Do humans at the upper end of the intelligence spectrum have a greater impact, a lesser impact or an equal impact on world events than those at the lower end of the intelligence spectrum? If the answer is equal or lower, humans have nothing much to worry about should a super-human intelligence show up in the world. Similarly, do humans or any other primate have a stronger influence on world events? If all primates are equal in influence, or if humans aren't at the top, rest easy. Smart brain is to slow brain as (potential) AI is to human. Human is to chimpanzee as (potential) AI is to human. The existing strata suggest future strata.
This is a different question than when or how or whether a super-intelligence might appear.
I agree. My point is merely that super-human intelligence will probably not appear as a sudden surprise.
EDIT: I changed my OP to better reflect what I wanted to say. Thanks!
Claim: The first human-level AIs are not likely to undergo an intelligence explosion.
1) Brains have a ton of computational power: ~86 billion neurons and trillions of connections between them. Unless there's a "shortcut" to intelligence, we won't be able to efficiently simulate a brain for a long time. http://io9.com/this-computer-took-40-minutes-to-simulate-one-second-of-1043288954 describes one of the largest computers in the world simulating 1s of brain activity in 40m (i.e. this "AI" would think 2400 times slower than you or me). The first AIs are not likely to be fast thinkers.
2) Being able to read your own source code does not mean you can self-modify. You know that you're made of DNA. You can even get your own "source code" for a few thousand dollars. No humans have successfully self-modified into an intelligence explosion; the idea seems laughable.
3) Self-improvement is not like compound interest: if an AI comes up with an idea to modify it's source code to make it smarter, that doesn't automatically mean it will have a new idea tomorrow. In fact, as it picks off low-hanging fruit, new ideas will probably be harder and harder to think of. There's no guarantee that "how smart the AI is" will keep up with "how hard it is to think of ways to make the AI smarter"; to me, it seems very unlikely.