<P> The definition of life is controversial . The current definition is that organisms maintain homeostasis , are composed of cells , undergo metabolism , can grow , adapt to their environment , respond to stimuli , and reproduce . However , many other biological definitions have been proposed , and there are some borderline cases of life , such as viruses . Throughout history , there have been many attempts to define what is meant by `` life '' and many theories on the properties and emergence of living things , such as materialism , the belief that everything is made out of matter and that life is merely a complex form of it ; hylomorphism , the belief that all things are a combination of matter and form , and the form of a living thing is its soul ; spontaneous generation , the belief that life repeatedly emerges from non-life ; and vitalism , a now largely discredited hypothesis that living organisms possess a `` life force '' or `` vital spark '' . Modern definitions are more complex , with input from a diversity of scientific disciplines . Biophysicists have proposed many definitions based on chemical systems ; there are also some living systems theories , such as the Gaia hypothesis , the idea that the Earth itself is alive . Another theory is that life is the property of ecological systems , and yet another is elaborated in complex systems biology , a branch or subfield of mathematical biology . Abiogenesis describes the natural process of life arising from non-living matter , such as simple organic compounds . Properties common to all organisms include the need for certain core chemical elements to sustain biochemical functions . </P>
what are the criteria for something to be considered living
maintain homeostasis are composed of cells undergo metabolism can grow adapt to their environment respond to stimuli and reproduce However , many other biological definitions have been proposed