Intelligence is not enough. You can be intelligent without being technological.<p>The dolphin will never make a spacecraft, even if he is twice as smart as we are. Lack of hands is a problem. Also, lack of ability to create fire is a problem. Also, lack of ability to easily pour liquids from one isolated vessel to another, without diluting them is a problem. Basically, no "water worlds" will create a technological civilization, in my opinion.<p>There's also something cultural that may not happen for some reason. Look at the Native Americans. They still didn't have the wheel or metal, four thousand years after others had them. If there is nothing forcing you to develop tech, you won't, even if you're technically smart enough and have the resources that would allow it.<p>I can also imagine some sort of plateau being reached, after a particularly nasty government takes over. What would happen here, if certain countries/groups were suddenly in control of the entire world?<p>We may already be reaching a plateau ourselves. The desire is waning, I think. It has certainly waned in my lifetime, both personally, and as a world, I think. At some point, you become "practical", and decide to expend your time and resources on things closer to home.<p>Add it all up, and it's at least a couple more multipliers for your fermi equation.