A friend of mine posited that humanity supports itself artificially, and that if that support was interrupted our population would drop drastically to a point where we could subsist on a more basic animal-chewing-on-its-environment level. This idea was rudely dismissed by someone long on education but short on consideration, who insisted that human intelligence renders our race impervious to such cataclysmic indignities. This person needs a brief lesson in how the world actually works.
Mark Twain wrote A Connecticut Yankee in King Arthur's Court
about a modern-day man dropped into the sixth century. This man uses his vast knowledge to give Camelot a crash course on modernization that puts Mao's Great Leap Forward
to shame. The book is primarily a commentary on society, entrenched attitudes, and aristocratic cultures. It's good that it succeeds on that level, because the modernization itself is less plausible than the time travel that proceeds it.
The primary limiting factor on development is not
research or basic understanding, but infrastructure. It's all well and good to know all about electricity, but you need the material. Plain copper wire is a good first step. Obviously, you'll need copper. You can mine it or smelt it, but either way you need people and tools. Then it must be purified, which requires electrolysis, which requires electricity, which is easily produced when you have a water wheel (specialized carpentry)... and purified copper wire. Let's ignore this problem for a moment. Once you have a nice lump of pure copper, you'll need steel for the draw plates (and many of the tools used in processes already mentioned) to stretch the wire; that's another mining process to get the iron, and smelting isn't optional. Getting steel from that iron requires blast furnaces (specialized masonry) and bellows (wood carving, leather working [which requires livestock and tanning industries], and brass [copper and zinc] or bronze [copper and tin]) and charcoal.
By my count, that's a minimum of sixteen developed industries that are required to make a damn piece of copper wire. None of them are optional, even if you're willing to make a very small quantity of low-quality wire. It's worth noting that no one except for the livestock folks are eating what they make, which means that we need agriculture to be developed to the point where it can support not just the farmers but all these non-food-producers as well. And unless all these fields and pastures and mines and smelters and smitheries and forges and crafstmen and forests and charcoal burners and masons and tanneries are all next-door neighbors, we'll need a distribution network of some kind. Yet more tools and toolmakers.
To make it even nastier, even though this industry can all be primitive by our standards, developing it has to be done in baby steps, since so many steps rely on each other in a circular way-- you need better tools to produce the materials to make the tools you need to produce the materials, and so on. Each improvement in a particular process must be small enough to be supported by the processes that come before it, and it must spread and become standard before it can be used as a base to launch improvements in the next step down the line. This is most obvious in the electricity issue above: purifying copper requires purified copper.
This slow, generational process of improvement has more subtle applications than the simply technological. Economic forces drive development. You don't start making a tool until there's a demand for it, and the demand won't develop until the tool exists to support it. Unless you have an omniscient dictator who can feed and shelter his pet industries while they're producing something that's useless at the moment, each step must be a small incremental improvement that has an immediate application. Wiremaking was originally a process exclusive to jewelry-making, and improvements on the process were undertaken to produce finer product more easily. The tools that allowed these process improvements were themselves made possible as a side-effect of constant small improvements in weapon-grade metals, which always had a market. "They were ahead of their time" is a phrase associated with failure, and for good reason.
Speaking of dictators, it's worth mentioning that specialized industry requires a larger population base, which means cities, which means a government stable enough to provide security and rule of law. This is yet another circular, incremental process: government services are supported by a population that relies on government services to survive and prosper enough to support government services. The balance here is every bit as delicate as it is on the economic side; too much organized power tends to crush its populace, and too little tends to let its populace get crushed by someone else who's willing to organize.
Everything about these processes are interconnected, delicate, and ultimately organic. We've seen the process forced in modern times, attempting to jump-start an infrastructure in one underdeveloped region or another. The results range from "humiliating" to "disasterous". Localized segments of industry and agriculture can make Great Leaps Forward, but the lack of a natural support base leads to instability and inevitable collapse. Japan encouraged and accelerated their own development without imposing a planned design, and achieved great success. It still took them a hundred years, even with the ability to lean heavily on the infrastructure of the rest of the developed world.
Steam engines were known to the Greeks 2000 years ago. Schemes for internal combustion predate Da Vinci. There was nothing wrong with their intelligence. Infrastructure. Takes. Time. If our infrastructure were taken away from us, we could probably
recreate it more quickly than it developed the first time (although nothing distracts one from developing metallurgy like starvation, plague, a 40-yr maximum life expectancy, and roving bands of predatory people with goals of their own). On the other hand, we built our infrastructure the first time when metals could be found lying on the surface of the ground, huge forests covered all the continents, and coal and oil could be found in great quantities literally a few dozen meters below the surface.
Humanity's survival at its current level is profoundly artificial. This need not be a criticism. Thousands of years of amazing achievement by individuals and societies have produced a marvelously complex and unthinkably powerful invisible organism whose body exists entirely in the interactions that connect us all. Dismissing its creation as a simple symptom of "intelligence" is arrogant and idiotic. Taking its existence for granted is suicidal.