Handedness in the common marmoset (Callithrix jacchus)

For about 20 months the development of hand preferences in 21 experimentally naive common marmosets (Callithrix jacchus) was examined in 15 different tests. Test preferences were compared with their spontaneous behavior preferences in such contexts as feeding, grooming, play, and others. In the spontaneous use of the hands, only eight animals showed a significant lateral preference (2 left-handed, 6 right-handed). During the test period, however, the number of handed marmosets increased to 19 (5 left-handed, 14 right-handed). Most of the animals fluctuated considerably in their preference levels, a situation which led to a remarkable test response inconsistency of handedness. When the test situation was changed, complete reversals of handedness were more frequent than weakening or strengthening of a particular preference. The animals' emotions during the test session and environmental variables affected handedness significantly. None of the tested marmosets showed an increase of hand preference from the first to the last test. Our results indicate that Callithrix is ambidextrous rather than handed.     

Infant cradling in a captive mother gorilla

The purpose of the study presented here was to investigate the handedness and cradling preferences of a mother gorilla (Gorilla gorilla) from the Metro Toronto Zoo. The study also examined preferences for handedness for each member of the captive group. Observational data were collected using scan sampling at 60‐sec intervals. Handedness was determined with a coordinated bimanual tube test using peanut butter spread on the interior of a PVC tube. Our findings were largely consistent with the literature on laterality in African apes by documenting a left‐side cradling bias for one apparently ambidextrous captive gorilla mother. This bias was associated with a left head positioning preference by her infant. Although based on a single mother/infant pairing, this study indicates that cradling bias is not always determined by maternal handedness. Zoo Biol 27:420–426, 2008. © 2008 Wiley‐Liss, Inc.     

Genetic and environmental contributions to the expression of handedness in chimpanzees (Pan troglodytes)

Most humans are right‐handed and, like many behavioral traits, there is good evidence that genetic factors play a role in handedness. Many researchers have argued that non‐human animal limb or hand preferences are not under genetic control but instead are determined by random, non‐genetic factors. We used quantitative genetic analyses to estimate the genetic and environmental contributions to three measures of chimpanzee handedness. Results revealed significant population‐level handedness for two of the three measures—the tube task and manual gestures. Furthermore, significant additive genetic effects for the direction and strength of handedness were found for all three measures, with some modulation due to early social rearing experiences. These findings challenge historical and contemporary views of the mechanisms underlying handedness in non‐human animals.     

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.     

Right‐handed fossil humans

Fossil hominids often processed material held between their upper and lower teeth. Pulling with one hand and cutting with the other, they occasionally left impact cut marks on the lip (labial) surface of their incisors and canines. From these actions, it possible to determine the dominant hand used. The frequency of these oblique striations in an array of fossil hominins documents the typically modern pattern of 9 right‐ to 1 left‐hander. This ratio among living Homo sapiens differs from that among chimpanzees and bonobos and more distant primate relatives. Together, all studies of living people affirm that dominant right‐handedness is a uniquely modern human trait. The same pattern extends deep into our past. Thus far, the majority of inferred right‐handed fossils come from Europe, but a single maxilla from a Homo habilis, OH‐65, shows a predominance of right oblique scratches, thus extending right‐handedness into the early Pleistocene of Africa. Other studies show right‐handedness in more recent African, Chinese, and Levantine fossils, but the sample compiled for non‐European fossil specimens remains small. Fossil specimens from Sima del los Huesos and a variety of European Neandertal sites are predominately right‐handed. We argue the 9:1 handedness ratio in Neandertals and the earlier inhabitants of Europe constitutes evidence for a modern pattern of handedness well before the appearance of modern Homo sapiens.     

Actigraphic Investigations On The Activity‐Rest Behavior Of Right‐ and Left‐Handed Students

The aim of this study was to explore differences between left‐and right‐handed subjects in sleep duration. Sleep and activity patterns were continuously registered for 12 days using actometers on 20 left‐handed and 20 right‐handed medical students in Berlin. Handedness was determined by a modified version of the Edinburgh handedness inventory. Each participant wore one actometer on each wrist. Actiwatch® Sleep Analysis Software (CNT, UK) was used to evaluate the data, and statistical calculations were performed with a non‐parametric variance analysis. A significant difference in mean sleep duration between left‐handers (7.9 h) and right‐handers (7.3 h) was determined (p=0.025 for measurement made on the dominant hand and p=0.013 for ones made on the non‐dominant hand). In contrast, the maximal phase of daily activity (acrophase) did not show any difference between the two groups. The difference in sleep duration might be caused by either the greater effort required for left‐handers to cope in a right‐handed world or by structural brain differences.     

