My Life
It is important to note that life is a definition that applies primarily at the level of species, so even though many individuals of any given species do not reproduce, possibly because they belong to specialized Sterile castes (such as ant workers), these are still considered forms of life. One could say that the property of life is inherited; hence, sterile hybrid species such as the mule are considered life although not themselves capable of reproduction. It is also worth noting that non-reproducing individuals may still help the spread of their genes through such mechanisms as kin selection.
For similar reasons, viruses and aberrant prion proteins are often considered replicators rather than forms of life, at distinction warranted because they cannot reproduce without very specialized substrates such as host cells or proteins, respectively. However, most forms of life rely on foods produced by other species, or at least the specific chemistry of Earth's environment.
Some individuals contests such definitions of life on philosophical grounds, and offer the following as examples of life: viruses which reproduce; flames which "grow"; certain computer software programs which are programmed to mutate and evolve; future software programs which may evince (even high-order) behavior; machines which can move; and some forms of proto-life consisting of metabolizing cells without the ability to reproduce.
Still, most scientists would not call such phenomena expressive of life. Generally all six characteristics are required for a population to be considered a life form.