Because in truth, had there been no Gutenberg, the printing press would have been discovered in (or imported to) Europe - eventually. Would it have been five years later? 10 years later? 100 years later? Impossible to know. But, we should think, eventually, it would have been.

Yet there are interesting cases from history. We know of five different modes of human stone tool-making that pre-date the Neolithic (the New Stone Age). They are:

The Oldowan Industry. Simple core form rocks, used for things like chopping. Oldowan tools emerged 2.6 million years ago, devised by either Homo habilis or Homo erectus in Northern Africa.

The Acheulean Industry. Biface rock tools, with more complex design than Oldowan tools. The axe is the most notable example of this type of tool. Acheulean tools first date to 1.76 million years ago, devised by Homo erectus in Western and Southern Africa.

The Mousterian Industry. Fine-pointed rock tools that may have relied on greater grip strength to create. Mousterian tools date to 315,000 years ago, devised by Neanderthal man in Europe.

The Aurignacian Industry. Fine bladed stone tools, along with worked bone and antler points, struck from prepared cores rather than crude flakes. Aurignacian tools have been found throughout Europe and the Levant, and are believed to have emerged in the Levant around 43,000 years ago.

The Microlithic Industry. Microliths were small stones used in composite tools, fastened to a haft. They were devised in Europe and the Levant about 35,000 years ago.

Now here's something to think about.

We know how invention works. It is rarely (or never) collaborative across an entire society; an entire society does not invent something. Instead, one man comes up with an idea, and either builds it himself, or sets off a chain of competitors who race to be the first to build the thing (in which case you have the collaboration of the guy who proposes the idea, a few guys who try to build it, and one or more who actually succeeds).

Essentially though, you can boil the invention down to a handful of people. The guy who thinks it up, and maybe a few other guys who devise it and refine it (if the original idea guy doesn't do all that himself - and he may).

So, now. At some point, 2.6 million years ago, some human started to make simple rock tools. He taught it to his tribemates, and perhaps some of them helped to refine his designs.

No one came up with a new design for nearly one million years.

Or, if anyone did, he didn't share his design with others, or it never caught on. Because the tool industry did not change for 840 milenia

Finally, 1.76 million years ago, some other human figured out how to make biface rock tools. And he taught it to his tribemates, and maybe they refined how these were made a bit too.

Acheulean tools. Might look simple, but it took our ancestors 840,000 years to come up with these.

This time, no one came up with another new design for 1.3 million years!

So here's a question. If you took a time machine back and found that one guy who figured out how to make bifaced tools 1.76 million years ago, and you assassinated that guy before he came up with those tools... what happens?

When is the next guy born who figures this out?

100,000 years later? 200,000 years later?

It took 840,000 years for this guy to be born after the invention of the Oldowan Industry. And another inventor like him did not show up for another 1.3 million years, when the Mousterian Industry was set up. That's one great inventor every one million years or so. Go back in time and take one of those men out, and how long do you have to wait for society to produce another inventor?

We have one example of the time lag between invention: the Neolithic Tool Industry.

The Japanese figured out how to make ground stone tools (key tools of the Neolithic) 40,000 years ago; the Chinese had Neolithic pottery 20,000 years ago. It took the people of the West (in this case, the Fertile Crescent) a further 28,000 years after Japan to figure this out - they did not go Neolithic until 12,000 years ago. Europeans, North Africans, and South Asians entered the Neolithic around 9,000 years ago. The Native Americans, the Inuit, sub-Saharan Africans, and Australian Aborigines never went Neolithic, and instead leap frogged to later technology after trading and European colonization.

Japan had Neolithic tools 40,000 years ago. The next closest (China) took a further 20,000 years to get there (and may well have received it from Japanese immigration or a Chinese expedition to Japan). Everyone else took even longer (and again, the technology may simple have spread West from Japan - that is one possible explanation why Native Americans, Australian Aborigines, and sub-Saharan Africans never went Neolithic - the technology never crossed the oceans or the desert).

That's the quantifiable impact of one man: 20,000 or more years.

If that Japanese guy - name lost to history - who put the key parts of the Japanese Neolithic tool industry in place died in infancy, Japan may have had to wait until 20,000 years later (or more) before it discovered these tools. Perhaps.

Maybe there were conditions in place that made it more likely someone would discover Neolithic tools 20,000 years earlier than anyone else in Japan. Perhaps that particular inventor's tribe had some sort of way of living that made it easier to discover, or made it more necessary to discover, tools like these.

But just as likely is that this was just some lone, crazy guy - like many inventors are - who went off in a cave somewhere with some nutty idea that most people told him was insane, and came back with the next evolutionary step in tool construction... 20,000 years sooner than anybody else.

The great man theory is set up against 'history from below', the other theory we discussed, where great men are mere vehicles for the impulses of their societies.

Yet, as William James points out, there is no reason, need, or sense to be an absolutist about these. Great men are shaped by their societies, and shape their societies in turn.

A great man is the product of his society. Yet, he alters the destiny of his society too.

All men play their individual roles in nudging their society this way or that way. Men who accumulate more power, or act in outsize ways, are able to give their societies (and others they come into contact with) bigger nudges.

What direction do men nudge their societies in? This is impacted by all sorts of things, including the man's inherited personality characteristics, his learned/developed personality characteristics, personal (and especially childhood) experiences, the role models he's taken to, and the skills he has developed over time, as well as the opportunities presented or not presented to him. And of course it is impacted in a big way by what stage of the civilizational lifestyle the society he is born into is in, and what the overall environment of that society might be.

It is silly to suggest great men operate in isolation upon the levers of history - just as it is to suggest great men do not matter and history charts the path it would chart whether any individual man lived or not.