Jeff Schweitzer states in "Redefining Life: God Need Not Apply" (2010-06-02):
"the fact that scientists have discovered no simple quality that defines life, after endless years of effort, is an important hint that life is not something materially different from non-life but instead represents a natural place in a continuum from simple to complex. History has failed to give us a good definition precisely because life was viewed not on this continuum from inanimate to animate, but as a huge leap from one to the other. To be alive meant having a special essence, something beyond the normal mechanisms that governed inorganic chemistry and physics. The tendency to invoke 'vital forces' to explain life endures today in much of the general public [...such] vitalism, the principle of endowing the living with a life force, is tautological and explains nothing. If something is alive, it must have a life force; if it is dead, a life force must be absent. That is not helpful. We now know that no life force exists. The laws of physics and chemistry are indifferent to our struggle to define life, and operate identically on the same principles whether we deem something to be living or dead. The carbon, nitrogen, phosphorous, iron and other atoms that come together to form our bodies are just atoms; they are the same elements that are found in the iron skillet in our kitchens and the nitrogen in the soil fertilizing our gardens. The atoms in our bodies are not special or endowed with any properties different from the atoms in every object around us. Iron is iron is iron, whether attached to hemoglobin in our blood or flaking off the hull of a rusting ship."
Note: right down my alley. Naturopathy, of course, instead claims that a life force is a scientific fact.