Hadza handedness: Lateralized behaviors in a contemporary hunter–gatherer population
Tammany Cavanagh2016, Evolution and Human Behavior
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On the other hand: Current issues in and meta-analysis of the behavioural laterality of hand function in nonhuman primates
Yearbook of Physical Anthropology, 1997
The last decade has seen a resurgence of interest in laterality of function in primates, especially in hand use as it links to handedness and language in Homo sapiens. Manual lateralization of behavior in humans reflects asymmetry in cerebral structure, which must have evolved from nonhuman progenitors. To what extent is hand function lateralized in our nearest living relations? First, we address current issues of theory and methodology: statistics, measurement, variables, setting, sensory modality, and sample size. Specific topics include preference vs. performance, posture, bimanuality, inheritance, and arm asymmetry. We categorize the published literature in a descriptive, classificatory framework of five levels that range from Level 1, ambilaterality, to Level 5, human-like handedness. In a meta-analysis we put 241 published data-sets to a methodological test of seven criteria and code the 48 survivors onto the levels framework, by taxonomic grouping (prosimian, New World monkey, Old World monkey, ape, chimpanzee). Primates at Level 1 are mostly wild or naturalistic populations performing spontaneous species-typical behavior patterns. Most primates are at Levels 2 and 3, that is, individually lateralized to either side, especially on complex, demanding or practiced tasks, usually as devised in captive settings. Only chimpanzees show signs of population-level bias (Levels 4 and 5) to the right, but only in captivity and only incompletely. We conclude that nonhuman primate hand function has not been shown to be lateralized at the species level-it is not the norm for any species, task, or setting, and so offers no easy model for the evolution of human handedness.
On which side of the apes? Ethological study of laterality of hand use
Great Ape Societies, 1996
Until 1987, the received wisdom in psychobiology was that laterality of function in Homo sapiens was unique, and so qualitatively different from all other species, including even our nearest relations, the great apes. Humans were said to be overwhelmingly right-handed at species (or population) level, that is, about 90% of persons show right-hand dominance for virtually all kinds of hand-use. In contrast, other hominoids were said to be randomly lateralized, either showing no consistent, overall preference for left or right, or being individually lateralized to either the left or right side in about equal numbers.
On the other hand: Current issues in and meta-analysis of the behavioral laterality of hand function in nonhuman primates
American Journal of Physical Anthropology, 1997
The last decade has seen a resurgence of interest in laterality of function in primates, especially in hand use as it links to handedness and language in Homo sapiens. Manual lateralization of behavior in humans reflects asymmetry in cerebral structure, which must have evolved from nonhuman progenitors. To what extent is hand function lateralized in our nearest living relations? First, we address current issues of theory and methodology: statistics, measurement, variables, setting, sensory modality, and sample size. Specific topics include preference vs. performance, posture, bimanuality, inheritance, and arm asymmetry. We categorize the published literature in a descriptive, classificatory framework of five levels that range from Level 1, ambilaterality, to Level 5, human-like handedness. In a meta-analysis we put 241 published data-sets to a methodological test of seven criteria and code the 48 survivors onto the levels framework, by taxonomic grouping (prosimian, New World monkey, Old World monkey, ape, chimpanzee). Primates at Level 1 are mostly wild or naturalistic populations performing spontaneous species-typical behavior patterns. Most primates are at Levels 2 and 3, that is, individually lateralized to either side, especially on complex, demanding or practiced tasks, usually as devised in captive settings. Only chimpanzees show signs of population-level bias (Levels 4 and 5) to the right, but only in captivity and only incompletely. We conclude that nonhuman primate hand function has not been shown to be lateralized at the species level-it is not the norm for any species, task, or setting, and so offers no easy model for the evolution of human handedness.
Handedness is more than laterality: lessons from chimpanzees
Annals of the New York Academy of Sciences, 2013
Is human handedness unique? That is, do our nearest living relations, chimpanzee and bonobo (Pan spp.) show species-wide handedness, as is seen in living Homo sapiens? The answer may depend on definition: Handedness (congruence across subjects and across tasks) should be distinguished from hand preference (within subject and task), manual specialization (within subject, across tasks), and task specialization (across subjects, within task). Comparison is required at both population and species level. Several methodological issues (e.g., ecological validity) are crucial, as are major confounding variables (e.g., bimanuality). The behavioral manual laterality of chimpanzees is well-studied in a variety of contexts. Especially important is tool use, which seems to enhance extent of lateralization, but this varies both within and across populations. There is much evidence for task specialization in chimpanzees, but no conclusive evidence of handedness in the strictest sense. Thus, human handedness seems to be unique among living hominoids.
