FRAGMENT FROM NATURE focuses for this and next weekend on the work of Professor Lluis Villarreal, who has proposed that viruses have played an intimate role in human evolution, and all major evolutionary transitions. He has been an outspoken and sometimes controversial voice for this biological dark matter at a time when most biologists dismiss viruses as oddball curiosities that are more chemical than living. They have left their traces in our genomes, have fashioned some of the great cycles on this planet, defy species limits, and outnumber other creatures. Enjoy this glimpse into biological dark matter that is mostly left in the biological rubbish bin.