Spirit does not give birth to spirit. Spirit is the energy that is created from the lifeforce of the Infinite Creator. All things have at their source the Infinite Creator regardless of their level of awareness.
For example, a tree has a vital energy source/spirit which flows through it and gives it life. This energy connects with everything (both physical and non-physical) including the source of creation. To continue the analogy; the tree, whilst it may produce offspring the central life-giving source of the offspring is not from the physical tree but from the vital energy source which flows through it.