Comparative and familial analysis of handedness in great apes
Psychological Bulletin, 2006
Historically, population-level handedness has been considered a hallmark of human evolution. Whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. This paper summarizes published data on handedness in great apes. Comparative analysis indicated that chimpanzees and bonobos show population-level right handedness, whereas gorillas and orangutans do not. All ape species showed evidence of population-level handedness when considering specific tasks. Familial analyses in chimpanzees indicated that offspring and maternal (but not paternal) handedness was significantly positively correlated, but this finding was contingent upon the classification criteria used to evaluate hand preference. Overall, the proportion of right handedness is lower in great apes compared with humans, and various methodological and theoretical explanations for this discrepancy are discussed.
Can hominin'handedness' be accurately assessed?
Annals of human biology, 2009
Chimpanzees are right‐handed when recording bouts of hand use
Laterality: Asymmetries of Body, Brain and Cognition, 2005
Whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. Previous research has shown that chimpanzees are right-handed when frequencies of hand use are recorded but some have questioned the validity of this approach. In this study, we evaluated handedness in 180 captive chimpanzees for a task measuring bimanual actions. Bouts rather than frequency of hand use were recorded in each subject. Population-level right-handedness was found using both continuous and nominal scales of measurement. Neither sex nor rearing history had a significant effect on hand use. These results indicate that chimpanzees are right-handed, even when using a more conservative measure of handedness. Limitations in the use of bouts in handedness assessment are also discussed.
RightHandedness Predominance in 162 Baboons (Papio anubis) for Gestural Communication: Consistency Across Time and Groups
Behavioral Neuroscience, 2011
Whether nonhuman primates exhibit population level right manual bias remains a controversial topic. In captive baboons, population-level right-handedness has been reported for both coordinated bimanual actions and communicative gestures. However, some authors remain skeptical of these findings on both methodological and theoretical grounds. Here, we demonstrated the robustness and the consistency across time of the pattern of right-handedness for a species-specific communicative gesture in olive baboons (Papio anubis). First, we showed significant correlations in the 26 retested baboons for the measures of hand preferences between the first and the second session conducted 4 years later (2005)(2006)(2007)(2008)(2009)) by an observer blind to the previous handedness data. Second, the replication of the study in 96 novel individuals revealed a similar degree of population-level right-handedness than the one expressed in the first group of 66 subjects investigated in 2005. The implications of the findings are discussed within a theoretical framework about the origin of hemispheric specialization for language.
Population-Level Right Handedness for a Coordinated Bimanual Task in Chimpanzees: Replication and Extension in a Second Colony of Apes
International journal of primatology, 2003
The purpose of this study was to evaluate the reliability of previously published findings on hand preferences in chimpanzees by evaluating hand use in a second colony of captive chimpanzees. We assessed hand preferences for a coordinated bimanual task in 116 chimpanzees (Pan troglodytes) at the University of Texas M. D. Anderson Cancer Center and compared them to previously published findings in captive chimpanzees at the Yerkes National Primate Research Center. The new sample showed significant population-level right handedness, which is consistent with previously published findings in the Yerkes chimpanzees. Combined data on the 2 chimpanzee colonies, revealed a significant effect of rearing history on hand preference, with wild-caught chimpanzees showing less right-handedness than captive-born mother-reared chimpanzees. We discuss the results in terms of the role of early environment on the development of laterality.
The evolution of handedness in humans and great apes: a review and current issues
Journal of anthropological sciences = Rivista di antropologia : JASS / Istituto italiano di antropologia, 2008
Population-level right-handedness is a defining characteristic of humans. Despite extensive research, we still do not know the conditions or timing of its emergence in human evolution. We present a review of research into the origins of handedness, based on fossil and archaeological data for hand preference and great ape hand-use. The data show that skeletal asymmetries in arm and hand bones supporting a rightsided dominance were present at least in the genus Homo, although data are more robust for Neanderthals. The evidence from tool-use, production, and cave art confirms that right-hand preference was established in Neanderthals and was maintained until the present. The great apes can provide real-life models for testing the conditions that facilitate or enhance hand preference at both the individual and group levels. The database on great ape hand-use indicates that they do exhibit hand preferences, especially in complex tasks. However, their preferences vary between tasks, and w...
