I could draw a picture of how leaves falls, this could symbolize life, but just about anything living can symbolize life. The leaf grows on the tree's branch, grows to an enormous stature; with its best years behind, it's color fades back to earth and in a short time it's body travels too.
But only on the surface can life of a leaf be comparable to actual life. Just as life is, the leaves life is circular, just as life is. But a leaf is just a leaf. It is created by the tree for one purpose and one purpose alone, to capture sunlight for photosynthesis for the entire tree system. The leaf, by assignment at birth can not do anything else. It's fate is locked to laying in the sun and withering to obscurity.
This does not only happen with non-mobile life forms, look at the worker ant. A tool used by the queen, it spends its whole life searching for food, gathering food, and delivering food to the colony. It has no capacity to do anything else. The ant can not pursue other things. The ant, born a female, sans the egg laying organs from her body, must live out her life in service to her queen.
People are most likely the furthers creature away from the leaf or the ant. Yet I wonder if we are just as the leaf, doing one action to the system without conscience until life ends, sometime, just as this post without closure.