Phylogenetic trees are often used to track what evolved from what.
        
             
        
        
        
Having one theory is setting a limit on your potential and the potential of the overall theory and subject you are working on. Having multiple theories gives you a broader idea and perspective of what is going on, and even though one may slightly contradict the other, it is okay because that is what theories are for.
To the point, scientists usually have more than one theory so that they can gain a broader perspective on the matter and maybe even increase the chance of being correct on the matter. 
Hope this was helpful.
Cheers,
 
        
             
        
        
        
Answer:
commensalism
Explanation:
One organism is benefited while the other is not harmed or benefited.
 
        
                    
             
        
        
        
For example:  GGATACCTAGGTAAT
Insertion: GGAT<u>G</u>ACCTAGGTAAT
a nucleotide that was not present before is inserted into the original sequence
Substitution: <u>C</u>GATACCTAGGTAAT
the first nucleotide was substituted in for another (C for G)
Frameshift (basically a insertion or deletion, we'll try deletion here): GATACCTAGGTAAT
the first nucleotide was deleted, causing the reading frame to be shifted (instead of GGA as the first codon, we have GAT)