Archaeologists have long been preoccupied with the theoretical linkage between two features of humanity: language and right-handedness. The current view is that they evolved together, but the exact nature of this relation is still unknown. In archaeological and human origins research, it remains hypothetical. Since the last 150 years many ideas about the links between language and laterality have been proposed from other disciplines. They have primarily focused on the brain, but other areas such as primatology, developmental psychology, and ethnography have recently contributed. Interestingly, hardly any of these proposals have been systematically tested with the archaeological or fossil records. Despite directly referring to human evolution, the research is often disconnected from archaeology.
This session aims to bring together, for the first time at TAG, researchers from the diverse disciplines interested in the origins and evolution of right-handedness and language. The main focus will be on the theoretical connection between these two features regarding extinct humans. Specifically, discussions will aim to resolve the data needed to support or reject the different hypothesised linking mechanisms for the co-evolution of language and right-handedness. We invite papers that present data relevant to the different theories, for example on gestural communication, primate hand preference, human hand preference in anthropological or experimental settings, lateralised brain development and function, signs of mental health problems or language deficits in prehistoric populations (as related to poor lateralisation), laterality in language function and structure, and archaeological or palaeoanthropological evidence for prehistoric laterality or language.
New Approach To The Study Of Laterality In Flakes
Speakers: Eder Dominguez-Ballesteros (Universidad del Pais Vasco/Euskal Herriko Unibertsitatea) & A. Arrizabalaga (Universidad del Pais Vasco/Euskal Herriko Unibertsitatea)
The first studies to determine laterality and based on the production of lithic tools were published by Toth in 1985. He studied the position of the cortex on flakes. In his article he makes the assumption that a right-handed knapper rotates the core in a clockwise direction and a left-hander rotates counterclockwise. Later, Pobiner (1999) proved that this condition is not universal and that there are right-handed people who rotate the core counterclockwise and viceversa.
Subsequently, Rugg & Mullane (2001) published an article where they related the
percussion angle to the orientation of the bulb of percussion. This angle depends on the
hand used to hit the core. In their study, they obtained interesting results.
We think that the correct way to determine the knapper’s laterality should be based
on the percussion angle, like Rugg and Mullane suggested in their article, and not on
knapping habits. We propose a group of characteristics observed in flakes, related to the striking platform, that provide information about the laterality of the knapper. These characteristics depend on the percussion angle, directly related to the hand used by the knapper to hit the core.
Whole forelimb skeletal asymmetry among modern humans & great apes: Implications for the origins of handedness
Speakers: Tom Davies (University of Cambridge), Lauren Sarringhaus (University of Michigan), Colin N. Shaw (University of Cambridge) & Jay T. Stock (University of Cambridge)
The correspondence between bilateral asymmetry in mechanical properties of human metacarpals and hand preference is well established from radiogrammetric studies. Archaeological analyses of human remains demonstrate that morphological asymmetry is found throughout the upper limb. Human hunter-gatherers show predominant right limb dominance in 70% of individuals. The first study of bilateral asymmetry of long-bones among chimpanzees by Sarringhaus and colleagues in 2005 noted approximately 70% of adults featured stronger metacarpals of the right hand, while a similar number had stronger left humeri, suggesting differing influences of both manipulatory and postural behaviour on the mechanics of the skeleton. This study provides the first systematic exploration of variation in bone strength throughout the limb, using three-dimensional laser scanning to quantify bone rigidity at 1% intervals of length of the clavicles, humeri, ulnae and radii of Pan troglodytes, Gorilla gorilla, Pongo pygmaeus, and Homo sapiens. Pan and Pongo show variable levels of loading with evidence for laterality, either right or left, whilst Gorilla show only minimal asymmetry. The results are interpreted in the context of characteristics of hand preference and habitual locomotion, and have implications for understanding brain lateralisation.
Asymmetry & symmetry-breaking in Acheulean hand-axes – an exploration.
