Engels uses this framework to suggest that humanity must transcend the ecologically destructive patterns of capitalism, and progress to a mode of production that operates in harmony with nature.
Specifically, Engels emphasizes the importance of humans’ opposable thumbs and phonetically dynamic mouths, which enabled them to articulate complex forms of language over time.
[citation needed] Marx and Engels had both alluded to this notion in previous writings, for instance in their first collaborative work, The Holy Family, in which they wrote, "Body, being, substance are but different terms for the same reality.
Anyone who has had much to do with such animals will hardly be able to escape the conviction that in many cases they now feel their inability to speak as a defect, although, unfortunately, it is one that can no longer be remedied because their vocal organs are too specialized in a definite direction.” He goes on to suggest that parrots can, to a limited extent, comprehend human language – a hypothesis that has been substantiated by scientific studies.
Stephen Jay Gould has argued that this is the only scientifically sound theory of the evolution of the human brain, and stated that Engels’ essay made “the best nineteenth-century case for gene-culture coevolution.”[6]