Complex sentence: If two species are similar and live side by side, then the survival of one species becomes less important for the pathogen, and in the end it may have three outcomes: divergence, exchange of genes, downfall.
Split into simpler sentences: If two species are similar and live side by side, then the survival of one species becomes less important for the pathogen. And in the end it may be three outcomes: divergence, exchange of genes, downfall.