Hand preferences in captive gorillas,orang-utans and gibbons

Hand preference was assessed in 12 gorillas (Gorilla gorilla gorilla), 13 orang-utans (Pongo pygmaeus abelii), and 9 gibbons (Hylobates lar) by using a floor retrieval task and a mesh retrieval task. Hand preference was also assessed in 8 gorillas and 8 orang-utans by using a task involving the unfastening of a hasp. A bipedal requirement during testing (mesh retrieval task) facilitated detection of hand preferences. A significant left-hand preference was found for the gibbons with 6 of 6 gibbons preferring their left hand on the mesh retrieval task. Similarly, a significant right-hand preference was found for the gorillas with 10 of 12 gorillas preferring their right hand on the mesh retrieval task. The data for the orang-utan suggest a bimodal distribution on all tasks. Since the gibbon and gorilla in the wild engage in bipedal locomotion more frequently than the orangutan, one possible interpretation for these results correlates the degree of bipedal behavior of a species in its natural environment with its readiness to exhibit a unilateral population-level hand preference.     

秦岭川金丝猴的一种自发性双足姿势的脚偏好

与手偏好相比较,脚偏好被认为是研究大脑半球中语言功能偏侧性调控表达的一种更佳的行为预测指标。当前国际科学界对于人类大脑半球功能不对称性和肢体偏好进化起源的关注,有力地推动了非人灵长类物种肢体偏好行为学研究,其中关于树栖灵长类物种的相关研究,对身体姿势在灵长类肢体偏好表达的理解有十分关键作用。川金丝猴(Rhinopithecus roxellana)是我特有濒危灵长类物种,主要营树栖生活。本研究首次关注秦岭川金丝猴自发性非移动双足姿势(双足叠放)的脚偏好。研究发现在个体水平上每个焦点动物均表现出明显的脚偏好,在群组水平上表现出显著的右脚偏好,脚偏好表达无显著性别差异,其研究结果支持“姿势起源理论”。本文首次呈现野生旧大陆猴物种群组水平脚偏好的研究证据。     

Brief communication: Locomotor limb preferences in captive chimpanzees (Pan troglodytes): implications for morphological asymmetries in limb bones

Understanding the evolutionary origins of hemispheric specialization remains a topic of considerable interest in a variety of scientific disciplines. Whether nonhuman primates exhibit population-level limb preferences continues to be a controversial topic. In this study, limb preferences for ascending and descending locomotion were assessed as a means of examining the hypothesis that asymmetries in forelimb bones might be attributed to asymmetries in posture. The results indicated that captive chimpanzees showed a population-level leftward asymmetry in descending locomotion but no group bias for ascending locomotion. The results are consistent with previous behavioral studies in captive chimpanzees as well as studies on skeletal asymmetries of the forelimbs of chimpanzees.     

Manual lateralization in wild redfronted lemurs (Eulemur rufifrons) during spontaneous actions and in an experimental task

The dominant use of one hand is a striking feature of humans, but manual lateralization can be found in a variety of other species as well. In primates, the lateralization in hand use varies among species and several theories such as the “postural origin,” “task complexity,” or “development theory” have been suggested to explain this variation. In order to contribute comparative data on this phenomenon from a basal primate, we studied manual lateralization in wild redfronted lemurs (Eulemur rufifrons). Data were collected on four groups at Kirindy Forest, western Madagascar, during spontaneous actions and by confronting them with artificial feeding boxes. The lemurs did not exhibit manual lateralization on a group level in either condition. More individuals showed a hand preference in the experimental task, and the preferences were stronger compared to spontaneous actions. The direction of individual hand preferences was not consistent across the two conditions. The results of this study show that measuring manual laterality in different contexts can yield different results. Manual lateralization in wild redfronted lemurs therefore seems to be flexible and situation dependent and probably not ecologically relevant in their natural habitat. Am J Phys Anthropol 153:61–67, 2014. © 2013 Wiley Periodicals, Inc.     

