Well... seems to me the most logical reason why we don’t see another line of evolution is that it would be extremely hard for an up comer to win or compete over something that already have taken its place on the planet.
You'd think. After all, the first thing life would do on arising from the "organic soup" would be to reproduce ... by eating all the soup.
First come, first served.
However . wouldn’t it be possible for emerging life to become parasitic on our line of evolution? Are there any possible candidates for such an “attack”?
Viruses? Depends on whether they're alive or not ... and on how they originated.
Shortly , I thought of this.. long time ago I read that there are some things that don’t qualify fully as life-forms but bear a close resemblance.
Well, there are viruses, beta prions, RNA species ... none of them can metabolize, and beta prions can't evolve either.
Whether or not they're life depends entirely on your definition of life.
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