How is it possible that humans are the only intelligent (self-aware) species?

Perhaps every animal has the potential of having cerebrally privileged evolutionary descendants, but on the scale of geological time such paradigm shifting events are spread out because of its low Poisson probability. We won the race (yay, celebrate). If we were to disappear without a trace it could be possible that elephants, chimps, dolphins, or penguins could be the next to hit the cognitive jackpot. Some of them already use tools. But we are where we happen to be in the timeline. The world is ours (for now), and our exponential rise in power - through symbolic abstraction and curiosity and social structure - has engulfed the globe, and as long as we have the power it is highly improbable that any other animal will overtake us. It's like in an RTS game - whoever builds the fastest most efficiently shifts the balance to his almost impenetrable leverage.