If this is true the basic observation leading to the theory  Digestive Enzymes would be invalid The theory has gained significant popularity as a way of explaining rapid changes in adaptation that cannot otherwise be explained by traditional mechanisms of natural selection Within the hologenome theory the holobiont has not only become the principal unit of natural selection but also the result of other step of integration that it is also observed at the cell symbiogenesis endosymbiosis and genomic levels Research methods  Targeted amplicon sequencing Targeted amplicon sequencing relies.