The ultimate and most ancient point system for "quantizing success through a numerical method" is, of course, money. Or perhaps predating even that, number of cattle, sheep, size of land controlled, etc. And war and trade were very early human activities to optimize that quantized success.
History aside, LordVreeg's answer above looks the most promising to me so far in terms of modern gaming.
Update
Since my original post, I have found a online-viewable citation that clearly credits David Arneson (co-creator of D&D with Gary Gygax) as creator of the "experience (point) system". It comes from a March 2008 Wired Magazine article, "Dungeon Master: The Life and Legacy of Gary Gygax" by David Kushner, and was written shortly after Gygax died (2008). It describes the creation/development/motivation of the experience point system this way:
Arneson tested his Chainmail mod in play sessions with his group and, based on their feedback, continued to tinker with the rules to make it more fun. ...
There was another aspect of the game he wanted to tweak: the fact that it ended. Arneson's group was having too much fun playing these specific roles to want to part with them after a single game. Outside of the individual games, Arneson created an experience system for characters. Your character would earn experience points based on their success from game to game. After a certain number of poins [sic], a character would "level up."
It does seem to be clear from this point that experience points were not in Chainmail and were Arneson's invention and part of his contribution to D&D. It does not necessarily rule in or out whether Areneson pulled the idea from somewhere else however.
Your question and other comments do leave me curious to know about ancient competitions (e.g. gladiators, tournaments such as jousting tournaments)-- whether they had any cumulative or longer-term rankings (based on win/loss ratios or #wins) that would be quantitative and cumulative in nature and thus similar to XP beyond what you'd just find in "sports".
I think it's a great topic worthy of intellectual and historical research. What you call "currency of achievement" is what I think of as a "Cumulative point system". As I've reflected upon my own behavior and others' over time, and beyond just the sphere of "games", I've found that cumulative point systems-- whether found in games, online forum reputation systems, or real-world systems like money -- tend to have three great virtues that make them addictive-behavior generating:
- immediate feedback (delayed feedback
reduces addictiveness)
- clearly recognizable feedback (quantization
adds clarity that increases
addictiveness)
- effort compounds over
time (benefits that last into the indefinite future are much more valuable than transient ones, increasing addictiveness)
Good luck with your research!
If the EXP system isn't working for you, throw it out all together and hand out levels as you see fit. This can be done after x number of sessions or after some in game adventuring milestone.
My group has done this for a while and have never had a problem.
Pathfinder eliminated XP costs that DnD3.5 had so the only time XP is an issue will be when the party is of mixed levels (which is something I try not to have in the first place).
Best Answer
Really, experience points are just a game mechanic, used to incentivize and/or reward certain behaviors
As noted in the passage you quoted, they are meant as rough indicators of the experiences that help a character learn, grow, and improve herself...but any close mapping to how real people learn and grow is tenuous at best.
Would apprenticing with a high level wizard help you master new spells as quickly as shooting orcs with magic missiles day after day? Perhaps, but it wouldn't make for an interesting game incentive.
Some GMs assign XP only (or primarily) for defeating monsters. Others use them to reward clever solutions to problems and/or great roleplaying. In either case, looking too closely reveals that XP are really just a means to incentivize and/or reward certain behaviors.
Pathfinder without XP
As a side note, at least half the Pathfinder (and other 3.x) games I play nowadays don't actually use them; the party just levels up when it fits the story.
In general, I'm a fan of doing away with XP in Pathfinder, but there are downsides to doing so. The main advantages I see of using XP versus simply leveling by GM fiat are: