An expert system that is expert enough will serve as an intelligence.
The term "intelligence" has always meant "human level". IBM's Watson and his brothers are probably the most advance expert systems on the planet but they lack two key features that make them inferior to humans.
1. They lack the ability to create novel ideas or concepts
2. They lack the ability to make intuitive leaps of logic or to make a conclusion without clearly set parameters aka they lack a "gut".
They also lack emotions but it's debatable if a true AI needs them.
AI still has a long way to go(in a linear apparent sense, not exponential sense), but there are already AI that learn, one of the links I posted names several of them. I certainly think that human intelligence, directed towards a specific task, then employing faster more capable machines on the issue can actually improve on our natural evolution (as it demonstrably has already) to create the human level AI that will have human level abilities...however
, I need to stress such things are not strictly necessary for the Singularity!!