Genes are switches, not a fixed blueprint

Ridley's central corrective to popular misunderstanding is that genes don't function like an architectural blueprint executed once and for all at conception. Most genes are more like switches that get turned on or off throughout life in response to signals from the body and the environment — hormones, nutrition, stress, even social experience can flip genetic activity on or off. A gene for producing a particular protein might sit dormant for years until a specific trigger activates it. This means the same genome can produce different outcomes depending on when and where its instructions are read, and it explains phenomena like identical twins developing different disease risks or personalities despite sharing DNA. The metaphor of a "blueprint" implies a single, static plan executed passively; Ridley prefers the metaphor of a recipe or a script that gets performed differently depending on the conditions of the performance. This reframing dissolves much of the false dichotomy between genetic determinism and environmental influence. Takeaway: DNA doesn't dictate outcomes on its own — it responds, continuously, to context.