Hand Preference for a Novel Bimanual Coordinated Task During Termite Feeding in Wild Western Gorillas (<Emphasis Type="Italic">Gorilla gorilla gorilla</Emphasis>)

Although the level of handedness in humans varies cross-culturally, humans are generally described as right-handed, which has been considered a uniquely human trait. Recently, captive chimpanzees (Pan troglodytes) have been shown to exhibit right-hand preference when performing bimanual but not unimanual tasks. Less clear is whether this pattern also occurs in wild chimpanzees and other African apes. Using videos (N = 49) of six wild western gorillas (Gorilla gorilla gorilla) feeding on termites at the Mondika Research Center (Republic of Congo), we tested whether they exhibit hand preference when performing unimanual, i.e., reaching for termite mound pieces; bimanual, i.e., “termite tapping”: rhythmically shaking a piece of termite mound with the dominant hand and collecting the termites in the other hand tasks; or hand transfer prior to bimanual tasks, i.e., transferring a piece of termite mound from one hand to the other. All individuals exhibited exclusive hand preference when performing the bimanual tasks, with five of six gorillas preferring the right hand. Conversely, most individuals did not show any manual preference during the unimanual task. In addition, hand preference during hand transfer revealed clear hand dominance of similar strength and direction of those shown for the bimanual task, suggesting that this measure is as sensitive as the bimanual task itself. Thus, we propose “termite feeding” as a novel task to be considered in future hand-preference studies in wild western gorillas. Our results are in concordance with those for chimpanzees and captive gorillas showing hemispheric specialization for bimanual actions in apes.     

Lateralization in feeding is food type specific and impacts feeding success in wild birds

Current research suggests that hemispheric lateralization has significant fitness consequences. Foraging, as a basic survival function, is a perfect research model to test the fitness impact of lateralization. However, our understanding of lateralized feeding behavior is based predominantly on laboratory studies, while the evidence from wild animals in natural settings is limited. Here we studied visual lateralization in yellow‐footed green pigeons (Treron phoenicoptera) feeding in the wild. We aimed to test whether different types of food objects requiring different searching strategies elicit different eye/hemisphere biases. When feeding on relatively large, uniformly colored food objects (mahua flowers) which can be present or absent in the viewed patch, the majority of pigeons relied mostly on the left eye–right hemisphere. In contrast, when feeding on smaller and more abundant food objects, with color cues signaling its ripeness (sacred figs), right‐eye (left‐hemisphere) preference prevailed. Our results demonstrate that oppositely directed visual biases previously found in different experimental tasks occur in natural feeding situations in the form of lateralized viewing strategies specific for different types of food. The results suggest that pigeons rely on the hemisphere providing more advantages for the consumption of the particular type of food objects, implying the relevance of brain lateralization as a plastic adaptation to ecological demands. We assessed the success of food discrimination and consumption to examine the link between lateralization and cognitive performance. The use of the preferred eye resulted in better discrimination of food items. Discrimination accuracy and feeding efficiency were significantly higher in lateralized individuals. The results showed that visual lateralization impacted pigeons’ feeding success, implicating important fitness benefits associated with lateralization.     

Handedness in nature: first evidence on manual laterality on bimanual coordinated tube task in wild primates

Handedness is a defining feature of human manual skill and understanding the origin of manual specialization remains a central topic of inquiry in anthropology and other sciences. In this study, we examined hand preference in a sample of wild primates on a task that requires bimanual coordinated actions (tube task) that has been widely used in captive primates. The Sichuan snub-nosed monkey (Rhinopithecus roxellana) is an arboreal Old World monkey species that is endemic to China, and 24 adult individuals from the Qinling Mountains of China were included for the analysis of hand preference in the tube task. All subjects showed strong individual hand preferences and significant group-level left-handedness was found. There were no significant differences between males and females for either direction or strength of hand preference. Strength of hand preferences of adults was significantly greater than juveniles. Use of the index finger to extract the food was the dominant extractive-act. Our findings represent the first evidence of population-level left-handedness in wild Old World monkeys and broaden our knowledge on evaluating primate hand preference via experimental manipulation in natural conditions.     

