Alien Genetic Code in Mammals

Viruses can directly write their code in our genes and then that code can make it into offspring?

It is easy to see how point mutations or multiple related mutations in the DNA could happen as part of the reproductive process, but few explanations exist for how the number of base-pairs increases. Without an increase in the base-pairs there isn't more space for coding organism complexity. Perhpas this is a clue?

Or more interestingly, can these viruses dirctly cause a species to evolve or cause speciation?

Science & Technology at Scientific American.com: Viral Gene Appears Crucial to Mammalian Reproduction