>>11534430It conceivable that one of the reason relationship between viruses and cellular life is it's some way beneficial to both as a form of gene transport mechanism. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity similar to sexual reproduction. Viruses reproduce by getting inside your sell and introducing their genetic material and then it uses your cells to make more viruses. However, sometimes that viral insertion fails and it becomes inactive and doesn't make viruses. If that happens to a gamete now you have inactive viral DNA passed to your offspring which can contribute to evolution across generations. This happens rarely but over millions of years this has been accumulated on all jawed vertebrates, and retroviral DNA compromises up to 5-8% of the human genome.
