Why are the brains of synaesthetes so ‘communicative’ and how exactly do synaesthetic sensations form? ‘Where does synaesthesia come from? The role of genetics and learning’ asks whether synaesthesia is pre-determined in the genes, or based on learning from the environment by considering synaesthetic associations, synaptic pruning, and the Neonatal Synaesthesia Hypothesis. It shows that synaesthesia emerges over time, that it can follow rules based on information absorbed from the environment with these rules sometimes shared by non-synaesthetes, and that synaesthesia has a likely genetic inheritance. It concludes that synaesthesia derives not only from post-birth events such as literacy acquisition and environmental submersion, but is also likely to be predetermined in some way at birth.