Early signs of language in cross-fostered chimpanzees

In cross-fostering the young of one species are reared by adults of another, as in the classical ethological studies of imprinting and song-learning. In our laboratory, infant chimpanzees were reared under human conditions that included two-way communication in American Sign Language (ASL) the gestural language of the deaf in North America. Here we describe the cross-fostering conditions of this laboratory and the contrast with operant conditioning. We also review the uses and the shapes of the signs in the vocabularies of five cross-fostered chimpanzees, tests demonstrating that the cross-fostered chimpanzees could use signs of ASL to communicate conceptual information to human observers whose only source of information was the signs of the chimpanzees, early development of inflections that resemble the early inflections of deaf human children, evidence based on errors and on inflections for duality of patterning, the continued use of sign language among the chimpanzees even when deprived of human input and the acquisition of signs by the infant Loulis from the cross-fostered chimpanzees.     

Signs of intelligence in cross-fostered chimpanzees

In cross-fostering, the young of one species are reared by adults of another, as in the classical ethological studies of imprinting and song-learning. In our laboratory, infant chimpanzees were reared under human conditions that included two-way communication in American Sign Language (A.S.L.), the gestural language of the deaf in North America. A large body of evidence from five chimpanzees demonstrated stage by stage replication of basic aspects of the acquisition of speech and signs by hearing and deaf children. Here we review evidence that, under double-blind conditions: (i) the chimpanzees communicated information in A.S.L. to human observers; (ii) independent human observers agreed in their identification of the chimpanzee signs, (iii) the chimpanzees could use the signs to refer to natural language categories: DOG for any dog, FLOWER for any flower, SHOE for any shoe.     

The role of cross-fostering in sign language studies of chimpanzees

In cross-fostering, the young of one species are reared by adults of another. In our cross-fostering laboratory, two-way communication by means of American Sign Language (ASL) brought the rearing conditions for chimpanzees much closer to those of human children than was possible in earlier studies. At the same time, ASL provided a means by which chimpanzees could express their intelligence in ways that permit closer comparisons with human children. Cross-fostered chimpanzees can communicate with human observers whose only source of information is the American Sign Language (ASL) signs of the chimpanzees. In order to show that the chimpanzees could name natural language categories — that the sign DOG could refer to any dog, FLOWER to any flower, SHOE to any shoe — each test trial was a first trial in that tests slides were presented only once. Analysis of errors showed that two aspects of the signs, gestural form and conceptual category, governed the distribution of errors. Like human adults and human children who sign, the chimpanzees modulated their signs in meaningful ways. Observations in field notes, video tape records, and systematic experiments illustrate how these modulations were related to the verbal and nonverbal, context and how they made signs more visible, more versatile, and more informative.     

Functional analysis of chimpanzee (Pan troglodytes) private signing

The chimpanzee's use of American Sign Language (ASL) to communicate with humans and with each other has been empirically demonstrated in several reports, but this is the first research to experimentally examine their use of sign language in a nonsocial fashion: private signing. This experiment examined the private signing behavior of five signing chimpanzees, using a remote videotaping technique with no human present. It was found that all five chimpanzees signed to themselves for a total of 368 instances. These instances of private signing were classified into nine different functional categories as has been done in the analysis of private speech and signing in hearing and deaf human children. Similar to humans, a few of the categories accounted for the majority of the instances of private signing. These findings empirically demonstrate a behavior similar to private speech and signing in humans.     

Chimpanzee to chimpanzee American Sign Language

The current study examined how five chimpanzees combined the signs of American Sign Language with their nonverbal communication during high arousal interactions. Thirty-five hours of videotape were analyzed for the presence of high arousal interactions. Similar to deaf children, the chimpanzees signed to one another during high arousal interactions, and they emphatically modulated their signs by signing more vigorously, enlarging the sign’s movement, prolonging the sign, reiterating the sign, or by using a two-handed version of a sign regularly signed with one hand. The majority of the chimpanzees’ sign utterances were contextually consistent. The chimpanzees’ sign utterances were scored as contextually consistent if they were used in previous high arousal interactions which were not part of the current study. Individual chimpanzee differences in signing frequency, emphatic modulation, and recipient allocation were found. Similar to humans, the chimpanzees’ verbal communication is a robust phenomena which continues to occur even during high arousal interactions.     