Speaker: John Gowlett (University of Liverpool)
Acheulean hand-axes are conventionally thought of as symmetrical, but some authors believe they can find little evidence of deliberately imposed symmetry in bifaces. The possible complications are not worked through in most arguments – for example, a cobble blank might well have a natural symmetry, which would then transfer through to the finished object. In some cases, however, we may NOT observe symmetry, because the toolmakers are interested in making asymmetric pieces. This paper presents a preliminary analysis of metrical data about symmetry, and argues that a slight asymmetry may often have been preferred. The general state of finish of the artefact series is seen to be one significant issue – whether symmetrical or asymmetrical, better-finished hand-axe series seem to present stronger patterns. In general, symmetry or asymmetry are likely to be preferred according to functional advantages, but if these are slight, a locally preferred tradition could emerge for non-functional or stylistic reasons.
Articulatory capacity of Neanderthals, a very recent, human-like & predominantly right-handed fossil hominin.
Speakers: Anna Barney, Sandra Martelli, Antoine Serrurier & James Steele (University College London)
There is archaeological and fossil anatomical evidence of population-level right-handedness in tool-use in Homo heidelbergensis, Neanderthals and anatomically modern Homo sapiens; these hominins are all relatively large-brained. There is also suggestive evidence of speech-relevant adaptations in the same three species in hyoid bone morphology, in the shape of the thoracic spinal canal, and – for Neanderthals – in their DNA (the presence of the human form of FOXP2). Thus, we have no a priori reason to doubt that Neanderthals had at least reached the vocal protolanguage stage of language evolution. However, the level of grammatical structure of Neanderthal vocal utterances remains speculative: we do not know whether or not the required biological and/or cultural preconditions were in place for the stable cultural evolution of linguistic structure and usage as seen in human societies today. In this paper, we shall focus instead on methods for assessing fossil evidence for the evolution of the vocal tract, one factor in assessing Neanderthals’ potential capacity for articulate speech.
Rapid cerebral hemodynamic modulation during cognitive tasks: Inferring neural networks from analysis of lateralisation data.
Speakers: Georg Meyer (University of Liverpool), Natalie Uomini (University of Liverpool) & Sophie Wuerger
We hypothesised that individual hemodynamic responses (the task specific changes in cerebral blood-flow and lateralisation, measured with transcranial Doppler ultrasound) are highly correlated in tasks that draw in similar cerebral areas, while response patterns for tasks that draw on different networks are uncorrelated.
In a first experiment we measured flood flow lateralisation patterns in three tasks: cued word generation, music synthesis and an abstract manipulation task (Tower of London, ToL). fMRI data for these tasks shows that language and music draw on very similar networks, while the TOL task uses different brain areas. We correlated individual hemodynamic response patterns for 26 participants for these tasks and show that patterns for language and music, but not for language and ToL, are highly correlated, and suggest that common underlying processing networks lead to common activation patterns.
In a second experiment we recorded hemodynamic responses during a flint knapping and a language task to test whether both tasks draw on common resources. We find that flint knapping and language are highly correlated during the initial phase of tool-use, which is consistent with theories that postulate common networks, and perhaps common evolution, of language and tool-use.
The Right-Hand Man: Language & Manual Laterality
Speaker: Gillian Forrester (University of Westminster)
Investigations of human laterality suggest motor preference is not arbitrary, but rather represents an evolutionary bias stemming from the asymmetric organization of underlying neural function for skilled action. The most prominent manifestation of lateralized motor behavior in humans is right-handedness. While human right-handedness provides a highly reliable marker for the brain organization of left hemisphere language function, the causal evolutionary link between the two remains highly controversial. Once considered a unique hallmark of human evolution, structural neuroanatomical investigations have now revealed homologous asymmetric language regions (larger left hemisphere) in great apes, providing evidence for a common mechanism underlying communication processes in humans and apes. However, whether this translates into a handedness bias in great apes remains highly controversial. This presentation will discuss the unique characteristics of human and non-human primate handedness within an evolutionary framework and explores new manual laterality findings, celebrating the emergence of multimodal, quantitative methodologies aimed at bridging the gap between studies of brain and behavior.
