Radiolab delved into this a bit in their show "Parasites" from a while back. You can listen to the relevant segment under "The Scratch", although I recommend th

Radiolab delved into this a bit in their show "Parasites" from a while back. You can listen to the relevant segment under "The Scratch", although I recommend the whole thing, of course: http://www.radiolab.org/2009/sep/07/ http://www.radiolab.org/2009/sep/07/