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Evolutionary and developmental perspectives on accommodation: a comparative study of the early communicative gestures in humans and chimpanzees
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Advisor(s)
Abstract(s)
À medida que começamos a interagir no nosso meio social, torna-se fulcral aprendermos as
regras vigentes e as capacidades necessárias para prosperar, sendo a capacidade de ajustar a
forma como comunicamos uma capacidade chave. Ajustamos a nossa comunicação, consciente
ou subconscientemente, a diferentes níveis, podendo usar vários tipos de sinais ou ajustando
uma ampla variedade de características na forma como os produzimos. Mas se a capacidade de
acomodar é totalmente ou parcialmente derivada da linguagem levanta questões importantes
sobre quais elementos e quando é que estes são ajustados durante o nosso desenvolvimento
individual e na nossa trajetória evolutiva como espécie. Nesta tese, focamo-nos em gestos
devido à sua importância na ontogenia humana e na evolução da linguagem: as crianças
pequenas produzem gestos espontaneamente antes de começarem a usar a linguagem, e outros
grandes primatas usam um vasto repertório de gestos de forma flexível e intencional. Ao
compararmos as interações comunicativas em humanos e em chimpanzés, procuramos perceber
que características e capacidades comunicativas estariam presentes no nosso ancestral comum,
ajudando a elucidar as bases sociocognitivas da linguagem. Até ao momento, poucos estudos
incluem primatas humanos e não humanos, e por este motivo, fazer comparações implica
contrastarmos resultados de estudos diferentes que seguem abordagens distintas, tornando as
comparações desafiantes. Recorremos a uma metodologia semelhante para explorar como os
gestos são acomodados em duas comunidades de chimpanzés e quatro grupos de seres humanos
(crianças pequenas). Dentro deste quadro evolutivo, exploramos quer a capacidade de
acomodar a comunicação de uma perspetiva ampla, observando como os chimpanzés
comunicam em diferentes relacionamentos durante encontros e partidas, assim como em mais
detalhe exploramos os gestos das mães chimpanzés com os seus filhos e outros membros da
comunidade. Descobrimos que aspetos sociais dos relacionamentos, como parentesco e posição
hierárquica, influenciam a probabilidade de comunicação, e que o parentesco molda
características mais subtis dos gestos produzidos, como proeminência e padrões temporais.
Examinamos características detalhadas da comunicação gestual tanto em chimpanzés quanto
em humanos à luz do trabalho realizado na área da Comunicação Dirigida às Crianças (CDC).
As mães chimpanzés ajustaram a sua comunicação em relação aos indivíduos imaturos, mas de
maneiras que diferem dos ajustes que adultos humanos fazem na sua CDC: direcionaram
unidades gestuais mais curtas a indivíduos imaturos e usaram mais repetições quando
comunicaram com filhos mais velhos. Numa perspetiva de desenvolvimento, descobrimos que
a CDC surgiu precocemente antes da linguagem, com as crianças usando um vocabulário
gestual mais simples e fazendo gestos a um ritmo mais lento quando interagindo com colegas
mais novos. Mostramos que a capacidade de acomodar a nossa comunicação, inclusive em
relação a crianças pequenas, está presente na comunicação gestual de chimpanzés e crianças
pré-verbais, sugerindo que esta capacidade não é uma mera consequência da linguagem, mas
representa uma das capacidades fundamentais sobre as quais a linguagem é construída.
Partilhamos esta capacidade de acomodar a nossa comunicação com os chimpanzés, e é
provável que esta estivesse presente no nosso ancestral comum, mas diferentes pressões
seletivas podem ter moldado a expressão desta capacidade nas duas espécies.
