article source: http://www.byzant.com/Mystical/Symbols/Spiral.aspx
The spiral is the most common shape in nature and is an ancient spiritual symbol of growth and evolution. Spirals occur naturally in shells, galaxies, DNA, whirlpools and countless other instances, and the human history of the shape stretches back beyond the ancient Celts and Greeks. In two dimensions, a spiral is a curve that winds around a fixed point at a continuously increasing or decreasing distance from that point. Thus the spiral represents the bringing forth of life from a central point (cf. Kether on the Kabbalistic Tree of Life) as it unwinds, or a return to the center of creation in the other direction. In this latter aspect it embodies the labyrinth that leads to the divine center. It is a symbol of evolution, self-transformation and the forces and patterns underlying creation.
A spiral that winds around its center in a clockwise direction may be considered constructive and one that moves in the opposite direction destructive. Spirals are found in Biblical whirlwinds, in ceremonial dances (an inward then outward spiral represents the cycle of death and rebirth) and in the gyres of Yeats' poetry.