Explorer writes:
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.
Be careful with this, though. The way natural selection is viewed isn't actually "survival of the fittest," but "survival of the fit
enough". There isn't any natural law that says the upstart can't win, or that the upstart can't survive. Birds evolved during a time when the skies were filled with already well-adapted pterosaurs. Bats evolved during a time when the skies were filled with already well-adapted birds. However, as you say, the upstart is generally at a disadvantage when trying to compete with something that has been in place and well-adapted for a long time.
Also keep in mind that the earliest fossils consist of microscopic structures that resemble bacterial cells and lumps of rock called stromatolites, which generally form from piles of photosynthetic bacteria that died when new bacteria grew on top of them and blocked the sunlight. We can't actually confirm exactly what made the stromatolites, because their molecular structures didn't fossilize. Because they kind of resemble bacteria in appearance and, based on the minerals of the stromatolites, metabolism, we generally classify them as bacteria. But, there could have been other types of alternatively-evolved organisms that created stromatolites at the same time.
However, it seems infinitely more probable that all the living things around today are related, and science will generally stick to that answer until we find reason to doubt it (and we haven't yet).
Edited by Bluejay, : Added three random words
Signed,
Nobody Important (just Bluejay)
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