Handedness preference and switching of peptide helices. Part I: Helices based on protein amino acids

In this article, we review the relevant results obtained during almost 60 years of research on a specific aspect of stereochemistry, namely handedness preference and switches between right‐handed and left‐handed helical peptide structures generated by protein amino acids or appropriately designed, side‐chain modified analogs. In particular, we present and discuss here experimental and theoretical data on three categories of those screw‐sense issues: (i) right‐handed/left‐handed α‐helix transitions underwent by peptides rich in Asp, specific Asp β‐esters, and Asn; (ii) comparison of the preferred conformations adopted by helical host–guest peptide series, each characterized by an amino acid residue (e.g. Ile or its diastereomer aIle) endowed with two chiral centers in its chemical structure; and (iii) right‐handed (type I)/left‐handed (type II) poly‐(Pro)_n helix transitions monitored for peptides rich in Pro itself or its analogs with a pyrrolidine ring substitution, particularly at the biologically important position 4. The unique modular and chiral properties of peptides, combined with their relatively easy synthesis, the chance to shape them into the desired conformation, and the enormous chemical diversity of their coded and non‐coded α‐amino acid building blocks, offer a huge opportunity to structural chemists for applications to bioscience and nanoscience problems. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Termite fishing laterality in the fongoli savanna chimpanzees (Pan troglodytes verus): Further evidence of a left hand preference

Whether nonhuman primates show population‐level handedness is a topic of much scientific debate. A previous study of handedness for termite fishing reported population‐level left handedness in the chimpanzees from Gombe National Park, Tanzania. In the current study, we examined whether similar hand preferences were evident in a savanna‐dwelling chimpanzee population with regards to termite fishing. Hand preference data were collected for 27 chimpanzees from February 2007 through July 2008 and November 2011 through January 2012 in southeastern Senegal. Overall, the Fongoli chimpanzees demonstrate a trend toward population‐level handedness, though the results did not reach conventional levels of statistical significance likely due to the limited sample size. Fongoli chimpanzees showed the same pattern of left hand preference as reported at Gombe and the two populations did not differ significantly. When the data were combined across all studies, wild chimpanzees showed a population‐level left hand preference for termite fishing. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Hand preference study in marmosets (Callithrix jacchus) using food reaching tests

Hand preference has been investigated in New World primates but the data obtained thus far are controversial. In this study we investigated hand preference in common marmosets,Callithrix jacchus, during the execution of a reaching for food task. We used 46 adult common marmoset males (n=27) and females (n=19) from the Universidade of Rio Grande do Norte colony, both wild and captive-born. To test the hand preference we used a device measuring 10 cm², with a central hole 1 cm in diameter, to force the animal to use only one hand to reach for food on a food dish located underneath. Each animal was tested 5 times and had to make a maximum of 20 successful attempts per session. A total of 100 successful attempts per animal and 4,600 successful attempts for all animals were recorded during the experiment. Latency and duration of the sessions were measured and we found preference for the use of one of the hands in common marmoset individuals, i.e. 45 of total of 46 animals used significantly more the right or the left hand when performing the task. However no bias at the population level was found. Females born in captivity presented an increase in the duration of latency for the first successful attempt and in the total duration of the test sessions. These findings might be indicating differences associated with a natural tendency for females to be more selective and to spend more time exploring alimentary sources. Additionally, captive-born females may have a constrain in developing cognitive abilities regarding foraging since they have food available during most part of the time.     

Black lemur (Lemur macaco) hand preference in food reaching

The present study assessed the hand preferences exhibited by 33 black lemurs during routine feeding. Individual animals displayed hand preferences that were consistent across observations separated by as much as seven months. Within this population, 20 were left hand preferent, 12 right preferent, and 1 was ambidextrous. Correlational analysis of age and percentage left hand use indicated an inverse relationship in which younger animals tended towards the preferential use of the left hand and older animals the preferential use of the right hand. Similar analysis found no relationship between either sex and hand preference or familial relationship and hand preference. The skewed distribution of age in this sample renders tentative conclusions regarding age-related variations in hand preference. It is suggested that if the hand preferences of the black lemur are not age-related, then this species may be characterized as having a bias towards the preferential use of the left hand for food reaching.     

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.     

