Teat preference for suckling in common marmosets: relationship to side of being carried and hand preference

Mother and offspring lateralized social behavior across mammalian species

Findings on nonprimate mammals place the issue of mother-infant lateralized relations in a broader context, demonstrating that humans are one of many species showing this feature. The remarkable interspecies consistency in the direction of lateralization points to a continuity between lateralized mother-infant interactions in primates and nonprimate mammals and suggests ancient evolutionary roots of human cradling bias. The results from species which, in contrast to primates, have no direct involvement of forelimbs in mother-infant spatial interactions clearly support the perceptual origin of this type of lateralization. A right hemisphere advantage for social functions relevant to mother-infant interactions is the most probable background for the left-sided biases in the behavior of mothers and infants. Recent findings suggest the contribution of lateralized mother-infant interactions to biological fitness. Mother and infant both can gain advantage from keeping the other on the left side.

Captive gorillas' manual laterality: The impact of gestures, manipulators and interaction specificity

Relationships between humans' manual laterality in non-communicative and communicative functions are still poorly understood. Recently, studies showed that chimpanzees' manual laterality is influenced by functional, interactional and individual factors and their mutual intertwinement. However, what about manual laterality in species living in stable social groups? We tackled this question by studying three groups of captive gorillas (N=35) and analysed their most frequent manual signals: three manipulators and 16 gesture types. Our multifactorial investigation showed that conspecific-directed gestures were overall more right-lateralized than conspecific-directed manipulators. Furthermore, it revealed a difference between conspecific- and human-directed gestural laterality for signallers living in one of the study groups. Our results support the hypothesis that gestural laterality is a relevant marker of language left-brain specialisation. We suggest that components of communication and of manipulation (not only of an object but also of a conspecific) do not share the same lateralised cerebral system in some primate species.

Head-cocking as a form of exploration in the common marmoset and its development

Head-cocking of 15 infant marmosets (Callithrix jacchus) was scored from Day 1 to 60 of postnatal life, the growth period with overproduction of interneuronal synapses. Head-cocking was scored during four 30 min intervals daily, including angle of head-cocking and objects being fixated. Mean age of onset of head-cocking was Day 13 (+/-1.3) and frequency increased to a fixed rate by Day 24-29, at the time of maturation of the foveal representation in layer 6 of the visual cortex, thus lending further support to the importance of head-cocking to visual processing. The most common distance of objects fixated during head-cocking was up to .5 m. Angle of head-cocking increased with age, and some asymmetry of direction was noted. Fewer head-cocking events occurred in the morning than in the afternoon. We also scored anogenital licking of offspring. Head-cocking occurred at higher levels in marmosets receiving more anogenital licking. As this was associated positively with increased exploration, head-cocking may be regarded as an exploratory behavior.

Left Nipple Preferences in Infant Pan paniscus and P. troglodytes

We investigated laterality in nipple preference in 16 mother-infant dyads, 8 bonobos, and 8 chimpanzees via an event sampling procedure in infants 5-55 mo of age. Both bonobo and chimpanzee infants preferred the left nipple, and the results were stable over time. Maternal age, experience, and rearing history did not influence laterality in offspring nipple preferences. We discuss the results in the context of the role of early mother-infant interactions on the development of laterality in primates.

Comparative and familial analysis of handedness in great apes

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.

Left versus right nipple preference in free-ranging infant rhesus macaques (Macaca mulatta)

The examination of nonhuman primate (NHP) lateralized behaviors may provide insight into the evolution of hemispheric specialization. This study examined nipple preference in 64 infant macaques in order to consider the ontogeny of lateralized behavior. We used a focal animal sampling method to record nipple contact during 15, 30-min observation sessions collected across each infant's first year of life. Using a lateralized behavior index (LBI) we calculated individual and population preferences (LBI=(R-L)/(R+L); "R"=mean right nipple contact, "L"=mean left nipple contact). Strength of preference was calculated as the absolute value of this score. Infants exhibited no population preference for a particular nipple, but showed a significant strength of preference that developed after 48 hr. Interestingly, successive siblings preferred the nipple not used by the previous infant. These findings suggest that nipple preference is guided by external stimuli, and that nipple preference during infancy may not be a behavioral representation of hemispheric specialization.

Laterality in Maternal Cradling and Infant Positional Biases: Implications for the Development and Evolution of Hand Preferences in Nonhuman Primates

Left-sided maternal cradling has been widely reported in human populations. In this paper, I review the evidence of laterality in maternal cradling and infant positional biases in non-human primates. The review revealed some evidence of population-left sided cradling in great apes but little consistency in bias was found among Old and New World monkeys. Very little data have been reported in prosimians. I further describe how asymmetries in either maternal cradling or infant positional biases may explain individual and species differences in hand preference.

Development of hand preferences in marmosets (Callithrix jacchus) and effects of aging

The authors investigated the development of unimanual hand use and hand preferences during feeding in 15 marmosets (Callithrix jacchus), ages birth to 51-70 months. Bimanual hand use was common at 1-2 months, but by 5-8 months unimanual holding had developed and so had significant hand preferences. Half of the marmosets preferred to pick up and take food to the mouth with the left hand, and half preferred the right hand. Individuals maintained the same hand preference at all ages examined. Significant relationships were also found between the postures adopted during feeding and the direction of hand preferences displayed by juvenile marmosets. There was a positive correlation between increased suspension and increased left-hand preference, and a negative correlation between increased feeding in a tripedal posture and increased left-hand preference. These results are discussed in terms of motor development and hemispheric specialization.