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HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
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Royal Society Open Science
Despite significant scientific advances, the nature of the left-hemispheric systems involved in language (speech and gesture) and manual actions is still unclear. To date, investigations of human laterality focused mainly on non-communication functions. Although gestural laterality data have been published for infants and children, relatively little is known about laterality of human gestural communication. This study investigated human laterality in depth considering non-communication manipulation actions and various gesture types involving hands, feet, face and ears. We constructed an online laterality questionnaire including 60 items related to daily activities. We collected 317 594 item responses by 5904 randomly selected participants. The highest percentages of strong left-lateralized (6.76%) and strong right-lateralized participants (75.19%) were for manipulation actions. The highest percentages of mixed left-lateralized (12.30%) and ambidextrous (50.23%) participants were fou...
Did heart asymmetry play a role in the evolution of human handedness?
Journal of Cultural Cognitive Science, 2017
Almost 90% of humans are right handed, but why is unclear. It has been suggested that right handedness evolved in the context of escalating motor and cognitive demands related to tool use. Literature indicates that homicide may have been common in early hominins. Since, in combat with sharp implements, handedness may influence the relative level of exposure of left and right thorax, the hypothesis presented here is that thoracic anatomic asymmetry resulted in a survival advantage for right handed individuals. While fighting with sharp tools, a left hand unilateral grip will rotate the left hemi-thorax towards an opponent. The aims of this study were to quantify the degree of thoracic/cardiac asymmetry in humans and to estimate any difference in risk of injury from a sharp implement attack to the left and the right human thorax. CT-scans of 37 men showed a mean of 73% (SD 7%) of the heart volume to be situated in the left hemi-thorax. Nineteen physicians unaware of the hypothesis estimated the outcome of weapons penetrating the left and right thorax/abdomen at random points. The difference in estimated mortality for left and right thorax was significant, p \ 0.001 (Wilcoxon-signed-ranks-test for two related samples). These results suggest greater vulnerability of the left side of the body in combat, and, accordingly, an adaptive value of right-handedness. Thoracic asymmetry may have contributed to the development of right hand preference in humans.
Effects of Handedness and Viewpoint on the Imitation of Origami-Making
Symmetry
The evolutionary origins of the human bias for 85% right-handedness are obscure. The Apprenticeship Complexity Theory states that the increasing difficulty of acquiring stone tool-making and other manual skills in the Pleistocene favoured learners whose hand preference matched that of their teachers. Furthermore, learning from a viewing position opposite, rather than beside, the demonstrator might be harder because it requires more mental transformation. We varied handedness and viewpoint in a bimanual learning task. Thirty-two participants reproduced folding asymmetric origami figures as demonstrated by a videotaped teacher in four conditions (left-handed teacher opposite the learner, left-handed beside, right-handed opposite, or right-handed beside). Learning performance was measured by time to complete each figure, number of video pauses and rewinds, and similarity of copies to the target shape. There was no effect of handedness or viewpoint on imitation learning. However, participants preferred to produce figures with the same asymmetry as demonstrated, indicating they imitate the teacher's hand preference. We speculate that learning by imitation involves internalising motor representations and that, to facilitate learning by imitation, many motor actions can be flexibly executed using the demonstrated hand configuration. We conclude that matching hand preferences evolved due to socially learning moderately complex bimanual skills.
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On the origins of human handedness and language: A comparative review of hand preferences for bimanual coordinated actions and gestural communication in nonhuman primates
Developmental Psychobiology, 2013
Within the evolutionary framework about the origin of human handedness and hemispheric specialization for language, the question of expression of population-level manual biases in nonhuman primates and their potential continuities with humans remains controversial. Nevertheless, there is a growing body of evidence showing consistent population-level handedness particularly for complex manual behaviors in both monkeys and apes. In the present article, within a large comparative approach among primates, we will review our contribution to the field and the handedness literature related to two particular sophisticated manual behaviors regarding their potential and specific implications for the origins of hemispheric specialization in humans: bimanual coordinated actions and gestural communication. Whereas bimanual coordinated actions seem to elicit predominance of left-handedness in arboreal primates and of righthandedness in terrestrial primates, all handedness studies that have investigated gestural communication in several primate species have reported stronger degree of population-level right-handedness compared to noncommunicative actions. Communicative gestures and bimanual actions seem to affect differently manual asymmetries in both human and nonhuman primates and to be related to different lateralized brain substrates. We will discuss (1) how the data of hand preferences for bimanual coordinated actions highlight the role of ecological factors in the evolution of handedness and provide additional support the postural origin theory of handedness proposed by MacNeilage . Present status of the postural origins theory. In W. D. Hopkins (Ed.), The evolution of hemispheric specialization in primates (pp. 59-91). London: Elsevier/Academic Press] and (2) the hypothesis that the emergence of gestural communication might have affected lateralization in our ancestor and may constitute the precursors of the hemispheric specialization for language. ß 2013 Wiley Periodicals, Inc. Dev Psychobiol 55: 637-650, 2013.
