Are Viruses Alive?

One longstanding debate in the field of biology is whether or not viruses should be considered alive.  Viruses are composed of a protien coat with some form of genetic material contained on the inside.  Unlike all other species not debated as "living," viruses lack the ability to reproduce on their own because of their simple design.  Instead, viruses are only able to reproduce or replicate within a host.  They use the machinery present in their host cells to replicate and spread the virus.  For those who believe viruses are not alive, this is the main point they cite.  Without a host cell, virsuses would not be able to survive therefore should not be considered alive.  The opposition believes viruses should be considered alive because of the success they have at infultrating thier hosts and reproducing.  Like all other species considered alive, success by a virus should be determined by their reproductive fitness.  Those who are not fit are removed from the population while those fit to survive pass on their ability to the next generation.  The niche that viruses find themselves in the ecosystem is one that they have remained in since their discovery.  Yes, they need a host but a host is their niche.  If they were not fit for this niche they would not survive or exist in the living world but they do.