Development of phrases in the early utterances of children and cross-fostered chimpanzees

Project Washoe and its sequel with Moja, Pili, Tafu, and Dar, simulated with infant chimpanzees the conditions in which the language of human children develops gradually and-piecemeal into the language of human parents. This article traces patterns of growth and development in the early utterances of children and chimpanzees. The evidence for continuous processes and variables contradicts the yes-no, either-or Aristotelian logic of philosophical linguistics that has prevailed for so long. What the children and chimpanzees actually say supports, instead, a view of common laws and continuity that is much more compatible with modern natural science.     

Ethological study of early language

Sign language studies of cross-fostered chimpanzees measure the effect of special rearing conditions on the development of very young chimpanzees. Cross-fostered chimpanzees, like human children, develop gradually in a process that takes many years. Here we discuss details of the procedure, the overlap between human and chimpanzee infants in the contents of the first 50-item vocabularies, and the ways in which the signs of the chimpanzees exhibit the fuzziness of natural language categories. We also compare the cross-fostering approach with more traditional modular approaches to the study of language-like behavior in nonhuman animals. Project Washoe was originally supported by grants MH-12154 from the National Institute of Mental Health and GB-7432 from the National Science Foundation. We gratefully acknowledge this support and the support that later sign language studies of chimpanzees have received since then from NIH, NSF, the National Geographic Society, the Grant Foundation, the Spencer Foundation, the University of Nevada, and the UNR Foundation.     

The ontogeny of human prosociality: behavioral experiments with children aged 3 to 8

Humans regularly engage in prosocial behavior that differs strikingly from that of even our closest living relatives, the chimpanzees (Pan troglodytes). In laboratory settings, chimpanzees are indifferent when given the opportunity to deliver valued rewards to conspecifics, while even very young human children have repeatedly been shown to behave prosocially. Although this broadly suggests that prosocial behavior in chimpanzees differs from that of young human children, the methods used in prior work with children have also differed from the methods used in studies of chimpanzees in potentially crucial ways. Here we test 92 pairs of 3–8-year-old children from urban American (Los Angeles, CA, USA) schools in a face-to-face task that closely parallels tasks used previously with chimpanzees. We found that children were more prosocial than chimpanzees have previously been in similar tasks, and our results suggest that this was driven more by a desire to provide benefits to others than a preference for egalitarian outcomes. We did not find consistent evidence that older children were more prosocial than younger children, implying that younger children behaved more prosocially in the current study than in previous studies in which participants were fully anonymous. These findings strongly suggest that humans are more prosocial than chimpanzees from an early age and that anonymity influences children's prosocial behavior, particularly at the youngest ages.     

Peer separation in infant chimpanzees,a pilot study

Seven nursery reared chimpanzees (Pan troglodytes), 7.5 to 10.5 months of age, were studied to determine the effects of a short period of separation from their peers on behavior and heart rate. The chimpanzees were separated from their mothers at birth, and reared in the nursery in a group living environment. The experiment encompassed a 13-day period, including 4 days of normative baseline, 5 days during which three of the infants were separated and housed in isolation while the other four controls remained together, and 4 days in which all of the animals were reunited. Six quantified behavioral observations and five heart rate measurements were obtained daily. Following separation, the isolated infants were behaviorally agitated, and exhibited increases in vocalizations, rocking and self-clasp behaviors, as well as changes in facial expression including cry face, whimper face and pout face. Time spent locomoting decreased in all seven animals during the separation period. Agitated behavior in the separated and isolated infants alternated with stationary withdrawn behavior. Individual differences were prominent. Heart rate was notable by the generally poorly developed circadian rhythmicity throughout the 13 day period; significant HR changes did not appear otherwise associated with separation. Day three of separation appeared to represent a point of transition with stereotyped motor behaviors developing in the three isolated infants and in one control infant.     

