Final answer:
Viruses are not considered living because they lack cellular structure, cannot replicate without a host cell, and do not have their own metabolism or maintain homeostasis.
Step-by-step explanation:
Viruses are not considered living because they lack cellular structure, cannot replicate without a host cell, and do not have their own metabolism or maintain homeostasis. While they do contain genetic material and can evolve, these traits alone are not enough to classify them as living organisms.
Viruses are not considered living because they lack cellular structure; specifically, they are not made of cells and thus lack cell membranes, cytoplasm, ribosomes, and other cell organelles. They also cannot replicate on their own and must infect a host cell to reproduce, which classifies them as obligate intracellular parasites. Despite not being living, viruses do contain genetic material, either DNA or RNA, and they are capable of evolving over time. This evolutionary capability is one of the few traits that viruses share with living organisms, complicating the classification of viruses and the definition of life.