Hand preferences in captive orangutans (Pongo pygmaeus)

The strength of the evidence for population-level handedness in the great apes is a topic of considerable debate, yet there have been few studies of handedness in orangutans. We conducted a study of manual lateralization in a captive group of eight orangutans (Pongo pygmaeus) ranking the degrees of manual preference according to a defined framework. We analyzed five behavioral patterns: eat (one- and two-handed), make/modify tool, oral tool-use, and manual tool-use. Although some individuals showed significant manual preferences for one or more tasks, at the group-level both one-handed and two-handed eating, oral tool-use, and make/modify tool were ranked at level 1 (unlateralized). Manual tool-use was ranked at level 2, with four subjects demonstrating significant hand preferences, but no group-level bias to the right or left. Four subjects also showed hand specialization to the right or left across several tasks. These results are consistent with most previous studies of manual preference in orangutans. The emergence of manual lateralization in orangutans may relate to more complex manipulative tasks. We hypothesize that more challenging manual tasks elicit stronger hand preferences.     

The sound of one-hand clapping: handedness and perisylvian neural correlates of a communicative gesture in chimpanzees

Whether lateralization of communicative signalling in non-human primates might constitute prerequisites of hemispheric specialization for language is unclear. In the present study, we examined (i) hand preference for a communicative gesture (clapping in 94 captive chimpanzees from two research facilities) and (ii) the in vivo magnetic resonance imaging brain scans of 40 of these individuals. The preferred hand for clapping was defined as the one in the upper position when the two hands came together. Using computer manual tracing of regions of interest, we measured the neuroanatomical asymmetries for the homologues of key language areas, including the inferior frontal gyrus (IFG) and planum temporale (PT). When considering the entire sample, there was a predominance of right-handedness for clapping and the distribution of right- and left-handed individuals did not differ between the two facilities. The direction of hand preference (right- versus left-handed subjects) for clapping explained a significant portion of variability in asymmetries of the PT and IFG. The results are consistent with the view that gestural communication in the common ancestor may have been a precursor of language and its cerebral substrates in modern humans.     

The costs of hemispheric specialization in a fish

Laboratory and field studies have documented better cognitive performance associated with marked hemispheric specialization in organisms as diverse as chimpanzees, domestic chicks and topminnows. While providing an evolutionary explanation for the emergence of cerebral lateralization, this evidence represents a paradox because a large proportion of non-lateralized (NL) individuals is commonly observed in animal populations. Hemispheric specialization often determines large left–right differences in perceiving and responding to stimuli. Using topminnows selected for a high or low degree of lateralization, we tested the hypothesis that individuals with greater functional asymmetry pay a higher performance cost in situations requiring matching information from the two eyes. When trained to use the middle door in a row of a nine, NL fish correctly chose the central door in most cases, while lateralized fish showed systematic leftward or rightward biases. When choosing between two shoals, each seen with a different eye, NL fish chose the high-quality shoal significantly more often than the lateralized fish, whose performance was affected by eye preference for analysing social stimuli. These findings suggest the existence of a trade-off between computational advantages of hemispheric specialization and the ecological cost of making suboptimal decisions whenever relevant information is located on both sides of the body.     

Lateral bias in feeding and brachiation inHylobates

Lateralized hand use in gibbons was assessed for both food reaching and leading limb in brachiation. Sex and age effects were found in hand preference for food reaching. Adult females were all very strongly right hand preferent, whereas adult males had no across group consistent preference. Within the female group there was a strong correlation between age and strength of right handedness. When compared in terms of absolute strength of hand preference, females were found to be more strongly lateralized than males. Leading limb preference in brachiation was scored into vocal and non-vocal categories. Three subjects had a shift in preferred leading limb from the non-vocal brachiation condition to the vocal brachiation condition. This shift may be influenced by the arousal effects of species typical vocalization. The results of this study underline the importance of consideration of such factors as sex and age when interpreting behavioral lateralization data. The exploration of laterality in many different response measures is important to the achievement of a complete understanding of behavioral lateralization in primates.     

A report of behavioral lateralization in an infant orang-utan (Pongo pygmaeus)

The limb used to perform seven common activities was recorded during weekly observations of an infant orang-utan. For five of these behaviors, preferences were found that remained consistent in their direction, although there were week to week fluctuations in magnitude. Most notably, a right hand preference was found for nonfood reaching and a right hindlimb preference appeared for initiating locomotion. Although initially, food reaching was predominantly with the right hand, a shift toward preferential left hand use occurred during the final weeks of the study. Additionally, a left hand preference appeared when the infant touched either its body or head.     

