<P> Each level in the hierarchy can be described by its lower levels . For example, the organism may be described at any of its component levels, including the atomic, molecular, cellular, histological (tissue), organ and organ system levels . Furthermore, at every level of the hierarchy, new functions necessary for the control of life appear . These new roles are not functions that the lower level components are capable of and are thus referred to as emergent properties . </P> <P> Every organism is organised, though not necessarily to the same degree . An organism cannot be organised at the histological (tissue) level if it is not composed of tissues in the first place . </P> <P> Empirically, a large proportion of the (complex) biological systems we observe in nature exhibit hierarchic structure . On theoretical grounds we could expect complex systems to be hierarchies in a world in which complexity had to evolve from simplicity . System hierarchies analysis performed in the 1950s, laid the empirical foundations for a field that would be, from the 1980s, hierarchical ecology . </P> <P> The theoretical foundations are summarized by thermodynamics . When biological systems are modeled as physical systems, in its most general abstraction, they are thermodynamic open systems that exhibit self - organised behavior, and the set / subset relations between dissipative structures can be characterized in a hierarchy . </P>

Where did the organization of living come from