The Harmony relationship is like a stable ecosystem. It is balanced, predictable, and highly sustainable. There may be neither dramatic differences nor intense resonance between the two, but in their place lie deep trust and a sense of security. As the foundation for a long-term relationship, this is extraordinarily valuable. From a neuroscience perspective, the Harmony relationship optimizes the balance of oxytocin and serotonin. Levels of the stress hormone cortisol are kept low, and the parasympathetic nervous system predominates. This is an important factor in extending healthy lifespan. Even without intense passion, a gentle sense of well-being endures -- and this may, in fact, be the single most important element of human happiness.