This chapter will focus on the deep evolutionary history of the cognitive capacities underlying linguistic iconicity. The complex capacity for linguistic iconicity has roots in a more general cross-modal ability present throughout the animal kingdom, cross-modal transfer. Cross-modal transfer is the ability to make basic inferences about sensory properties of an object in multiple modalities based on experience from only one. This situates iconicity as a fundamentally cross-modal phenomenon; part of a broader, uniquely human cross-modal cognitive suite which includes relatively rare phenomena like synesthesia, alongside more ubiquitous phenomena like sensory metaphor and cross-modal correspondences. Evidence suggests the evolutionarily deep capacity for cross-modal transfer was honed into more sophisticated capacities underlying iconicity by an evolutionary ratchet of increased prosociality during human self-domestication. This period provided strong selective pressures for increasingly complex cross-sensory communication, and eventually, the predominantly arbitrary symbolic systems that underpin modern human language.