Brain microcircuits & lateralisation in chimpanzees & humans
Speaker: Steven Chance (University of Oxford)
The cerebral cortex is not an undifferentiated, homogenous network but appears to consist of multiple, small, structural micro-circuits. The developmental and evolutionary expansion of cortical size depends on the number and spacing of these units. Detailed study reveals differences in disorders such as autism, as well as contrasts between humans and chimpanzees. These differences relate to aspects of cognition.
Brain asymmetries have been linked to language lateralisation in the auditory domain: wider connective spacing among micro-circuits in the planum temporale of the human left hemisphere is not found in other primates. In the visual domain, better literacy in humans enhances left hemisphere activation, inducing competition with brain regions otherwise involved in face processing. Subsequently, word recognition is lateralised to the left hemisphere whereas face recognition is lateralised to the right hemisphere. Here we investigate whether asymmetrical micro-circuits may contribute to this lateralisation in the visual domain, and whether similar asymmetries are found in the chimpanzee face-associated region, partly addressing Darwin’s suggestion of a widespread biological basis for communication using facial expression.
Developments in MRI analysis offering new ways to measure these micro-circuits in vivo will also be discussed.
Speaker: Stuart J Leask (University of Nottingham)
The study of laterality often generates laterality indices, in attempts to simplify the bivariate construct (laterality) to a single variable. In this talk I explore how using laterality indices can be very misleading, and how even sticking with measures from each side can be problematic. The talk finishes with an example of the benefits of presenting the relationship between measures of hand skill and word-finding ability without laterality indices, from a birth cohort dataset, n~11,000.
What were the selection mechanisms for the genes for handedness & language dominance?
Speaker: Chris McManus (University College London)
Ten per cent or so of people in Western populations are left-handed, with somewhat lower proportions in non-Western populations. Left-handers are present in all societies, with rates never seeming to rise above about 14-15%. Such stability of the handedness polymorphism must be maintained by some mechanism. If, as seems to be the case, handedness and language dominance are probably under the control of a single gene, then there must be selective advantages for the genes (or random drift would eliminate one or other from the population). Within classical population genetics, polymorphisms can be maintained by heterozygote advantage, frequency-dependent selection, or new mutation, although the latter is unlikely given the high rates of left-handedness. Heterozygote advantage seems the most likely mechanism, either alone, or perhaps with frequency-dependent selection for genotypes. A feature of genetic models of handedness (such as the McManus DC model), is that there is no net benefit of right-handed or left-handed as such, the advantages having to be at the genotypic level. The DC model also involves random processes, with potentially many phenotypes arising from a single genotype. Some phenotypes with relatively minor alterations of cortical organisation could result either in special talents or specific deficits. However, talents, such as poetry, music, craftsmanship, or whatever, typically survive and prosper only within social organisations, and hence inevitably are more beneficial at lower frequencies (and a society comprising mostly musicians but hardly anyone growing food, is unlike to survive).
Classifying Handedness in Spontaneous Situations
Speakers: David P. Carey (Bangor University) & Patricia E.G. Bestelmeyer (Bangor University)
Handedness research has been plagued by arguments about whether preference (as estimated by questionnaire) or performance is a better predictor of underlying cerebral lateralisation. Remarkably, little is known about how often and for what each hand is used in unconstrained, everyday situations. This absence makes comparisons with non-human primate handedness research difficult. We have developed a coding scheme which allows for reliable classification of hand actions using 40 action codes under 8 main categories (reaching and grasping, manipulation, gesture, self touching, touching others, hitting, covering). Data from actors will be compared with participants in reality TV programs where choreography or excessive reshooting of scenes (which might weaken handedness estimates in the actors) could not be nuisance variables. We will compare our data with that of Marchant et al. (1995, Ethology 101) who used a different coding scheme with archived film of three hunter-gather societies. Implications for laterality research in anthropology and psychology will be discussed.