Plagued by stripped attachments and the reasons therefor, I thought I'd never find the solution, but, dummy that I am, at last I did. While I was trying to come up with the relevant variable, which after trailing down dead ends turned out to be subscribing to digest messages, I just had to go look for information on Harlow's attachment theory. I'll never forget the picture of the chicken-wire and terrycloth maternal stand-in with the baby clinging to it. Now there's a book on Harlow and his experiments and their influence: Love at Goon Park: Harry Harlow and the Science of Affection.