²⁴This is what is called “exaptation” in evolution. It means that a trait was first produced to adapt for one phenomenon, but then it turned out to be useful for something else. A typical example is bird’s feathers, which probably first evolved to keep the birds warm, and only later turned out to be useful for flying. Wagner et al. (2003) discuss computer simulations on the emergence of language for communication between agents. Dehaene et al. (2022) propose that the main capacity specific to humans is using symbols and mental programs, generalizing the idea that language and sequence processing is specific to humans. For an attempt to do some kinds of logical processing in a neural system, see Frady et al. (2020).