Fusion proteins in one species have fusion components in yet another species. The evolutionary relationship between fused proteins and fusion components is interesting. A number of such cases have been documented in the literature. The fused proteins in one species mimic important phenomena such as operon-like structures, protein subunit interaction, multiple functionalities, and alternative splicing in another species. These observable facts are discussed using suitable examples. The significance of fusion proteins in molecular evolution is discussed by structures with known fused/unfused architectures and by probing their variability during simulation.