Life has its problems. To succeed it has to survive: to survive it has to sacrifice its identity. And viruses have their fingers in the essence of it all. Consider the situation. There are useful genes. Such genes promote the survival of the individuals which house them. It is not unreasonable, therefore, to expect that an enterprising life-form would seek to gain advantage from the existence of such useful genes by distributing them around the life forms which are not so blessed. This achieves two effects. It justifies the existence of a class of organisms which serve as gene transporters (vectors) and it provides the recipient with benefit (a situation from which the transporter can also gain). Of course, the system can have its teething troubles as in the case of the transporter that provides a package which does damage and thereby decreases the survival of both the recipient and its invader. Yet, over a billion or so years, organisms of increasing complexity have emerged owing not a little to the processes of whole gene transfer by vector systems.