Human DNA is >50% Virus DNA?!

[blutoski]

Okay I'm confused... cells created viruses?

Not as a kingdom, but individual viruses could be new, containing host genome by accident instead of the original infection's genome. This is especially likely if there's retrotransposon dna floating around in the nucleus.

 

[BenBurch]

Not as a kingdom, but individual viruses could be new, containing host genome by accident instead of the original infection's genome. This is especially likely if there's retrotransposon dna floating around in the nucleus.

Originally, PERHAPS as a kingdom.

I believe it is likely that the virus came from a strand of naked DNA that escaped from a bacillus that was destroyed in some way, perhaps by over-replication of that bit of mutated DNA. Over time, further mutations brought forth the nucleocapsid and finally the proper virus. Of course conditions would have to be ideal, but there is deep time here.

 

[Skeptic Ginger]

How with this done before we had DNA sequencing?

Just to add to bluto's post, DNA sequencing began in 1975 according to this summary. What changed and what I think has you confused was PCR lab technology and the science of bioinformatics (essentially computer programs that perform biology science data analysis) were more recent developments which have allowed an explosion in data analysis of genomes including sequencing entire genomes of a number of species.