Viruses are strange things that are not quite living, but not quite non-living either. 

They are bits of RNA or DNA that are enclosed in a protein shell and require a host to survive and replicate. 

So where did they come from, how long have they been here and why do they keep hanging around? 

Find the answers to these questions and much more in this very interesting video by PBS Eons. 

Don't forget to leave a comment below to let me know what you thought about the video!