In the evolutionary progression, each stage of development, while maintaining the Oneness of the entire creation, permits various forms of variation in the expression of the different elements or beings within the creation. At the material level, everything is very much fixed and follows basic laws with very little variation, within the framework of the various types of material substance that have been created. At the vital stage, we see variation within the type so that different plants and animals, while following the law of its type, may still express variations in shape, color, size, resiliency, and individual reaction, etc. At the human stage, with the advent of the mental principle in evolution, we see yet further ability to diverge from a fixed expression, even while the underlying principle of Oneness and the overarching laws of the created universe remain in place. In further stages of development we may see a more free-flowing unity with diversity at work.
Sri Aurobindo observes: “It (existence) begins, at least in our field of existence, with a material figure of itself, a mould of firm substance into which and upon which it can build, — worlds, the earth, the body. Here it stamps firmly and fixes the essential law of its movement. That law is that all things are one in their being and origin, one in their general law of existence, one in their interdependence and the universal pattern of their relations; but each realises this unity of purpose and being on its own lines and has its own law of variation by which it enriches the universal existence. In Matter variation is limited; there is variation of type, but, on the whole, uniformity of the individuals of the type. These individuals have a separate movement, but yet the same movement; subject to some minute differences, they adhere to one particular pattern and have the same assemblage of properties. Variety within the type, apart from minor unicities of detail, is gained by variation of group sub-types belonging to one general kind, species and sub-species of the same genus. In the development of Life, before mind has become self-conscious, the same law predominates; but, in proportion as life grows and still more when mind emerges, the individual also arrives at a greater and more vital power of variation. He acquires the freedom to develop according, no doubt, to the general law of Nature and the general law of his type, but also according to the individual law of his being.”
Sri Aurobindo, The Human Cycle: The Psychology of Social Development, Chapter 7, The Ideal Law of Social Development, pp. 63-64