In order for an intelligence to be called general it would be necessary to be effective in all situations. Humans only perceive the world through our five limited senses and then filters it through the coloured glass of our concepts. We can't escape the limitations of our senses and mental models taken together.
Humans can't even keep in the working memory more than 7 objects at once, some people can handle a few more but not on the order of hundreds or thousands. What if the real ultimate theory of physics required a working memory of 1000 objects? We'd be forever blocked from grasping it like an ant vs. the stock-market. Programmers live at the edge of this grasping power and know the horror of not being able to take it all in at once, and it's so easy to get into such a situation.
It is possible that there is no general intelligence anywhere. It's always an intelligence of a specific environment, solving specific types of problems. A general intelligence would need a much more varied and challenging environment in order to reach that level of intelligence.
The more complex the environment, the higher the intelligence of its agents. So there is always going to be an upper limit to intelligence, and the environment has a lot to do with it. No intelligence is truly general.