Multiple origins of life.
There is some indication that life may have originated readily under primitive earth conditions. If there were multiple origins of life, the result could have been a polyphyletic biota today. Using simple stochastic models for diversification and extinction, we conclude: (i) the probability of survival of life is low unless there are multiple origins, and (ii) given survival of life and given as many as 10 independent origins of life, the odds are that all but one would have gone extinct, yielding the monophyletic biota we have now. The fact of the survival of our particular form of life does not imply that it was unique or superior.
D005075:Biological Evolution; D002470:Cell Survival; D008954:Models, Biological; D000069497:Origin of Life; D011336:Probability; D011387:Prokaryotic Cells / Q000502:physiology