It would seem that the thing that has made us powerful is our ability to build on past advances. The ability to create something that not only survives our deaths, but indeed had nothing to do with our lives to begin with. Knowledge isn't a fundamental property of humanity, but a propensity to build on it is.
Our advantage is the joint ability to create and communicate knowledge. But at the same, it should be noted that neither invention nor communication are the exclusive territory of humanity. Perhaps there is a threshold of ability, above which learning accelerates, and below which learning stagnates.
There was an interesting diversity of responses including things like "the encapsulation and expression of priorities" (Nice, Bob. row 6), selflessness, tools, long distance running (interesting! row 10), persistence, and behavioral flexibility.
By far the most common response was language. My opinion is that language is closely related to our greatest strength, but that is not much of a strength itself. (Besides, language often leads to problems because of the illusion that communication has taken place.) In some of your articulations of why language matters, I think you identified what really matters. Bob (row 6) called it "effective collaboration" and row 12 called it "institutional intelligence". I call it "collective intelligence", and define it broadly as groups of individuals doing things collectively that seem intelligent. (Definition stolen from an interesting paper called Harnessing Crowds.)
To try to be less abstract and hand wavey, I see the primary components of collective intelligence as coordination and cooperation, the division of labor, and collective cognition. Collective intelligence is mostly the product of our ultra-sociality, a trait we share with ants, bees, wasps, termites, and only one other mammal: naked mole rats. Judging by the relative "success" of these species, ultra-sociality appears to be highly adaptive. Toss in the capacity for language, reasoning, abstract thought, empathy, intentionality, love & compassion, and future-mindedness & goal-setting and you begin to see the recipe that has made humans so powerful. While all of these factors matter, they would be considerably less valuable without the foundation of ultra-sociality / collective intelligence.
Collective intelligence is apparent in the almost magical series of events that takes place in a market system. For a beautiful illustration, read Leonard Read's essay I, Pencil, a work that has become a sort of Libertarian manifesto. The essence is that no man can create even a simple pencil by himself -- it requires the coordinated effort of countless individuals, the division of labor, and a price system.
I believe the internet's greatest potential lies in the ability to harness collective intelligence. More on that soon, I hope.
