You need to read up on ERV's. Science has changed a lot since the 15th century.<quoted text>I was responding to the ridiculous proposal that a virus infected an ancient mammal and inserted a worthless segment of DNA into the host which eventually enabled that host to be able to reproduce. So-called ERV's are nothing of the kind, because they have vital functionality.
from the above link:
"Endogenous retroviruses can play an active role in shaping genomes. Most studies in this area have focused on the genomes of humans and higher primates, but other vertebrates, such as mice and sheep, have also been studied in depth. The long terminal repeat (LTR) sequences that flank ERV genomes frequently act as alternate promoters and enhancers, often contributing to the transcriptome by producing tissue-specific variants. In addition, the retroviral proteins themselves have been co-opted to serve novel host functions, particularly in reproduction and development. Recombination between homologous retroviral sequences has also contributed to gene shuffling and the generation of genetic variation. Furthermore, in the instance of potentially antagonistic effects of retroviral sequences, repressor genes have co-evolved to combat them."