Fundamental characteristics of life include several components. For the purpose of this article all life forms will be called organisms. Organisms consist of at least one cell, and fall into one of six kingdoms. Plants, animal and fungi are three of these, and on the smaller scale are Eubacteria, Protista, and Archaebacteria.
There are many insects on earth, but the micro-organisms of the small scale life forms known as bacteria are much more plentiful. The human body is at least 90 percent microbial and just 10 percent of it is comprised of human cells.
So although human beings are certainly qualified as being alive, they are by no means alive without supporting a micro-biome that is also thriving with vitality.
To be considered alive, however, strict criteria must be met. There are six basic criteria that all six organisms of the kingdoms above share. Although most organisms are collections of more than just living cells, they have a DNA structure, or hierarchy. They also have responsiveness, or sensitivity as, say, a plant to sunlight.
Organisms also must have a regulatory system,that handles the processes of heat, respiration, nutriment supply, waste elimination and internal transport of these features.
This is also known in biology as homeostasis, or a balancing return to optimum status.
Metabolism, or regulation of energy, is the next feature required for an organism to be considered living. Plants, for instance, must be able to process sunlight and soil into cells. Most earth organisms regulate these processes with use of water.
Finally, a requirement for all life is potential for evolution and adaptation. Over time, the changing environment selects favored traits and organisms adapt to new conditions.
In modern day technology the idea of artificial life arises. Could a silicone based, or robotic, intelligence qualify as a life form? What about interactive systems themselves; if the human body is a collection of hydrology, electro-chemistry and interactive bacterial and cellular systems, why couldn’t a planet then, be classified as a living entity? And what about processes like storms and fires, these too share interactive chemistry, states and phases and dynamic tendencies.
Science is very interested in these possibilities, but for the purpose of known life on the planet as evolved over the last few billion years, the organic criteria for fundamental life remain structural, responsive, regulating, self metabolizing and evolving.
