From their initial existence in an environment class three forms of life require environmental stimulus upon the nervous system to build behaviors from the instinctual, and to give the cognitive structure to what will become the mature adult habits and manners of the particular species of animal. Behaviors from instincts such as beavers building dens, birds their nests; the fight or flight response. Within some species, deliberate or neglect behavior of a non-nurturing nature towards offspring is characteristic. This class of nervous system is responsible for the range of behaviors and social activity seen in a wide variety of animals intending their future and furthering their present existence.
Depicting variance and interplay between life forms comprising picture classes two and three, on land arachnids, lizards, and insects can be categorized within an upper strata of class two, with primates, canines, and felines comprising an upper class three status, and possessing the more intricate capacities for sensory involvement, integration, and interpretations of their outside environment. Within the aquatic, marine environments, jellyfish and Tardigrada can be categorized within the lower strata's of class two while dolphins, porpoises, and whales are observed with the more intricate nervous systems.
It can be said that of the life forms described to this point none can develop the symbolic conceptualizations or cognitive structures in their minds to know they are going to die as a course of their natural life. Such a cognitive ability would require the capacity within a nervous system to form symbolic conceptualizations pertaining to memories of births and deaths. The animal would have to bring the concept for the entity of time to definition upon itself, e.g. concepts such as yesterday and tomorrow are employed in deliberations using an objective state of mind. The capacity to develop linear, symbolic, cognitive structures ultimately leading to the recognition of the concepts of existence and nonexistence, etc., and then to form and appreciate the specialized conceptual constructs of Life and Death, these tasks can only be accomplished with human cognition.