Learn about the molecular basis of evolution with this video that supports NOVA’s Evolution Lab game. DNA weaves together the tapestry of life on Earth. DNA contains the blueprints for creating different organisms. When DNA is copied, it sometimes mutates, leading to variation among organisms. Variation in expressed traits may affect how an organism survives in its environment. For example, polar bears are more suited for Arctic life than brown bears, thanks to genes for lighter fur and better insulation. Mutations happen randomly and are not necessarily helpful.