I really don't know what to make of this paper I just stumbled upon, The Structures of Letters and Symbols throughout Human History Are Selected to Match Those Found in Objects in Natural Scenes:
...Our first result is that these three classes of human visual sign possess a similar signature in their configuration distribution, suggesting that there are underlying principles governing the shapes of human visual signs. Second, we provide evidence that the shapes of visual signs are selected to be easily seen at the expense of the motor system. Finally, we provide evidence to support an ecological hypothesis that visual signs have been culturally selected to match the kinds of conglomeration of contours found in natural scenes because that is what we have evolved to be good at visually processing.
The authors note that a counterintuitive inference from their results is that human letters & symbols when placed in natural settings will be harder to detect. Their development on artificial uniform surfaces (paper, clay tablets, etc.) though makes them maximally appealing and triggers our sensory biases. The authors allude to an analogy with sexual selection, adaptive predispositions or mild biases may be utilized by novel phenotypes to spread throughout a population. In The Symbolic Species neurobiologist Terrence Deacon makes the argument perception of the existence of a universal grammar in linguistics is an artifact of the selective adaptation of languages onto the contours of our minds. That is, instead of languages emerging straight-jacketed by the parameters of the unviersal grammar, they slowly converge upon the cognitive optimum via a process of cultural selection. Whether you believe in universal grammar or not, or accept the details of this research, the "big picture" point is that the idea that culture is an arbitrary set of rules and regulations shaped only by our interaction with the outside world is probably false. Culture emerges from our minds, and our mental biases serve as an important constraint and selective force in how culture expresses itself. There is likely an outward functionalist aspect of culture where successful adaptations (e.g., desert peoples passing on traditions of where to find water via a narrow set of heuristics) propogate, but there are also nearly inevitable cultural developments which are byproducts of the architecture of our brain.