Secondly, the essay confronts the question of cognition and ontology, suggesting that the human brain is not inherently distinct from the brains of other mammals, but that human intellectual capabilities developed through a dialectical relationship with the human body. Specifically, Engels emphasizes the importance of humans’ opposable thumbs and phonetically dynamic mouths, which enabled them to articulate complex forms of language over time. In that respect, the essay challenged the prevailing philosophy of Cartesian dualism, which drew a stark division between mind and body.