Variations in the arbitrariness of ASL: an assessment of the symbolicity of simian signs

This paper summarizes and applies a continuum of «arbitrariness» or «symbolicity» composed of symptoms, rituals and symbols to the results of research in which American Sign Language (ASL) was used as the method of «language» training. Additionally, an expansion of the symbolicity continuum to include a continuum of «abstractness» with the «conceptual symbol» anchoring the most arbitrary end of the continuum was advanced. The results of the comparison provide additional support for the claim that apes are capable of learning and using symbolic signs. However, only a small number of those symbolic signs could be considered «conceptual symbols».     

Rehabilitation of research chimpanzees: stress and coping after long-term isolation

We report on the permanent retirement of chimpanzees from biomedical research and on resocialization after long-term social isolation. Our aim was to investigate to what extent behavioral and endocrine measures of stress in deprived laboratory chimpanzees can be improved by a more species-typical social life style. Personality in terms of novelty responses, social dominance after resocialization and hormonal stress susceptibility were affected by the onset of maternal separation of infant chimpanzees and duration of deprivation. Chimpanzees, who were separated from their mothers at a younger age and kept in isolation for more years appeared to be more timid personalities, less socially active, less dominant and more susceptible to stress, as compared to chimpanzees with a less severe deprivation history. However, permanent retirement from biomedical research in combination with therapeutic resocialization maximizing chimpanzees' situation control resulted in reduced fecal cortisol metabolite levels. Our results indicate that chimpanzees can recover from severe social deprivation, and may experience resocialization as less stressful than solitary housing.     

When Learners Surpass Their Models: Mathematical Modeling of Learning from an Inconsistent Source

It has been reported in the literature that both adults and children can, to a different degree, modify and regularize the often-inconsistent linguistic input they receive. We present a new algorithm to model and investigate the learning process of a learner mastering a set of (grammatical or lexical) forms from an inconsistent source. The algorithm is related to reinforcement learning and drift–diffusion models of decision making, and possesses several psychologically relevant properties such as fidelity, robustness, discounting, and computational simplicity. It demonstrates how a learner can successfully learn from or even surpass its imperfect source. We use the data collected by Singleton and Newport (Cognit Psychol 49(4):370–407, 2004) on the performance of a 7-year-boy Simon, who mastered the American Sign Language (ASL) by learning it from his parents, both of whom were imperfect speakers of ASL. We show that the algorithm possesses a frequency boosting property, whereby the frequency of the most common form of the source is increased by the learner. We also explain several key features of Simon’s ASL.     

Comparison of Development and Life History in Pan and Cebus

We examined growth and development in capuchins and chimpanzees in relation to weaning, onset of reproduction, and reproductive life span. Striking differences are evident in neurobehavioral status at birth (more mature in capuchins), the relative duration of infancy (longer in chimpanzees), and the proportional weight of the infant at the time of weaning (greater in capuchins). Although capuchins and chimpanzees spend a similar proportion of life in a weaned but reproductively immature state, chimpanzees spend so much more of their lives as nursing infants that reproductive output per individual is much lower than in capuchins. Discussion centers around tolerated transfers of food (food-sharing) as a potential adaptation to limited foraging success by immature foragers. Perhaps food transfers from adult to infant, which is a more prominent feature of behavior in chimpanzees than in capuchins in natural environments, allow a very small weanling chimpanzee to survive.     

