Periodicity is the engine that has driven the explosion of life on this planet. The days and nights, the tides, the cycle of the years, the sunspots and El Nino... dust bowls, mini-Ice Ages, floods, ice ages, catastrophic events such as meteor hits, plagues, earthquakes, ... All of these events have challenged all forms of life and forced them to adapt and become better at survival. And all along the way the memories of how to transcend these life-threatening challenges have been recorded in DNA - parents teaching children - and human society - patiently recording how to face the future. And carry on.