Moments of the same type form aggregations in an ascending series of complexity, groups, systems, communities, clusters, constellations. Isolated moments are organized into groups, groups into systems, systems into communities and communities into constellations. Groups are the simplest, while constellations are the highest and most complex of the aggregates. The firmness, the stability of organization stands in direct, relation to complexity, the more complex an aggregation the less stable it is.
The order of complexity also represents the order of development, so that the more complex is also the latest to appear in the course of evolution. Evolution and stability stand thus in inverse relation. What appears early in the course of development is less firmly organized than what appears later on. The whole tendency of evolution is from stability to instability. The order of growth and instability is in the ascending scale from groups, through systems, communities, to clusters, and constellations. The simpler sensori-motor reactions are, both ontogenetically and phylogenetically, the first to appear in the course of evolution and they are also more stable than the more complex sensori-motor reactions. We can possibly best realize the relation of instability to complexity of structure, if we regard life, including both physiological and psychic processes, as an ascending organization of sensori-motor reactions to the influences of the external environment.
The sensori-motor reactions represent a hierarchy of organized aggregations beginning in the lowest reflexes and culminating in the highest activity.
An illustration of the lower reflexes may be taken, such as the knee-jerk, the action of the bladder, persistaltic movements of the intestines, respiratory movements, heart-beats, and other organic activities. Association among these various reflexes may be taken as higher aggregates. The complex coordination of orientation and space adjustment, such as the maintenance of equilibrium, walking, running, jumping, flying, swimming, etc., represent more complex activity. A still higher aggregate is to be found in the association of groups and systems of sensori-motor reactions within the sphere of a sense-organ with the complex coordination of motor adjustment of the whole body. The highest aggregates are to be found in the association of all the motor reactions organized within the different spheres of sense-organs with the complex motor coordination of body-adjustments.
Simple sensori-motor reflexes, complex reflexes, sensori-motor coordinations, instinctive adaptations and intelligent adjustments, statically regarded, correspond to the classification of psycho-motor aggregates into groups, systems, communities, clusters, and constellations. In other words, the study of the sensori-motor constitution of the higher organized beings in their adult stages, reveals the presence and interrelation of moments. We find that the history of the use and growth of aggregates is in the order of their complexity. In ontogenesis we find that the simple reflexes appear first, then the association, the more complex sensori-motor coordination, later on the so-called instinctive adaptations begin to appear, while the intelligent adaptations appear late in the course of development.
The child at its birth is a purely reflex being; the different reflexes are not even associated, it is the medulla and the spinal cord that are principally active; the pupils react to light, the legs and hands react to more or less intense sensory stimuli, such as tickling, and sensori-motor reflexes to taste-stimuli are present. All of those reactions are isolated, incoordinated; they are so many simple groups of sensori-motor reflexes, even the sucking activity of the infant is largely of the sensori-motor reflex type; the child at its birth is a spinal being, and its moment consciousness is desultory, consisting of the desultory activities of isolated functioning sensori-motor groups.
Later on the reflex activity such as of the hands, legs, eyes become associated through the development of sight and kinaesthetic sensations; the eyes can follow an object, the hands become adapted to the seizing movements. Movements and body- coordination then begin to appear, such as turning the body to right or left, then sitting up, then creeping, standing, then walking, then talking, all involving more and more coordination of muscles and kinaesthetic sensations, aided by the association of sensations and sensori-motor reactions from different sense-organs. It is late in its history of development that the child begins to gain full control of its actions and adjustment to the stimuli coming from the external environment.