Where did viruses come from?
That depends what you mean. If you point to a virus right now, over
there, in the corner of the room, stuck to a used tissue, and ask
where did THAT virus come from, then I have this answer: that virus
was made by a cell in an animal or plant's body. Some other virus
infected the cell, and ``hijacked'' the cell's nucleus, the command
center for the cell. Instead of instructing the cell to do what it's
supposed to do for the animal or plant, the virus forced the cell's
command center to instruct the cell to make copies of the virus. The
cell did so. Eventually the cell made so many new viruses that the
cell burst open, and all the new viruses escaped.
Where did the other virus come from? It, too, was made by an
infected cell, possibly a cell in the same animal, possibly a cell in
And where did THAT virus come from? Another infected cell. And so
forth and so on.
Does it ever stop? Is there a place where it all got started, where
there was nothing and then somehow a virus? Sort of. Each time the
virus is copied, it is changed a teensy bit. It may be a trifle
bigger, a smidgen more complex, a different color, whatever. Over a
very, very long time these changes can amount to quite a bit. A
million or a billion years ago, the viruses we know and hate could
have come from something a lot simpler, perhaps something as simple as
a single partially self-replicating molecule.
And where did THAT come from? This is the question of the origin of
life. There are several possibilities. One is that it came from
another planet, drifting through space on a meteorite perhaps.
Another is that it was created by accident by some of the violent
things that occurred on the early Earth, like lightning, volcanoes, or
meteor strikes. No one really knows, because no one was around to
watch in those days. It is possible perhaps to find out, if we go
look for a planet out there on which this is happening today.
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Update: June 2012