I had a game a long time ago (when I first started playing on prince) on pangea with about 14 civs (large map). Somehow this game I was friends with nearly everyone but the usual suspects (Tokugawa, Montezuma, Isabella). And by that, I really mean everyone loved me, I had pleased and friendly with them all. Anyway, I had a pretty poor start and all my resources were on the edge of my empire next to Tokugawa. I had been playing too peacably and Tokugawa kept invading. After repelling him many times, Alexander saw my weakness too and invaded, followed by Julius Ceasar and Napoleon. The first city Alexander took with his endless swarm of Elephants was my city with both iron and horses. Needless to say, I was screwed for this game, but I decided to play it out and try to survive. Long story short, I sued for peace and was left with one city. I played this out for a long time (100 more turns or so, they went fast with nothing to do). And I fell farther and farther behind in tech and power and culture and points. Then, my good friends from before, much to my amazement, began showing up and giving me old techs I had never bothered to research. Within 10 turns, three civs (Hepshutsep, Qin, and Roosevelt) all stopped by and dropped off old techs (Currency, Compass, and Philosophy, I think). I think after a tech is completely worthless, and the computer no longer sees you as a threat, they will "help you out" by giving you the tech if you're Friendly or highly Pleased. At least that's my experience with it.