One most obvious characteristics of glycosites was that the increasing samples or cross-species reports would lead to more glycosites. There are many factors contributing to the existence of numerous glycosites in H1, H3 and H5 subtypes. Because the RNA virus is rapidly mutating, long-term cross-species infections have resulted in the accumulation of adaptive mutations and glycosites. Due to the selection pressure of different host immune systems, a disadvantageous mutation would be eliminated while a virus with the gains and losses of glycosites would be conserved.