, human metabolism has changed dramatically. This change includes adaptations to a high-quality diet, the evolution of an energetically expensive brain, dramatic increases in endurance abilities, and capacity for energy storage in white adipose tissue. Human metabolism continues to evolve in modern human populations in response to local environmental and cultural selective forces. Understanding the nature of these selective forces and the physiological responses during human evolution is a compelling challenge for evolutionary biologists. The complex genetic architecture surrounding metabolic phenotypes indicates that selection probably altered allelic frequencies across many loci in populations experiencing adaptive metabolic change to fit their environment. A recent analysis supports this hypothesis, finding that classic selective sweeps at single loci were rare during the past 250 000 years of human evolution. Detection of selective signatures at multiple loci, as well as exploration of physiological adaptation to environment in humans, will require cross-disciplinary collaboration, including the incorporation of biological pathway analysis. This review explores the Thrifty Genotype Hypothesis, high-altitude adaptation, cold-resistance adaptation, and genetic evidence surrounding these proposed metabolic adaptations in an attempt to clarify current challenges and avenues for future progress.     

Cultural evolution: implications for understanding the human language faculty and its evolution

Human language is unique among the communication systems of the natural world: it is socially learned and, as a consequence of its recursively compositional structure, offers open-ended communicative potential. The structure of this communication system can be explained as a consequence of the evolution of the human biological capacity for language or the cultural evolution of language itself. We argue, supported by a formal model, that an explanatory account that involves some role for cultural evolution has profound implications for our understanding of the biological evolution of the language faculty: under a number of reasonable scenarios, cultural evolution can shield the language faculty from selection, such that strongly constraining language-specific learning biases are unlikely to evolve. We therefore argue that language is best seen as a consequence of cultural evolution in populations with a weak and/or domain-general language faculty.     

Are languages really independent from genes? If not, what would a genetic bias affecting language diversity look like?

It is generally accepted that the relationship between human genes and language is very complex and multifaceted. This has its roots in the “regular” complexity governing the interplay among genes and between genes and environment for most phenotypes, but with the added layer of supraontogenetic and supra-individual processes defining culture. At the coarsest level, focusing on the species, it is clear that human-specific--but not necessarily faculty-specific--genetic factors subtend our capacity for language and a currently very productive research program is aiming at uncovering them. At the other end of the spectrum, it is uncontroversial that individual-level variations in different aspects related to speech and language have an important genetic component and their discovery and detailed characterization have already started to revolutionize the way we think about human nature. However, at the intermediate, glossogenetic/population level, the relationship becomes controversial, partly due to deeply ingrained beliefs about language acquisition and universality and partly because of confusions with a different type of gene-languages correlation due to shared history. Nevertheless, conceptual, mathematical and computational models--and, recently, experimental evidence from artificial languages and songbirds--have repeatedly shown that genetic biases affecting the acquisition or processing of aspects of language and speech can be amplified by population-level intergenerational cultural processes and made manifest either as fixed “universal” properties of language or as structured linguistic diversity. Here, I review several such models as well as the recently proposed case of a causal relationship between the distribution of tone languages and two genes related to brain growth and development, ASPM and Microcephalin, and I discuss the relevance of such genetic biasing for language evolution, change, and diversity.