Abstract:

Syntax refers to the phenomenon that an organism is able to form a new high-level language unit from several relatively low-level language units based on certain rules, it is an important characteristic of human communication system that distinguishes humans from other animals.

According to the saltation view, syntax is the ability developed by human ancestors alone after the differentiation with other primates in evolution. In the history of human evolution, there is no pre- syntax stage. The gradual view holds that syntax has an evolutionary continuity in the primate lineage. Although the brain systems responsible for complex syntax processing are unique to humans, the sequential learning that underlies syntax processing can be traced back to older primates, but it has been further enhanced in humans.

The ability of sequence learning to extract, summarize and generalize the abstract structural relations among multiple stimuli is an important cognitive basis for human to implement syntax processing. Numerous studies have shown that in artificial grammar tasks, many species of primate can summarize and master the sequence of stimuli. There has been a gradual evolution in sequence processing between other primates and humans. Comparative studies from neurobiology suggest that the neural mechanisms that support serial order processing and simple grammar stem from the more ancient brain regions that humans share with other primates. It is these brain regions that allow other primates to understand and master ordering in artificial grammatical tasks. The neural mechanisms that support hierarchical structure processing and complex grammar come from areas of the brain that are unique to humans and emerged much later in evolution. So though complex grammar is not present in other primate communication systems, the sequence learning on which human syntactic processing depend stems from a cognitive mechanism that has existed in the evolutionary history of primates.

The gradual view poses a challenge to the explanation of the origins of syntax: if simple sequential processing is common to primates, why should it be that only humans have evolved complex grammatical mechanisms based on it? Several hypotheses have tried to answer this question. The Lexical Limitation Hypothesis suggests that the emergence of unique syntax in humans stems from the growth of vocabulary. This theory emphasizes the pressure exerted on the evolution of grammatical mechanisms by ‘information content’, that is, the expansion of expressed content leads to structured language. The Event Perception Hypothesis holds that syntax originated from the way organisms mentally perceive and represent natural events. According to this theory, syntax is the product of the co-evolution of human event coding system and expression system. The Self-Domestication Hypothesis holds that syntax evolved from self-domestication. Offensive language can belittle your competitors and show your strengths at the same time. In the process of human self-domestication, verbal aggression gradually replaced physical aggression and became an alternative means of social competition. This shift, in turn, imposes feedback and evolutionary demands on language itself, leading to the emergence of syntax and complex language forms.

These theories discuss the evolutionary origin of grammar from different perspectives, but all of them have insufficient explanatory power. In the field of language evolution research, no theory has been able to fully answer the question of the origin of human syntax. In fact, it is not necessarily a single factor that has dominated syntax evolution. For example, self-domestication reduces interpersonal conflict and increases the frequency of mutual learning, communication and cooperation, thus creating a favorable environment for more knowledge sharing and information dissemination. Complex language allows community members to communicate with each other on interpersonal relationships, thus forming positive feedback on intimate relationships and cooperative alliances. Diversified social interaction makes human beings have a unique tendency of event perception. It was the interaction of different factors at different times that led to the eventual development of mature syntax mechanism in humans.

Future research should clarify whether the neural mechanisms found in artificial grammar tasks are common processors for hierarchical processing in all fields, and further explore the relationship between syntactic processing and semantic processing.

Key words: syntax, sequence learning, artificial grammar, evolutionary continuity, comparative studies