Coronavirus, flu and so on are living beings, many people intuitively assume. But actually they are not – or are they? How viruses can be assigned is a tricky question: we are dealing with tiny “border crossers”.
They infect us and make us sick – you might think that viruses seem to resemble bacteria. But they differ fundamentally from the microbes: In contrast to these unicellular organisms, virus particles are actually just packaged genetic material: DNA or RNA, which is surrounded by a protein-containing shell. Organelles such as mitochondria, ribosomes and cell plasma, on the other hand, do not have viruses. They therefore lack two basic characteristics of living things: viruses do not metabolize and cannot multiply on their own.
Lifeless genetic engineers
Therefore, these functions must be carried out by others. To make this possible, viruses infiltrate their blueprints into the genetic material of host cells and thereby make them their factories: the victim produces further virus particles, which then go on the journey to hijack additional cells. In this way, viruses cause various diseases in humans. However, some also infect bacteria – this makes the difference between the two pathogen types particularly clear.
Against this background, viruses can be viewed as lifeless bioparticles. That is why some biologists exclude them from the living being community. But there are also arguments that speak for an association with life. Because viruses have one characteristic of the living: they have the ability to develop genetically – for example through mutations that enable them to adapt. In addition, one can be of the opinion that viruses are part of life, at least in the integrated state: as soon as their blueprint is built into the DNA of a host cell, they become part of a living system.
Living ancestors?
However, some researchers go even further: they argue for the classification of viruses in the family tree of life. The reasoning: There are indications that viruses once developed from living things. This is shown by comparing the protein molecules of bacteria with those produced by the viral DNA. They suggest that distant ancestors of the virus were still real cells. Only when they became cell parasites did they save the cell machinery and use that of their hosts, so the assumption. From this point of view, viruses would be living beings that have produced a bizarre method of reproduction through the reduction of traits.
The existence of so-called giant viruses also seems to speak for the thesis. In contrast to tiny things such as corona viruses or flu agents, they can grow as large as some types of bacteria and carry a very extensive genome. Protein folding patterns of these giant viruses also show striking parallels to those of microbes. The assumption is that they could still be relatively similar to the cellular precursors of all viruses.
Ultimately, however, it remains a matter of opinion whether the bizarre giant viruses or pathogens such as Sars-CoV-2, HIV or Ebola are assigned to living beings or not. However, it is clear that viruses have had an enormous impact on the developmental history of life – and also on human history.