It's worth remembering in the case of discoveries like this that the oldest instance of the practice is almost certainly far older than the oldest preserved instance of the practice.<p>Unfortunately, there has been relatively little statistical work done to use distributions of preserved ages to infer the age of origin, and although I recall reading an article in Nature on the problem in the '80's or early '90's it would seem that most of the people working in the field have not really focused on this problem, and instead continue to apply a mixture of "The practice began around the time of the earliest preserved instance of it" and "The practice began earlier by some amount that I will estimate from my gut".<p>Neither of these is approaches is methodologically sound, and both tend to underestimate the ultimate age of a given practice (or species, in the case of fossils) and tend to underestimate the error bars as well.