Decoding the architecture and origins of mechanisms for developmental polyphenism

•Functional studies have revealed specific genes regulating polyphenism in animals.•Findings suggest genetic conditions for how polyphenism switches arise in evolution.•Studies on thresholds and downstream genes give insight into polyphenism evolution. Developmental polyphenism affords a single genotype multiple solutions to match an organism to its environment. Because polyphenism is the extreme example of how development deviates from a linear genetic blueprint, it demands a genetic explanation for how environmental cues shunt development to hypothetically alternative modules. We highlight several recent advances that have begun to illuminate genetic mechanisms for polyphenism and how this recurring developmental novelty may arise. An emerging genetic knowledge of polyphenism is providing precise targets for testing hypotheses of how switch mechanisms are built—out of olfactory, nutrient-sensing, hormone-reception, and developmental and genetic buffering systems—to accommodate plasticity. Moreover, classic and new model systems are testing the genetic basis of polyphenism's proposed causal roles in evolutionary change.