Longevity is determined by the function of our genes. The word "organism" originates from the root "organ" that stems from the Greek for tool or instrument. The genome is simply another organ that serves the whole organism. Therefore, longevity is a decision influenced by the brain and the immune system, both being responsible for health and disease, life and death. The metabolic system acts as a bridge between the brain and the immune system. Leptin, as a cytokine-like protein, is well-known for its multiple hormonal functions in metabolic regulation, but it is increasingly recognised for its even more fundamental role, hence our reference to it as "permitine" (= the permitting hormone). As the master regulator of all cytokines, it plays a crucial role in providing agency and purpose.