Hand preferences for coordinated bimanual actions in 777 great apes: Implications for the evolution of handedness in Hominins
Journal of Human Evolution, 2011
Whether or not nonhuman primates exhibit population-level handedness remains a topic of considerable scientific debate. Here, we examined handedness for coordinated bimanual actions in a sample of 777 great apes including chimpanzees, bonobos, gorillas, and orangutans. We found population-level right-handedness in chimpanzees, bonobos and gorillas, but left-handedness in orangutans. Directional biases in handedness were consistent across independent samples of apes
Population-level right-handedness for a coordinated bimanual task in naturalistic housed chimpanzees: replication and extension in 114 animals from Zambia and Spain
American Journal of Primatology, 2011
Recently, many studies have been conducted on manual laterality in chimpanzees. Nevertheless, whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. One of the behaviors studied has been bimanual coordinated actions. Although recent studies have highlighted that captive chimpanzees show handedness at population level for these tasks, some authors have questioned the validity and consistency of these results. The first reason has been the humanization of the samples. The second one has been that the results refer to animals in American biomedical centers and the studies were conducted by the same team [WD Hopkins et al.]. This article aims to assess the laterality in bimanual coordination (tube task) activities in animals housed in an intermediate environment (Chimfunshi, Zambia). This has been conducted by replicating previous studies on similar samples (Mona Foundation, Spain), and then by extending the results to chimpanzees housed in intermediate settings. Individuals were evaluated through four experimental sessions (tests). Results indicated that 86% of the Chimfunshi sample was lateralized (48% RH, 38% LH). Furthermore, the sample showed population-level right-handedness in the mean handedness index, in Test 1, Test 2, and the first half of the study (Test 112). Rearing experience did not have an influence on hand preference. Taken together, the two sample (intermediate settings: Chimfunshi and Mona) results indicate a clear right-handedness. In conclusion, this replication and extension shows that (1) the Mona and Chimfunshi chimpanzees are right-handed in certain conditions, (2) the results are consistent with those obtained by Hopkins in captive settings, (3) the humanization of the samples does not affect manual laterality, (4) females are right-handed at population-level, but not males, and (5) these results reinforce the fact that the complexity of the task plays a dominant role in the expression of hand laterality among chimpanzees. Am. J. Primatol. 73:281-290, 2011.
A comparative assessment of handedness and its potential neuroanatomical correlates in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus)
Behaviour, 2015
The evolutionary origins of human right-handedness remain poorly understood. Some have hypothesized that tool use served as an important preadaptation for the eventual evolution of populationlevel right-handedness. In contrast, others have suggested that complex gestural and vocal communication served as prerequisite for the evolution of human right-handedness. In this study, we tested these competing hypotheses by comparing the handedness of bonobos and chimpanzees, two closely related species of Pan, on three different measures of hand use including simple reaching, manual gestures and coordinated bimanual actions. Chimpanzees are well known for their tool using abilities whereas bonobos rarely use tools in the wild. In contrast, many have suggested that bonobos have a more flexible gestural and vocal communication system than chimpanzees. The overall results showed that chimpanzees were significantly more right-handed than bonobos for all three measures suggesting that adaptations for tool use rather than communication may have led to the emergence of human right-handedness. We further show that species differences in handedness may be linked to variation in the size and asymmetry of the motor-hand area of the precentral gyrus. The results are discussed within the context of evolutionary theories of handedness, as well as some limitations in the approach to handedness measurement in nonhuman primates.
Intraspecific gestural laterality in chimpanzees and gorillas and the impact of social propensities
Brain research, 2017
A relevant approach to address the mechanisms underlying the emergence of the right-handedness/left-hemisphere language specialization of humans is to investigate both proximal and distal causes of language lateralization through the study of non-human primates' gestural laterality. We carried out the first systematic, quantitative comparison of within-subjects' and between-species' laterality by focusing on the laterality of intraspecific gestures of chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) living in six different captive groups. We addressed the following two questions: (1) Do chimpanzees and gorillas exhibit stable direction of laterality when producing different types of gestures at the individual level? If yes, is it related to the strength of laterality? (2) Is there a species difference in gestural laterality at the population level? If yes, which factors could explain this difference? During 1356 observation hours, we recorded 42335 cases of d...
