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  Definitions of life have interested philosophers since prehistory and, in many ways, technical advances in biology have done little to further our understanding of the nature of life. The French anatomist Marie-François-Xavier Bichat (1771 - 1802) defined life as ‘The sum total of functions which resist death’, but did not attempt to pin down the reasons for this ability. , Jean-Baptiste Lamarck (1744 - 1829) proposed that life was ‘organic movement’ made possible by organization and external stimulation. The force behind the organization which was clearly a characteristic of life was considered by most 19th-century philosophers to be beyond scientific explanation, though it was widely accepted that many of the processes of life could be explained in physical and chemical terms. , Claude Bernard (1813 - 1878) denied that life was the result of complexity of organization, claiming instead that it was the result of directed development. He stated five general characteristics of life which are still useful in modern definitions: Organization; Generation; Nutrition; Development; Death.

Historically, philosophers had reasoned that the vital force resided in certain organs, particularly the heart or the brain; in the 18th and 19th centuries there was a trend to consider the vital force as a property of tissues, cells or organic molecules. The physicist , Erwin Schrüdinger (1887 - 1961), in his book What is Life?, proposed that the genes held the answer, and the development of an understanding of molecular genetics is enabling scientists to explain some of the features of life which were previously considered, because of their inexplicability, to be evidence for a vital force.

Modern biology neither requires, nor permits, the idea of a life force and, as scientists become more specialized, scientific interest in the nature of life seems to recede because experimental science demands that biological functions be interpreted in terms of physical and chemical processes. However, this scientific view of life is disputed by some, largely on theological grounds while there are others, scientists among them, who hold that the idea of a life force and the explosion of life purely in physio-chemical terms are not mutually exclusive. RB

See also abiogenesis; biopoiesis; mechanism; organicism; panspermia; vitalism.Further reading Humberto Maturana, The Tree of Knowledge.



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