H. PATTEE discussed this ambiguous concept in the following way: "How do we go about determining adaptedness? If a species is well-adapted, does this mean that selection pressures are low and we should not expect rapid evolutionary change? Or is evolutionary creativity an important component of adaptation?" (1972, p.33)
In other words, which one is better adapted: the amoeba, which has survived changeless for hundreds of millions of years by cloning itself, or man, a rather more recent, complex and "efficient" being, but whose future survival is anybody's guess?
In PATTEE's opinion, different criteria of adaptedness should be used at different levels of complexity.