Patterns of hand and mouth lateral biases in bamboo leaf shoot feeding and simple food reaching in the gentle lemur (Hapalemur griseus)

Lateralized feeding behaviors of 7 wild-born and 6 captive-born Hapalemur griseus sp. were evaluated in two conditions, simple food reaching and species-typical bamboo foraging. Gentle lemurs were found to have the strongest lateral hand preference in simple food reaching of any prosimian species yet studied. However in this small sample, population-level lateralization was not found: 5 preferred the right hand and 8 the left. The movement pattern used by hapalemurs when feeding on bamboo leaf shoots was categorized into four components: PULL IN, COUNTERFORCE, TURN, and FEED IN. Lateral hand bias was scored for all four components and lateral mouth preference was scored for the two components that involved the mouth (COUNTERFORCE and FEED IN). Strong positive correlations were found between hand preference in the most lateralized components of shoot eating (TURN and FEED IN) and simple food reaching. This suggests that the gentle lemurs' species-typical bamboo feeding behavior may contribute to the exceptionally strong hand preference for simple food reaching seen in this species. There were negative correlations between the component measure of shoot feeding that required strength (COUNTERFORCE) and the components that required manipulation (TURN and FEED IN). Within the COUNTERFORCE and FEED IN components, mouth preference and hand preference were positively associated in a manner that suggested one side of the mouth was preferred for removing the shoot and the other side for mastication. Asymmetrical dental wear may provide a means of dating behavioral lateralization in ancestral species. © 1993 Wiley-Liss, Inc.     

Lateralized tool use in wild New Caledonian crows

Many vertebrate species exhibit sensory and motor asymmetries. Laterality studies of tool use have focused on primates, where hemispheric asymmetries, manifested behaviourally in hand preferences, are thought to be associated with complex motor tasks. Here we report strong individual lateralization for tool use in birds. New Caledonian crows, Corvus moneduloides, hold stick tools with their bills while foraging, often with the nonworking end laterally positioned on one side of the head and the working end possibly positioned in the binocular field. We observed four wild crows to determine whether tools were consistently held on one side. All crows showed a significant preference (two right, two left). This preference was independent of any asymmetry in tool manufacture and held for artificial holes similarly accessible for tools held on either side. This is the first demonstration of lateralized tool use in a nonprimate. In addition, all 173 tools used unilaterally were held only on a crow's preferred side. Such pronounced individual laterality for tool use in natural conditions has previously been reported only in humans and chimpanzees.     

True handedness in the cotton-top tamarin (Saguinus oedipus)?

Hand use for 8 activities was studied in 20 captive cotton-top tamarins (Saguinus oedipus). The purpose of the study was to discover if hand preferences existed across tasks and across subjects, and, if so, whether these followed the patterns of preference inMacNeilage et al.'s (1987) “postural origins” theory of the evolution of hand preference and hemispheric specialization in primates. This theory suggests that, for haplorines, the right hand is used preferentially for manipulative acts while the left hand is used preferentially for visually guided acts. The study showed statistically significant right hand preferences for six of the seven actions which produced sufficient data to be tested. The strength and consistency of this preference makes this study the first to suggest true handedness in a non-human primate species. Deviations from the pattern were seen in scratching and other actions when performed in a vertical posture, but these deviations took the form of a weakening of the right hand preference rather than a reversal. The findings of the study may be seen as supportingMacNeilage et al.'s (1987) theoryonly if the actions studied are all considered to be manipulative, which can be argued to be the case, though some of the actions were also visually guided.     

Patterns of lateralized hand use in an arboreal primate, Simias concolor

Studies of hand use in nonhuman primates suggest that several species exhibit hand preferences for a variety of tasks. The majority of studies, however, focus on the lateralized hand use of captive nonhuman primate populations. Although captive settings offer a more controlled environment for assessing hand preferences, studies of wild populations provide important insights into how handedness is affected by natural environmental conditions and thus potential insights into the evolution of handedness. To investigate handedness in a population of wild nonhuman primates, we studied patterns of lateralized hand use during feeding in four simakobu monkeys (Simias concolor), an arboreal species inhabiting the Mentawai Islands, Indonesia. Our data show that individual variation in hand preferences for feeding existed among our study animals. In addition, each simakobu expressed a significant hand preference for supporting itself on a branch during feeding, an uncoordinated bimanual task. This bias was most prevalent when the branch used for support was a main branch rather than a terminal branch. When both hands were employed in a coordinated bimanual feeding activity (bimanual manipulation), only two subjects showed a significant bias for feeding. Our data suggest that these individuals are more likely to express significant hand preferences when feeding from stable, rather than precarious, positions within the canopy.     

