By Michael Marshall
A peculiar Antarctic microbe may offer a clue to one of the biggest mysteries in evolution: the origin of viruses.
The microorganism is host to a fragment of DNA that can build a capsule around itself. It may help solve the mystery of how viruses first arose.
Viruses are not like other life forms. Arguably, they are not alive at all. All other living things are made of cells: squashy bags filled with the other essential molecules of life. Cells are intricate machines that can feed and reproduce independently.
Viruses are much simpler. A typical virus is a small piece of genetic material encased in a shell called a capsid. On its own, a virus can do little. But if it enters a living cell, it starts making copies of itself. Viruses often harm their hosts: for instance, the human immunodeficiency virus (HIV) can cause AIDS when it infects a person.
Biologists have puzzled for decades about where viruses come from. Are they an older, simpler form of life – or are they parasites that arose only once cells had evolved?
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