Viruses can cause diseases, but their more important role is as drivers of evolution. They may have contributed to the origin of life as noncoding RNA, which we know today from viroids and ribozymes. Viroids/ribozymes are the most ancient entities that can replicate and evolve. They may have been autonomous, helping build up larger structures, protocells, and cells. An often underestimated trend in evolution is loss of function (LoF) in contrast to gain of function (GoF). For the simplest virus, phage Qbeta, gene loss allows an increased speed of replication in vitro (Spiegelman’s Monster). The model of how genes may have evolved has been designed by M. Eigen with his hypercycle, which can be applied to RNA only and reduces the almost infinite possibilities of sequences to realistic numbers. Retroviruses with and without deletions and, to a lesser extent, other viruses, accumulated in the human and other genomes, where they contributed to new properties such as, allowing embryonic growth inside the uterus. Viruses are active in horizontal gene transfer; they can transport gene regulators and recombine with growth-promoting genes such as oncogenes. Many of them are the strongest cancer genes we know of. Transposable elements are important for gene modifications and can be defined as endogenous rudimentary viruses lacking coats. RNA viral diseases are models for evolution in time-lapse. Viruses introduced immunity into their host cells. Many properties of viruses resemble social traits that are reminiscent of the social behavior of all living species.