Adam Smith famously explained how the division of labor leads to much greater productivity, using the example of the pin factory, where he estimates a 240 and 4800 fold increase in productivity by dividing the labor into several facets. This is like the idea from "I, Pencil", which notes not a single person could completely make a pencil, and this is even more obvious for a product like an iPhone.

 Ever since the invention of farming, productive adults tend to specialize in some economic activity. People are plastic, they can become many different kind of experts, but there's a lot of domain specific knowledge involved in anything so you need to choose a parochial area of expertise at some point. Francis Crick speculates in this lecture that consciousness was basically a by-product of strategic choices like choosing a profession, an interesting thought.

 Most animal thought and most of human instincts are always online, which is why those pictures of danger, sex or food flashed at 100 millisecond intervals affects our affect even though it is all unconscious. Pictures of naked women affect my right, inarticulate, brain because my sex drive is always on, unlike my thoughts about prioritizing research strategies, which takes active thought. Another example is the frog. There is actually a special part of the frog brain that reacts to flying insects, so every frog brain allocates resources towards catching flies.  These online systems are not plastic, and don't allow one to do something else; there can be no frog factory production of fly-burgers for the general pond-frog consumption, which would then free up other frogs to do something different than their ancestors.

 Even in the division of labor within eusocial organisms like ants, different ant phenotypes develop based on the interaction between their genes and their early environment in a deterministic way (see EO Wilson's latest book The Social Conquest of Earth). Bees, dogs, and fish just run on instinct all the time but humans have to choose between being a mason or a farmer, and to make such a comparison involves what we feel as conscious thought and its companions doubt and anxiety (did we make the right choice?). You can't make such a comparison without consciousness, and this goes for all the other choices that must be made in modern societies (Farm what? Irrigate how?).  These aren't instincts, they are learned, and people specialize, forgoing some  areas of knowledge completely and relying on the market to get things where one is incompetent.

 This doesn't seem to pass basic empirical tests.  If consciousness was caused by the the division of labor itself, then pre-literate societies with little division of labor should consist of mainly zombies because their daily routine can be addressed without a lot of questions about whether to do this or that, or at least humans with a significantly reduced level of consciousness. I don't know much about the psychological tests applied to savages but am sure they are not zombies, though I suspect they are not as contemplative as someone from they city.

 I rather think that the division of labor created philosophy. That is, when you choose a profession or some important avocation it supposedly is a better means to an end, but what end? Is it merely to be rich? I doubt that is really so prevalent because to have such a nakedly self-interested goal is not necessarily in the best interest of neighbors, and they would not trust or like such people. As Chris Boehm shows with his work on reverse dominance hierarchies, people hate domination, and generally prefer leaders who consolidate public opinion as opposed to dictate it. The pure selfish motive would not be popular and we are basically social animals, so the best way to project raw selfishness is not your real motive is to actually believe it.

 Thus, we have a lot of existential angst as we try to figure out 'why' we want to build a bridge or have five kids, and it's usually some greater good, not merely one's power and pleasure.  Real satisfaction in life often comes from advancing such higher purposes, imagined though it may be. When we didn't have choices, we didn't have to think about our purpose in life and probably didn't have a philosophy on life. It's unfortunate that modern society creates anxieties that our primitive ancestors did not have simply because they were often acting out of necessity or some inviolable tradition, but developing a healthy purpose in life when you can actually choose is a real advance in the intellectual history of humans. As with most thoughts and philosophies I'm sure your average person's is profoundly ignorant or banal, but still that leaves millions with very enlightened levels of consciousness.

 So, Adam Smith was correct to note the division of labor as a crucial step in human development, but he actually underclubbed it: it didn't just give rise to the industrial revolution, but also to the strange fact that humans think about thinking, meaning, and a sense of self.