On the handedness of Japanese monkeys

Forty-one monkeys living on the Koshima Island were tested for handedness by throwing a peanut 10 or 20 times toward each subject and recording which hand was used to pick it up. Handedness was judged at the 5% level of confidence. Animals showing no preference for the left or right hand after 20 trials were considered to be ambidextrous. The following distribution of handedness was found: left-handed, 17 (41%); right-handed, 8 (20%); ambidextrous, 16 (39%). These findings were compared with other studies on the handedness of Japanese monkeys. Handed monkeys outnumber the ambidextrous ones and the left-handed monkeys outnumber the right-handed ones. The characteristic distribution of handedness was shown to be irrespective of troop. By looking over the data from these different sources, the proportions of the left-handed, the ambidextrous, and the right-handed in Japanese monkeys were estimated at 39%, 33%, and 28% respectively. The method used in this study was compared withKawai's catching behavior and reasons for disagreement between judgments of handedness were discussed.     

Hand Preferences for a Haptic Task in Chimpanzees (Pan troglodytes)

We tested the hand preferences of 20 chimpanzees (Pan troglodytes) for a haptic task requiring individuals to search for grapes in an opaque bucket filled with water. We compared these data to the hand preferences displayed by the same chimpanzees during reaching and bimanual feeding tasks. The chimpanzees displayed no significant hand preference for the reaching or bimanual feeding tasks, but exhibited a right-hand preference while performing the haptic task. In contrast, New and Old World monkeys display left-hand preferences for similar tasks. We discuss the relevance of these findings for the evolution of handedness in primates.     

Hand preference in a captive island group of chimpanzees (Pan troglodytes)

Morphological cerebral asymmetries in chimpanzee brains, similar to those found in humans, in whom they are associated with speech and handedness, suggest the possibility of functional lateralization in the chimpanzee. This possibility was investigated by examining hand preferences in an island group of five chimpanzees on a series of unimanual and bimanual tasks that are diagnostic of human hand and cerebral dominance. Each subject was tested in a double compartment cage on three unimanual nonsequential, three unimanual sequential, and three bimanual coordination tasks. One of the three unimanual sequential tasks was a bar-press task that is analogous to the commonly used human finger-tapping task. For the unimanual tasks, exclusive of the bar-press, the chimpanzees showed a highly individualistic pattern of hand preference that did not change as a function of task complexity. On the bar-press task, four of five subjects produced higher rates with one hand compared to the other; however, relative hand performance on this task was unrelated to hand preference on the other unimanual tasks. For the group of subjects, performance rates did not differ between the left and right hands; however, a practice effect was observed for the right hand in all subjects. The bimanual tasks also revealed a complex pattern of individual handedness, with no trends apparent for the group as a whole. Consistent with previous findings, the results from these tests on this group of five chimpanzees suggest that cerebral morphological asymmetries in the chimpanzee are not associated with motor dominance as reflected in handedness.     

Bilateral asymmetry in bone measurements of the hand and lateral hand dominance

Two hundred thirty–five (235) normal male participants of the Baltimore Longitudinal Study were classified as right handed, left handed, and ambidextrous on the basis of their grip–strength performance. Their left and right hands were also radiographed and the measurements of the second metacarpal bones were evaluated on the basis of hand dominance. The results indicated that, as a rule, the right hand measurements are higher than those of the left hand, regardless of hand dominance. The bilateral differences in total width, length, total area and cortical area are significant among the right hand dominant and nonsignificant among the left hand dominant. Regardless off hand dominance the bilateral differences in medullary width are nonsignificant. These results suggest an inherent tendency of the right second metacarpal to have more bone than the left regardless of hand dominance. Differential stress due to hand dominance will increase the bilateral difference in the right handed and reduce it in the left handed.     

Hand preferences on unimanual and bimanual tasks in Tonkean macaques (Macaca tonkeana)

This is the first study to examine hand preferences in Tonkean macaques on a bimanual task. One of our objectives was to continue the move toward greater task standardization, in order to facilitate comparisons between species and studies on handedness. The main aim was to test and determine task robustness, by varying intra‐task complexity. To this end, we administered several different tasks to the subjects: two unimanual tasks (grasping task featuring items of different sizes) and three coordinated bimanual tasks (tube task involving different materials, weights, and diameters). Although we found no significant hand preference in either task at the group level, the macaques were more strongly lateralized for small items than for large ones in the unimanual grasping task. Moreover, the absence of a correlation between these two versions of the unimanual task confirmed the weakness of this grasping task for assessing handedness. Regarding the bimanual tube task, no difference was found between the three versions in either the direction or the strength of hand preference. Moreover, the highly correlated hand preferences between these three versions suggest that the tube task provides a more robust means of measuring manual preferences. Am J Phys Anthropol 152:315–321, 2013. © 2013 Wiley Periodicals, Inc.     

