for the discipline and the personal and professional courage to risk the firm niche he had already carved for himself in sociological theory over the past generation. It is rather to say that, even if his " reading " of the past were relatively correct, his conviction that " though major changes are in process, the sociologist of the twenty-first century will discern just as many factors of continuity with the past as we can now discern with the twentieth century, and, of course, those previous to it " (Parsons, 1971a, pp. 142-3) and his assignment of the United States as the new " lead " society for that future will almost certainly elicit a major articulation or a series of ad hoc modifications from him (or from those others who have identified with its fundamental outline) if his sketch and his claim is to survive much beyond his lifetime (or theirs). The S-curve What is it in the panorama that he has painted that appears potentially dated? To be anything but modest, I would claim to begin with that the originai " dynamic " with which he worked, resurrected from Spencer and read by Parsons from the ambiguous record of biological evolution to date, is itself subject to serious question. That energizing principle? The assumption that increasing differentiation of function necessarily contributes to " increased adaptive capacity "• (Parsons, 1966, pp. 22-5). It should be noted that Parsons himself (1971a, pp. 36-40) recognizes the break even in the West that the early Middle Ages represented in the overall contribution of functional differentiation to " increased adaptive capacity ". Thus, there is nothing in principle which would restrain him from modifying in his future work the linear manner in which he projects twentieth century increases in differentiation of function into the twenty-first. But what is it that might serve as a contemporary surrogate to the anomaly regarding the direction taken by functional differentiation in the Dark Ages? Curiously the answer lies in Parsons' apparent blindness — at least through 1971 — to a feature of living systems that one who relies as heavily upon organicist analogies as Parsons would not be expected to have overlooked. It is, very simply stated, its S-curve nature. Almost ali forms of organic life grow relatively slowly at first; this is typically followed by an exponential burst; finally, with maturity, growth plateaus. Indeed, in most cases, the regenerative process is overtaken by processes of degeneration long before the life cycle has completed itself. If the S-curve had not been applied with a measure of success to develop- ments within human society, one might admire Parsons' hesitation to push his organic imagery this far. But its application to societal factors has indeed 51