This is actually under debate. There is disagreement among neuroscientists whether intelligence is a result of brain modularity (specific regions of the brains

This is actually under debate. There is disagreement among neuroscientists whether intelligence is a result of brain modularity (specific regions of the brains optimized for certain tasks), or due to brain size alone. All that said, I'm skeptical of the singularity since it assumes that a recursive process can continually improve intelligence without significant diminishing returns. The problem with this thinking is that it fails to take into account evolution. All this research into AI is based on the assumption that "intelligence" should be like human intelligence. But human intelligence has had several billion years to evolve and is highly optimized for our environment (actually our environment from several tens of thousands of years ago when we were hunter gatherers). It seems naive to me to assume that we are not nearing a local optimum in what is possible with human intelligence. I don't believe a singularity is possible because by recursively improving "intelligence" you will near the local optimum of that form of intelligence but that does not mean you can continue improving that intelligence indefinitely.