1. A method for evaluating a condition of an engine, the method comprising: obtaining a sample signature of a first engine, the sample signature characterizing the first engine as a function of a fluid sample of the first engine; comparing the sample signature to a plurality of reference signatures obtained from reference engines belonging to a common family with the first engine; selecting ones of the reference engines for which a difference between a corresponding reference signature and the sample signature is below a threshold; and providing historical engine data of the selected ones of the reference engines as a basis for evaluating the condition of the first engine.