Manual lateralization in early primates: a comparison of two mouse lemur species

In humans, 90% of the population is right handed. Although population hand preference has been found in some primate species, the evolution of manual lateralization in primates is not yet clear. To gain insight into manual lateralization of ancestral primates, we studied hand usage in unspecialized quadrupedal, nocturnal lemurs, using a large sample size. We compared two closely related mouse lemur species to explore the variation of hand preference within the same genus. We tested 44 gray mouse lemurs and 19 Goodman's mouse lemurs in a forced food grasping task. The tests were videotaped. Measures of hand preference (i.e. the hand that is spontaneously chosen for a specific task) and successful hand usage (i.e. the hand that is successful in completing a specific task) were taken to explore manual lateralization. Both species showed manual lateralization at an individual, but not at a population level. Goodman's mouse lemurs showed stronger individual hand preferences than gray mouse lemurs. This suggests that strength in hand preference is variable within the same genus. No sex and age effects were found. The hand preference of offspring was negatively correlated to that of their mothers, but not correlated to that of their fathers. Thus, no clear genetic effect can be derived from these results. In the Goodman's mouse lemurs, hand preference increased with increasing task experience. However, successful hand usage was not affected by task experience, suggesting that successful hand usage is a more stable measurement for manual lateralization than hand preference.     

Observations of hand preference in wild groups of white-faced sakis (Pithecia pithecia) in Suriname

Hand preference is well observed in humans and some primates. Unlike many other primates, however, humans show a consistent hand preference across a variety of tasks, and a distinct right-handed skew at the population level. Although there are a moderate number of published studies, primate hand preference literature is unbalanced by the large number of studies on only a few species. No previous studies have addressed hand preference in white-faced sakis (WFS; Pithecia pithecia). We followed three habituated groups of wild WFS in Suriname and recorded individual hand preference for six different manual behaviors. There was no consistent hand preference across a range of uni-manual behaviors for any individual. Likewise, there were significantly more ambidextrous individuals in the population than expected (χ(2) (df = 2) = 11.2, P = 0.004) and thus, no population level hand preference. Our findings contribute baseline data to the debate of primate hand lateralization, and support the notion that lateralization of hand function does not characterize all species.     

Handedness in great apes: A review of findings

We present data on hand preference in great apes and discuss them in the context of theoretical models of hand preference in nonhuman primates presented by MacNeilageet al. (1987) and by Fagot and Vauclair (1991). We also discuss several methodological and statistical issues as they pertain to the assessment of hand preference in great apes and other primate species. Finally, we present a comparative framework for the study of hand preference, emphasizing the importance of studies with great apes in developing evolutionary models of hemispheric specialization.     

Ecological constraints on the grouping of wild orang-utans (Pongo pygmaeus) in the Gunung Leuser National Park,Sumatra, Indonesia

The orang-utan (Pongo pygmaeus)is an interesting subject on which to base an evaluation of the costs and benefits of social life in apes, since grouping in this heavy, arboreal frugivore is facultative. In the Ketambe area of Sumatra, Indonesia, the food sources of wild orang-utans display a clear seasonality. The two main food types— figs and other, nonfig, fruits— fulfill different functions. The huge fig trees meet the high caloric requirements of the ape and are therefore visited regularly throughout the year. Nonfig fruits are an additional food source but become a really important alternative when figs are in short supply. Since fig trees are relatively rare, it is only in the nonfig fruiting season that food is relatively abundant. Two types of orang-utan groupings could be distinguished. During lean periods, groups formed in the few productive fig trees available can be explained as forced aggregations taking place in spite of centrifugal forces caused by competition. Only when a temporary surfeit of food slackens these centrifugal forces (i.e., during the fruit season) does the tendency to form spontaneous social groups (the second type of grouping) reveal itself. It is suggested that the development of social skills is an important aspect of grouping in adolescent orang-utans. For the adult male, safeguarding his reproductive success by protecting females against sexually aggressive subadult males is probably the only reason for being in groups.