Captive chimpanzees' manual laterality in tool use context: Influence of communication and of sociodemographic factors
Behavioural processes, 2018
Understanding variations of apes' laterality between activities is a central issue when investigating the evolutionary origins of human hemispheric specialization of manual functions and language. We assessed laterality of 39 chimpanzees in a non-communication action similar to termite fishing that we compared with data on five frequent conspecific-directed gestures involving a tool previously exploited in the same subjects. We evaluated, first, population-level manual laterality for tool-use in non-communication actions; second, the influence of sociodemographic factors (age, sex, group, and hierarchy) on manual laterality in both non-communication actions and gestures. No significant right-hand bias at the population level was found for non-communication tool use, contrary to our previous findings for gestures involving a tool. A multifactorial analysis revealed that hierarchy and age particularly modulated manual laterality. Dominants and immatures were more right-handed when...
Comparative Assessment of Handedness for a Coordinated Bimanual Task in Chimpanzees (Pan troglodytes), Gorillas (Gorilla gorilla), and Orangutans (Pongo pygmaeus)Descriptive Data for the Gorilla and Orangutan Samples
Hand preferences for a coordinated bimanual task were assessed in a sample of 31 captive gorillas (Gorilla gorilla) and 19 captive orangutans (Pongo pygmaeus) and were compared with chimpanzee (Pan troglodytes) hand preferences in subjects that were matched on the basis of age, sex, and rearing history. The task required that the apes remove food from the inside edges of a symmetrical polyvinyl chloride pipe presented to them in their home cages. The results indicate significant species differences with chimpanzees showing population-level right-handedness and orangutans showing population-level left-handedness. The gorillas showed a nonsignificant trend toward right-handedness. The results are discussed in terms of possible ecological or biomechanical factors that may influence hand preferences in different ape species.
History, development and current advances concerning the evolutionary roots of human right‐handedness and language: Brain lateralisation and manual laterality in non‐human primates
Ethology
This review highlights the scientific advances concerning the origins of human righthandedness and language (speech and gestures). The comparative approach we adopted provides evidence that research on human and non-human animals' behavioural asymmetries helps understand the processes that lead to the strong human left-hemisphere specialisation. We review four major non-mutually exclusive environmental factors that are likely to have shaped the evolution of human and nonhuman primates' manual asymmetry: socioecological lifestyle, postural characteristics, task-level complexity and tool use. We hypothesise the following scenario for the evolutionary origins of human right-handedness: the right-direction of modern humans' manual laterality would have emerged from our ecological (terrestrial) and social (multilevel system) lifestyle; then, it would have been strengthened by the gradual adoption of the bipedal stance associated with bipedal locomotion, and the increasing level of complexity of our daily tasks including bimanual coordinated actions and tool use. Although hemispheric functional lateralisation has been shaped through evolution, reports indicate that many factors and their mutual intertwinement can modulate human and non-human primates' manual laterality throughout their life cycle: genetic and environmental factors, mainly individual sociodemographic characteristics (e.g., age, sex and rank), behavioural characteristics (e.g., gesture per se and gestural sensory modality) and context-related characteristics (e.g., emotional context and position of target). These environmental (evolutionary and life cycle) factors could also have influenced primates' manual asymmetry indirectly through epigenetic modifications. All these findings led us to propose the hypothesis of a multicausal origin of human right-handedness.
Laterality of function in apes: a meta-analysis of methods
Journal of Human Evolution, 1991
Wild chimpanzees show population-level handedness for tool use
Proceedings of the National Academy of Sciences, 2005
Whether nonhuman primates exhibit population-level handedness remains a topic of considerable theoretical and empirical debate. One continued subject of discussion is whether evidence of population-level handedness in primates is confined to studies in captive animals or whether it is in both captive and wild subjects. Here, we report evidence of population-level handedness in wild chimpanzees for a tool-use task known as ''termite-fishing.'' We subsequently compared the handedness for termite-fishing with other published reports on handedness for nut-cracking and wadge-dipping and found task-specific differences in handedness. Last, when combing all of the published data on tool use in wild chimpanzees, we show that hand preferences are heritable. Contrary to previous claims, our results demonstrate that populationlevel handedness is evident in wild chimpanzees and suggest that the antecedents of lateralization of function associated with hand use were present at least 5 million years ago, before the Pan-Homo split.
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