Alpha helical crossovers favor right‐handed supersecondary structures by kinetic trapping: The phone cord effect in protein folding

The remarkable predominance of right‐handedness in beta‐alpha‐beta helical crossovers has been previously explained in terms of thermodynamic stability and kinetic accessibility, but a different kinetic trapping mechanism may also play a role. If the beta‐sheet contacts are made before the crossover helix is fully formed, and if the backbone angles of the folding helix follows the energetic pathway of least resistance, then the helix would impart a torque on the ends of the two strands. Such a torque would tear apart a left‐handed conformation but hold together a right‐handed one. Right‐handed helical crossovers predominate even in all‐alpha proteins, where previous explanations based on the preferred twist of the beta sheet do not apply. Using simple molecular simulations, we can reproduce the right‐handed preference in beta‐alpha‐beta units, without imposing specific beta‐strand geometry. The new kinetic trapping mechanism is dubbed the “phone cord effect” because it is reminiscent of the way a helical phone cord forms superhelices to relieve torsional stress. Kinetic trapping explains the presence of a right‐handed superhelical preference in alpha helical crossovers and provides a possible folding mechanism for knotted proteins.     

A study of correlates of hand preferences in squirrel monkeys (Saimiri sciureus)

The purpose of this study was to test the influence of sex, age, social rank, matriline membership, posture, and visual and tactual motor control on manual preferences inSaimiri sciureus. A well-established social group of 12 squirrel monkeys, aged 2 to 14 yrs and consisting of two matrilines with social rank known for each animal, was presented with four different food-reaching tasks and assessed for hand preferences with a minimum of 100 reaches per animal. Frequency of occurrence of hand preferences at the group level and degree of hand preferences at the individual level depended on posture and on whether the reaching act took place under visual or tactual guidance. Sex, age, social rank, and matriline membership were not found to determine frequency of occurrence, direction or degree of hand preferences with the exception of one task in which a significant negative correlation between the degree of hand preference and age was found. Nine out of 12 monkeys showed task-dependent changes in the hand they used preferentially while only three animals preferred the same hand in all four tasks. Significant preferences for the use of right or left hand on a given task were distributed almost equally between individuals. Thus, the results of this study suggest task-specific demands like posture and/or whether reaching was visually or tactually guided to be the major correlates of hand preferences in food-reaching tasks in squirrel monkeys.     

Brief communication: Captive gorillas are right‐handed for bimanual feeding

Predominance of right‐handedness has historically been considered as a hallmark of human evolution. Whether nonhuman primates exhibit population‐level manual bias remains a controversial topic. Here, we investigated the hypothesis that bimanual coordinated activities may be a key‐behavior in our ancestors for the emergence and evolution of human population‐level right‐handedness. To this end, we collected data on hand preferences in 35 captive gorillas (Gorilla gorilla) during simple unimanual reaching and for bimanual coordinated feeding. Unimanual reaching consisted of grasping food on the ground, while bimanual feeding consisted of using one hand for holding a food and processing the food item by the opposite hand. No population‐level manual bias was found for unimanual actions but, in contrast, gorillas exhibited a significant population‐level right‐handedness for the bimanual actions. Moreover, the degree of right‐handedness for bimanual feeding exceeds any other known reports of hand use in primates, suggesting that lateralization for bimanual feeding is robust in captive gorillas. The collective evidence is discussed in the context of potential continuity of handedness between human and nonhuman primates. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Factor Analysis of Multiple Measures of Hand Use in Captive Chimpanzees: An Alternative Approach to the Assessment of Handedness in Nonhuman Primates

We tested whether chimpanzee handedness could be characterized as either unidimensional or multidimensional when considered across multiple measures of hand use. We determined for each of 6 different tasks in a sample of 105 captive chimpanzees hand preferences, and subjected the individual hand preference scores to a factor analysis. Five of the 6 tasks loaded on two separate factors that accounted for 54% of the variance. To assess population-level handedness, we calculated handedness indices for the loadings on each factor, for the item loadings across all factors, and for all tasks including ones that did not load on any factor. There is significant population-level right handedness for all 4 indices, which suggests that chimpanzee handedness is multidimensional and not task specific.