The evolution and biological correlates of hand preferences in anthropoid primates

The evolution of human right-handedness has been intensively debated for decades. Manual lateralization patterns in non-human primates have the potential to elucidate evolutionary determinants of human handedness. However, restricted species samples and inconsistent methodologies are limiting comparative phylogenetic studies. By combining original data with published literature reports, we assembled data on hand preferences for standardized object manipulation in 1,806 individuals from 38 species of anthropoid primates, including monkeys, apes, and humans. Based on that, we employ quantitative phylogenetic methods to test prevalent hypotheses on the roles of ecology, brain size and tool use in primate handedness evolution. We confirm that human right-handedness represents an unparalleled extreme among anthropoids and found taxa displaying significant population-level handedness to be notably rare. Species-level direction of manual lateralization was largely uniform among non-human primates and neither correlated with phylogeny nor with any of the selected biological predictors. In contrast, we recovered highly variable patterns of hand preference strength, which show signatures of both ecology and phylogeny. In particular, terrestrial primates tend to display weaker hand preferences than arboreal species. These results challenge popular ideas on primate handedness evolution, especially the postural origins hypothesis. Furthermore, they point to a potential adaptive benefit of disparate lateralization strength in primates, a measure of hand preference that has often been overlooked in the past. Finally, our data show that human lateralization patterns do not align with trends found among other anthropoids, suggesting that unique selective pressures gave rise to the unusual hand preferences displayed by our species.

Differential Ageing of the Brain Hemispheres: Evidence from a Longitudinal Study of Hand Preferences in Common Marmosets

This paper is concerned with decreasing asymmetry of motor control in ageing. It discusses age-related changes in humans and reports a longitudinal study of hand preferences in common marmosets. An annual assessment of hand preference for holding food was recorded throughout the lifespan of 19 marmosets that lived for at least 9 years, and half of those lived for at least 11 years. Those with a left-hand preference showed a gradual reduction in the strength of their hand preference throughout adult life. No significant change in the strength of hand preference was found in right-handed marmosets. Hence, ageing has a specific effect on motor control by the right hemisphere.

Maternal cradling bias drives early handedness in infant monkeys: A longitudinal study of grasping lateralization in baboons

The most emblematic behavioral manifestation of human brain asymmetries is handedness. While the precise mechanisms behind the development of handedness are still widely debated, empirical evidences highlight that besides genetic factors, environmental factors may play a crucial role. As one of these factors, maternal cradling behavior may play a key role in the emergence of early handedness in the offspring. In the present study we followed 41 olive baboon (Papio anubis) infants living in different social groups with their mother for which direction (e.g., left- or right-arm) and degree of maternal cradling-side bias were available from our previous published study. We assessed hand preferences for an unimanual grasping task at 3 developmental stages: (1) 0-4, (2) 4-6 and (3) 9-10 months of age. We found that individual hand preferences for grasping exist as soon as the first months of age, with a population-level left-handedness predominance, being stable until 6 months; to wit the period during which juveniles are mainly carried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed later in the development, once juveniles are no longer carried (i.e., from 9 to 10 months of age), are less consistent with the earlier developmental stages and no longer dependent from the maternal cradling bias. Our findings suggest that the ontogenetic dynamics of the infant’s hand preference and its changes might ultimately rely on the degree of infant dependence from the mother across development.Research HighlightsEarly postnatal individual hand preferences are detected for unimanual food grasping within the first four months of age.Earliest measures of infant hand preference are positively correlated with measures of maternal cradling lateralization.Hand preferences assessed later in the development, from 9 to 10 months of age are less consistent with the earlier developmental stages and independent from maternal cradling bias.

Dominant Hand Usage in Racket Sports and Detection of the Injured Regions

The aim of this study is to examine dominant hand usage and detect the injury regions in racket sports. A total of 98 athletes, of which 37 (37.8%) are female, 61 (62.2%) are male, studying at 11 different universities and attending competitions with schools teams with an average age of 21.11±1.66, height of 1.71±0.08 cm, weight of 64.92±10.85 kg, and BMI of 22.00±2.41(kg/m2) have participated in the study. When it comes to the distribution of the athletes by branches, the sample consists of 22 table tennis players, 24 badminton players, 25 tennis players and 27 squash players. The "Edinburgh Inventory Hand Preference Survey" was used as a data collection tool to determine the hand preferences of the athletes. In the determination of sports injuries suffered by athletes, the Cornell Musculoskeletal Discomfort Questionnaire was administered. There are significant differences between the lefty and righty athletes in terms of injuries in the left shoulder, left wrist and right lower leg regions when the injury regions in racket sports are compared by hand preferences (p<0.05). It is seen that the injuries that occur in right forearm, left wrist and the right upper leg regions of the athletes of racket sports differ according to branches (p<0.05). When the injury regions are examined according to hand preferences, it is seen that the injuries in the left shoulder, left wrist and lower right leg regions occur more in lefty athletes in comparison to righty athletes. When the relationship between the injury region regions and sports branches is examined, it can be argued that table tennis players suffer more frequent injuries in the left wrist compared to the players of other branches.

Captive gibbons (Hylobatidae) use different referential cues in an object-choice task: insights into lesser ape cognition and manual laterality

Background Utilization of visual referential cues by non-human primates is a subject of constant scientific interest. However, only few primate species, mostly great apes, have been studied thoroughly in that regard, rendering the understanding of phylogenetic influences on the underlying cognitive patterns difficult. Methods We tested six species of captive gibbons in an object-choice task (n = 11) for their ability to interpret two different pointing gestures, a combination of body orientation and gaze direction as well as glancing as referential cues. Hand preferences were tested in the object-choice task and in a bimanual tube task (n = 18). Results We found positive responses to all signals except for the glancing cue at the individual as well as at the group level. The gibbons’ success rates partially exceed results reported for great apes in comparable tests and appear to be similarly influenced by prior exposure to human communicative cues. Hand preferences exhibited by the gibbons in the object-choice task as well as in a bimanual tube task suggest that crested gibbons (Nomascus sp.) are strongly lateralized at individual but not at population level for tasks involving object manipulation. Discussion Based on the available data, it can be assumed that the cognitive foundations to utilize different visual cues essential to human communication are conserved in extant hominoids and can be traced back at least to the common ancestor of great and lesser apes. However, future studies have to further investigate how the social environment of gibbons influences their ability to exploit referential signals. Gibbons’ manual laterality patterns appear to differ in several aspects from the situation found in great apes. While not extensive enough to allow for general conclusions about the evolution of hand preferences in gibbons or apes in general, our results add to the expanding knowledge on manual lateralization in the Hylobatidae.