ABSTRACT: As we begin to interact within our social environment, it becomes crucial to learn the rules and skills to thrive, and accommodating the way we communicate is a key ability. Humans adjust their communication, consciously or subconsciously, at different levels by using different types of signals or adjusting a wide range of features in how they produce them. But whether the ability to accommodate is fully or partially derived from language raises important questions about which elements of communication are adjusted, and when different adjustments emerge during our individual developmental and in our evolutionary trajectory as a species. In this thesis we focus on gestures because of its importance in human ontogeny and in language evolution: young children spontaneously gesture before they start using language, and other great apes use a vast repertoire of gestures flexibly and intentionally. Comparing communicative interactions in humans and in our modern relatives, chimpanzees, can provide insight into shared features, and the communicative abilities of our last common ancestor, helping to elucidate the socio-cognitive foundations of language. To date, very few studies include both human and nonhuman primates: consequently, making comparisons often relies on comparing findings from different studies. However, we show that human and nonhuman gestural research has followed different approaches, making comparisons challenging. We describe and employ a similar methodology to explore how gestures are accommodated in two chimpanzee communities and four groups of humans (toddlers). Within this evolutionary framework we explore both the ability to accommodate communication from a broad perspective by looking at how chimpanzees communicate across different relationships during greetings and leave-takings, and the in-depth exploration of the gestural communication of chimpanzee mothers with their infants and other community members. We found that social aspects of relationships, such as kinship and rank, influence the likelihood of communication, and that kinship shapes more subtle features of the gestures produced, such as prominence and temporal patterns. We examined nuanced features of gestural communication in both chimpanzees and humans in the light of work on Child-Directed Communication (CDC) in language. Chimpanzee mothers accommodated their communication towards young individuals, but in different ways to CDC accommodation in adult use of language: they used shorter gesture units towards immature individuals and used more repetition towards older offspring. Taking a developmental perspective, we found that CDC emerged early in ontogeny, before language, with toddlers using a simpler gestural vocabulary and gesturing at a slower pace towards younger peers. We show that the ability to accommodate our communication, including to young individuals, is present in gestural communication of chimpanzees and preverbal children, suggesting that this ability is not a mere consequence of language but instead represents one of the foundational capacities on which language use is built. We share this ability to accommodating our communication with chimpanzees, and it was likely present in our last common ancestor, but different selective pressures may have shaped the expression of this ability in the two species.
ABSTRACT: As we begin to interact within our social environment, it becomes crucial to learn the rules and skills to thrive, and accommodating the way we communicate is a key ability. Humans adjust their communication, consciously or subconsciously, at different levels by using different types of signals or adjusting a wide range of features in how they produce them. But whether the ability to accommodate is fully or partially derived from language raises important questions about which elements of communication are adjusted, and when different adjustments emerge during our individual developmental and in our evolutionary trajectory as a species. In this thesis we focus on gestures because of its importance in human ontogeny and in language evolution: young children spontaneously gesture before they start using language, and other great apes use a vast repertoire of gestures flexibly and intentionally. Comparing communicative interactions in humans and in our modern relatives, chimpanzees, can provide insight into shared features, and the communicative abilities of our last common ancestor, helping to elucidate the socio-cognitive foundations of language. To date, very few studies include both human and nonhuman primates: consequently, making comparisons often relies on comparing findings from different studies. However, we show that human and nonhuman gestural research has followed different approaches, making comparisons challenging. We describe and employ a similar methodology to explore how gestures are accommodated in two chimpanzee communities and four groups of humans (toddlers). Within this evolutionary framework we explore both the ability to accommodate communication from a broad perspective by looking at how chimpanzees communicate across different relationships during greetings and leave-takings, and the in-depth exploration of the gestural communication of chimpanzee mothers with their infants and other community members. We found that social aspects of relationships, such as kinship and rank, influence the likelihood of communication, and that kinship shapes more subtle features of the gestures produced, such as prominence and temporal patterns. We examined nuanced features of gestural communication in both chimpanzees and humans in the light of work on Child-Directed Communication (CDC) in language. Chimpanzee mothers accommodated their communication towards young individuals, but in different ways to CDC accommodation in adult use of language: they used shorter gesture units towards immature individuals and used more repetition towards older offspring. Taking a developmental perspective, we found that CDC emerged early in ontogeny, before language, with toddlers using a simpler gestural vocabulary and gesturing at a slower pace towards younger peers. We show that the ability to accommodate our communication, including to young individuals, is present in gestural communication of chimpanzees and preverbal children, suggesting that this ability is not a mere consequence of language but instead represents one of the foundational capacities on which language use is built. We share this ability to accommodating our communication with chimpanzees, and it was likely present in our last common ancestor, but different selective pressures may have shaped the expression of this ability in the two species.
Description
Tese apresentada para cumprimento dos requisitos
necessários à obtenção do grau de Doutor em Biologia
do Comportamento
apresentada no Ispa - Instituto Universitário no ano de
2023.
Keywords
Gestos Acomodação Chimpanzés Crianças Gestures Accommodation Chimpanzees Toddlers