Abstract
Language is central to the cognitive and sociocultural traits that distinguish humans, yet the evolutionary emergence of this capacity is far from fully understood. This review explores how the study of the brains of language-trained apes (LTAs) offers a unique and valuable opportunity to tease apart the relative contribution of evolved species differences, behavior, and environment in the emergence of complex communication abilities. For example, when raised in sociolinguistically rich and interactive environments, LTAs show communicative competencies that parallel aspects of early human language acquisition and exhibit altered neuroanatomy, including increased connectivity and laterization in regions associated with language. Sustained and enriched early exposure to symbolic experience may also alter molecular pathways, including modifications in the expression of genes involved in synaptic plasticity, neural connectivity, and cognitive function, thus critically underpinning speech and language processing. This theoretical synthesis highlights how research on language-trained apes can inform our understanding of experience-dependent plasticity in distributed neural networks, providing insights into the evolutionary origins of human communication.