It’s a common question in biology classrooms: are viruses alive? Often, the quick answer, especially for those studying introductory biology, is no. This is largely because viruses fail to exhibit all seven characteristics traditionally associated with life: Movement, Respiration, Sensitivity, Nutrition, Excretion, Reproduction, and Growth.
Yet, viruses possess genetic material in the form of DNA or RNA, a hallmark of every living organism on Earth. This begs the question – does having genes qualify them as ‘alive’? To understand this, we need to delve deeper into the biological definition of life itself.
Consider dogs, undeniably living beings. They grow, reproduce, derive energy from food, move, and react to their surroundings. They also excrete waste. Viruses, however, don’t tick all these boxes.
Viruses are incapable of independent movement, growth, metabolism to produce energy, or waste removal. However, they undeniably reproduce, invading organisms and causing diseases. It’s their unique method of reproduction that sets them apart.
Viruses lack the necessary cellular machinery for self-replication. Instead, viruses can only replicate by invading a living cell – a process known as viral replication. Once inside a host cell, viruses hijack the cell’s mechanisms to synthesize viral proteins and genetic material, essentially creating copies of themselves. Some viruses, known as enveloped viruses, even take a layer of fat from the host cell as they bud out. These newly formed virus particles then proceed to infect more cells, turning them into virus-producing factories.
Therefore, viral reproduction is fundamentally different from that of living organisms. Even single-celled bacteria can reproduce independently outside of a host, but viruses can only survive for a limited time outside a host cell. For instance, when someone infected with a cold virus sneezes, viruses can be transferred to surfaces like doorknobs. However, the longer the virus remains on the doorknob, the less likely it is to cause a new infection.
Another defining characteristic of life is the capacity for populations to evolve over generations through genetic changes. Dogs, for example, evolved from wolves, transforming from wild hunters to domestic companions. But what about viruses? Do they evolve?
