In considering the rise and decline of civilisations, nowadays we nearly always seriously underestimate the size of impact which one person can make. At least since Marx, it has been regarded as sophisticated to minimise and explain-away the distinctive contribution of any specific person - to trace all breakthroughs back through their component parts until it seems that things simply organised-themselves without any particular need for humans to take a role.
But it seems likely that original creative thinking is something which very few people can do; and without those very few people it simply does not get done;
The way I think of it is that:
At most a tiny proportion of people sometimes are able to make creative innovations (but in some places, at some times, such people are altogether lacking - and creativity dries-up).
A much larger proportion of people are able to understand innovations once they have been made. Thus a single major innovation can usually, over time, be substantially elaborated, and extrapolated, and improved by 'research and development'.
This extension of an initial breakthrough may unfold over several decades. The unfolding is one possible source of the considerable time-lag in societal change. A society can live-off its past geniuses for a long, long time (depending on the severity of threats it has to face).
And even when understanding has been lost, there are a hundredfold more who can 'operate' the tools and techniques and systems which have been left them by those who understand - and this can further extend the time-lag (although a society which has lost understanding as well as genius is even more vulnerable, more brittle, than the society which has understanding of what-is, but cannot make creative breakthroughs
This came to mind after reading Terryl Given's superb recent book Wrestling the Angel: the foundations of Mormon thought. Mormonism - which is now the religion of some 15 million people around the world, depends almost entirely on one man: Joseph Smith.
Givens make clear on the one hand was an extraordinary achievement came from Joseph Smith - the book of Mormon and other scriptures, the organisation of a new kind of church, an astonishingly radical yet coherent Christian theology - and on the other hand that this was Smith's achievement almost wholly, Smith provided all the major breakthroughs.
Those who followed (Brigham Young, the Pratt brothers etc) had the much. much easier task of organising, selecting and sorting, systematising, adding a little here and taking away a little there. But without Joseph Smith there would have been nothing. So in that sense the whole massive impact of Mormonism is down to a single man.
And the momentum created by that one man is still rolling onwards- even after nearly 200 years - showing the very considerable time-lag of development which often follows the intervention of a Great Man.
Something similar could be said of most major creative geniuses - they certainly did not do everything, nor did they invent everything they used - but without them nothing would have been done; in that sense it is all down to a very few individuals each of very great impact - each of whom was necessary, although not sufficient.
Necessary but not sufficient. No man is an island. The 'understanders' are also needed as well as the creators - but without creators essentially nothing happens except minor twiddling.
There never are very many Great Men, but when there are none - or none in the domains of life where they are most needed - it sets an absolute limit on what can be achieved, or what threats can be resisted.