Differential prefrontal white matter development in chimpanzees and humans

A comparison of developmental patterns of white matter (WM) within the prefrontal region between humans and nonhuman primates is key to understanding human brain evolution. WM mediates complex cognitive processes and has reciprocal connections with posterior processing regions [1, 2]. Although the developmental pattern of prefrontal WM in macaques differs markedly from that in humans [3], this has not been explored in our closest evolutionary relative, the chimpanzee. The present longitudinal study of magnetic resonance imaging scans demonstrated that the prefrontal WM volume in chimpanzees was immature and had not reached the adult value during prepuberty, as observed in humans but not in macaques. However, the rate of prefrontal WM volume increase during infancy was slower in chimpanzees than in humans. These results suggest that a less mature and more protracted elaboration of neuronal connections in the prefrontal portion of the developing brain existed in the last common ancestor of chimpanzees and humans, and that this served to enhance the impact of postnatal experiences on neuronal connectivity. Furthermore, the rapid development of the human prefrontal WM during infancy may help the development of complex social interactions, as well as the acquisition of experience-dependent knowledge and skills to shape neuronal connectivity.     

The price of play: self-organized infant mortality cycles in chimpanzees

Chimpanzees have been used extensively as a model system for laboratory research on infectious diseases. Ironically, we know next to nothing about disease dynamics in wild chimpanzee populations. Here, we analyze long-term demographic and behavioral data from two habituated chimpanzee communities in Ta? National Park, C?te d'Ivoire, where previous work has shown respiratory pathogens to be an important source of infant mortality. In this paper we trace the effect of social connectivity on infant mortality dynamics. We focus on social play which, as the primary context of contact between young chimpanzees, may serve as a key venue for pathogen transmission. Infant abundance and mortality rates at Ta? cycled regularly and in a way that was not well explained in terms of environmental forcing. Rather, infant mortality cycles appeared to self-organize in response to the ontogeny of social play. Each cycle started when the death of multiple infants in an outbreak synchronized the reproductive cycles of their mothers. A pulse of births predictably arrived about twelve months later, with social connectivity increasing over the following two years as the large birth cohort approached the peak of social play. The high social connectivity at this play peak then appeared to facilitate further outbreaks. Our results provide the first evidence that social play has a strong role in determining chimpanzee disease transmission risk and the first record of chimpanzee disease cycles similar to those seen in human children. They also lend more support to the view that infectious diseases are a major threat to the survival of remaining chimpanzee populations.     

Maternal caregiving and DNA methylation in human infants and children: Systematic review

The integration of behavioral epigenetics' principles (eg, DNA methylation) into the study of human infants' development has mainly focused on the effects of early adverse exposures, paying less attention to protective caregiving experiences. The present review focused on DNA methylation linked to variations in maternal behavior in human infants and children. Literature search occurred on three databases (PubMed, Scopus and Web of Science) and 11 records were selected. Key variables were abstracted from each article including: sample size and characteristics, time and type of maternal caregiving behavior exposure, time and locus of methylation biomarker, presence/absence, time and type of adverse exposure. Six out of eleven records documented the predictive effect of maternal caregiving on DNA methylation, whereas the remaining five reported on the role of maternal behavior as an influencing factor of the adversity‐to‐methylation link. Consistent with evidence from the animal model, the quality of maternal caregiving in humans (a) might be associated with variations in DNA methylation status of specific genes involved in socio‐emotional development and (b) might partially buffer the association between early adversities and epigenetic variations in infants and children. Current evidence suggests that the quality of maternal caregiving can contribute to behavioral development trajectories of human infants and children at least partially through epigenetic regulation. Open questions and methodological aspects are discussed to guide future human developmental research in behavioral epigenetics.     

Majority-biased transmission in chimpanzees and human children, but not orangutans

Cultural transmission is a key component of human evolution. Two of humans' closest living relatives, chimpanzees and orangutans, have also been argued to transmit behavioral traditions across generations culturally [1-3], but how much the process might resemble the human process is still in large part unknown. One key phenomenon of human cultural transmission is majority-biased transmission: the increased likelihood for learners to end up not with the most frequent behavior but rather with the behavior demonstrated by most individuals. Here we show that chimpanzees and human children as young as 2 years of age, but not orangutans, are more likely to copy an action performed by three individuals, once each, than an action performed by one individual three times. The tendency to acquire the behaviors of the majority has been posited as key to the transmission of relatively safe, reliable, and productive behavioral strategies [4-7] but has not previously been demonstrated in primates.     

