Biological organization, is the hierarchy of complex biological structures and systems that define life using a reductionistic approach. The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of this scheme are often referred to as ecological organization.
Each level in the hierarchy represents an increase in organizational complexity, with each "object" being primarily composed of the previous level's basic unit. The basic principle behind the organization is the concept of emergence—the properties and functions found at a hierarchical level are not present and irrelevant at the lower levels.
Organization furthermore refers to the high degree of order of an organism (in comparison to general objects). Ideally, individual organisms of the same species have the same arrangement of the same structures. For example, the typical human has a torso with two legs at the bottom and two arms on the sides and a head on top. It is extremely rare (and usually impossible, due to physiological and biomechanical factors) to find a human that has all of these structures but in a different arrangement.
The biological organization of life is a fundamental premise for numerous areas of scientific research, particularly in the medical sciences. Without this necessary degree of organization, it would be much more difficult—and likely impossible—to apply the study of the effects of various physical and chemical phenomena to diseases and physiology (body function). For example, fields such as cognitive and behavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts of pharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism. These applications extend into the ecological levels as well. For example, DDT's direct inseciticidal effect occurs at the subcellular level, but affects higher levels up to and including multiple ecosystems. Theoretically, a change in one atom could change the entire biosphere.
The simple standard biological organization scheme, from the lowest level to the highest level, is as follows:
| A-cellular level
|* The atom|
|* The molecule, a grouping of atoms|
|* The biomolecular complex, a grouping of (bio)molecules|
|Sub-cellular level||* The organelle, a functional grouping of biomolecules; biochemical reactions and interactions|
|Cellular level||* The cell, the basic unit of all life and the grouping of organelles|
| Super-cellular level
|* The tissue, a functional grouping of cells|
|* The organ, a functional grouping of tissues|
|* The organ system, a functional grouping of organs|
|* The organism, the basic living system, a functional grouping of the lower-level components, including at least one cell|
|* The population, a grouping of organisms of the same species|
|* The community (or biocoenosis), a interspecific grouping of interacting populations|
|* The ecosystem, a grouping of organisms from all biological domains in conjunction with the physical (abiotic) environment|
|* The Biome, a continental scale (climatically and geographically contiguous areas with similar climatic conditions) grouping of ecosystems.|
|* The biosphere or ecosphere, all life on Earth or all life plus the physical (abiotic) environment|
More complex schemes incorporate many more levels. For example, a molecule can be viewed as a grouping of elements, and an atom can be further divided into subatomic particles (these levels are outside the scope of biological organization). Each level can also be broken down into its own hierarchy, and specific types of these biological objects can have their own hierarchical scheme. For example, genomes can be further subdivided into a hierarchy of genes.
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.
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.
When biological systems are modeled as physical systems, in its most general abstraction, they are thermodynamic open systems that exhibit self-organized behavior, and the set/subset relations between dissipative structures can be characterized in an hierarchy.
Another way, more simple and direct to explain the fundamentals of the "hierarchical organization of life", was introduced in Ecology by Odum and others, as the "Simon's hierarchical principle". Simon emphasized that hierarchy was something profoundly natural. Hierarchy, he argued, "emerges almost inevitably through a wide variety of evolutionary processes, for the simple reason that hierarchical structures are stable".
To motivate this deep idea, he offered his "parable" about imaginary watchmakers.
Parable of the Watchmakers
There once were two watchmakers, named Hora and Tempus, who made very fine watches. The phones in their workshops rang frequently; new customers were constantly calling them. However, Hora prospered while Tempus became poorer and poorer. In the end, Tempus lost his shop. What was the reason behind this?
The watches consisted of about 1000 parts each. The watches that Tempus made were designed such that, when he had to put down a partly assembled watch (for instance, to answer the phone), it immediately fell into pieces and had to be reassembled from the basic elements.
Hora had designed his watches so that he could put together subassemblies of about ten components each. Ten of these subassemblies could be put together to make a larger sub-assembly. Finally, ten of the larger subassemblies constituted the whole watch. Each subassembly could be put down without falling apart.
- Cell theory
- Cellular differentiation
- Composition of the human body
- Evolutionary biology
- Holon hierarchy
- Human ecology
- Living systems
- Spontaneous order
- Solomon, Berg & Martin 2002, pp. 9–10
- Pavé 2006, p. 40
- Postlethwait & Hopson 2006, p. 6
- Huggett 1999
- Pavé 2006, p. 39
- Postlethwait & Hopson 2006, p. 7
- Simon, H. A. (1969). The architecture of complexity. In The Sciences of the Artificial (pp. 192-229). Cambridge, MA: MIT Press.
- Simon's texts at polaris.gseis.ucla.edu/pagre/simon or johncarlosbaez/2011/08/29 transcriptions
- Griswold, Joseph G.; McDaniel, Nichole (Spring 2006), "Module 1:Overview and Hierarchy of Life", Progressions (New York, New York) 7 (3), ISSN 1539-1752
- Pavé, Alain (2006), "Biological and Ecological Systems Hierarchical Organization", in Pumain, Denise, Hierarchy in Natural and Social Sciences, New York, New York: Springer-Verlag, ISBN 978-1-4020-4126-6
- Postlethwait, John H.; Hopson, Janet L. (2006), Modern Biology, Holt, Rinehart and Winston, ISBN 0-03-065178-6
- Solomon, Eldra P.; Berg, Linda R.; Martin, Diana W. (2002), Biology (6th ed.), Brooks/Cole, ISBN 0-534-39175-3, LCCN 2001095366
- Huggett, R. J. (1999). "Ecosphere, biosphere, or Gaia? What to call the global ecosystem. ECOLOGICAL SOUNDING". Global Ecology and Biogeography 8 (6): 425–431. ISSN 1466-822X. doi:10.1046/j.1365-2699.1999.00158.x.
- 16x16px Cell physiology (in Human Physiology) at Wikibooks
- 16x16px Characteristics of life and the nature of molecules (in General Biology) at Wikibooks
- 16x16px Organization within the biosphere (in Ecology) at Wikibooks