system
Given the following post, respond as if you're commenting on Reddit:
human
How did viral DNA become part of the human genome?

There are some answers discussing how it was detected, or what they do, but none touch the topic of how viruses become part of our DNA. Specifically by what mechanism can anything external get integrated in anyone else dna?
gpt
The life cycle of a virus goes as follows. A virus attaches to their specific host, then inject their genetic material into the host. The host then gets "fooled" into reading this material and making more and more viruses. Once there's so many viruses that the host can no longer perform the function to keep itself alive, it essentially explodes and releases the next generation of viruses into the world. 

Viruses can copy their DNA into their host for this purposes, but sometimes the virus is over powered or the cell survives infection and the genetic material the virus input is kept. If this happens in a gamete (sperm or egg cell) that goes on to be fertilized, that viral input is copied from the gamete to every daughter cell and voila, you have inserted viral genes into a multicellular organism.