Interestingly according to etymonline, it comes from the same group as “think” so thanking essentially means to give good thoughts and gratitude. In French, the translation of thanks is “merci”, which is like mercy, to spare someone.
At the time these words started to be used, we had no way to publicize “good thoughts” beyond the parties to a transaction or a family or village, but today we have the Web.
If we think about the Web version of the “thanks”, it would essentially be a written statement of gratitude for something you’ve received, possibly because you didn’t have to sacrifice anything to obtain it, or because your sacrifice in the exchange was much smaller than the other party.
These “thanks” could be aggregated in a PageRank-like “ThankRank”, which would be quite useful when we want to decide where to direct our own generosity.