Genetic and Environmental Factors Associated with Laboratory Rearing Affect Survival and Assortative Mating but Not Overall Mating Success in Anopheles gambiae Sensu Stricto

Anopheles gambiae sensu stricto, the main vector of malaria in Africa, is characterized by its vast geographical range and complex population structure. Assortative mating amongst the reproductively isolated cryptic forms that co-occur in many areas poses unique challenges for programs aiming to decrease malaria incidence via the release of sterile or genetically-modified mosquitoes. Importantly, whether laboratory-rearing affects the ability of An. gambiae individuals of a given cryptic taxa to successfully mate with individuals of their own form in field conditions is still unknown and yet crucial for mosquito-releases. Here, the independent effects of genetic and environmental factors associated with laboratory rearing on male and female survival, mating success and assortative mating were evaluated in the Mopti form of An. gambiae over 2010 and 2011. In semi-field enclosures experiments and despite strong variation between years, the overall survival and mating success of male and female progeny from a laboratory strain was not found to be significantly lower than those of the progeny of field females from the same population. Adult progeny from field-caught females reared at the larval stage in the laboratory and from laboratory females reared outdoors exhibited a significant decrease in survival but not in mating success. Importantly, laboratory individuals reared as larvae indoors were unable to mate assortatively as adults, whilst field progeny reared either outdoors or in the laboratory, as well as laboratory progeny reared outdoors all mated significantly assortatively. These results highlight the importance of genetic and environment interactions for the development of An. gambiae''s full mating behavioral repertoire and the challenges this creates for mosquito rearing and release-based control strategies.     

Fingerspelling as a Novel Gateway into Reading Fluency in Deaf Bilinguals

Studies have shown that American Sign Language (ASL) fluency has a positive impact on deaf individuals’ English reading, but the cognitive and cross-linguistic mechanisms permitting the mapping of a visual-manual language onto a sound-based language have yet to be elucidated. Fingerspelling, which represents English orthography with 26 distinct hand configurations, is an integral part of ASL and has been suggested to provide deaf bilinguals with important cross-linguistic links between sign language and orthography. Using a hierarchical multiple regression analysis, this study examined the relationship of age of ASL exposure, ASL fluency, and fingerspelling skill on reading fluency in deaf college-age bilinguals. After controlling for ASL fluency, fingerspelling skill significantly predicted reading fluency, revealing for the first-time that fingerspelling, above and beyond ASL skills, contributes to reading fluency in deaf bilinguals. We suggest that both fingerspelling—in the visual-manual modality—and reading—in the visual-orthographic modality—are mutually facilitating because they share common underlying cognitive capacities of word decoding accuracy and automaticity of word recognition. The findings provide support for the hypothesis that the development of English reading proficiency may be facilitated through strengthening of the relationship among fingerspelling, sign language, and orthographic decoding en route to reading mastery, and may also reveal optimal approaches for reading instruction for deaf and hard of hearing children.     

Infant mortality in mother-reared captive chimpanzees at Taronga Zoo,Sydney

Infant mortality in mother-reared chimpanzees was examined from the records of Taronga Zoo, Sydney, Australia. Sex-specific mortality probabilities were calculated using standard demographic techniques. Male mortality was found to be considerably higher than female mortality. Using the same techniques, changes in infant mortality over time were calculated, with particular reference to changes that had occurred since the chimpanzees were transferred to a new open air enclosure in 1980. Mortality was found to have decreased dramatically since the move to the new enclosure, but the observed decline was exaggerated by the very high proportion of female infants. The main causes of infant death as ascertained from the zoo records were pneumonia and trauma. In addition, undetermined causes in the first day of life were numerous. An examination of the contexts of infanticide in wild and captive chimpanzees revealed slight differences, but factors such as aggression towards unfamiliar individuals and redirected aggression were common to both. Cannibalism in the zoo has so far been limited to the bodies of stillborn infants.