This fascinating piece on animal intelligence adds to the growing body of work suggesting that human intelligence is different from animals only by a matter of "degree, not kind." If we admit that, though, we must also admit that, at least at this point in history, overall human production is different from animals in kind. One way to reconcile these two conclusions is the theory that human intelligence is different precisely in that it facilitates knowledge compounding over time. Just like a small initial difference in an investment can turn into a large difference after many years of compounding interest, so too can an incremental difference in intelligence eventually lead to a vast difference in achievement (for the moment, I'm setting aside the issue of whether this achievement is good or bad).
This line of reasoning, though, could lead one to something like the Singularity: if human abilities are growing exponentially then eventually they reach a near-infinite level. I think this conclusion is largely a fallacy of metaphor. Closer to the truth is that humans compound knowledge at different rates in different domains. The phones in our pockets run as fast as supercomputers did only decades ago, but we've still not put anyone on Mars (or even returned to the Moon, for that matter). Or to use a more mundane example: besides the ubiquity of mobile devices the interiors of homes are largely unchanged over the last 60 years.
Perhaps it is best to say that human ability is an irregular field whose area is monotonically increasing.