The catch is we don't know what intelligence is and have no broadly accepted standards to measure intelligence in other animals.
The big headscratcher is in the change that is most widely accepted as the appearance of Homo sapiens sapiens, or Behaviorally Modern Homo sapiens, within a remarkably short span about 50,000 years ago. Within a span of no more than 30,000 years, and mostly confined to a span of 10,000 years, our ancestors began living like humans rather than apes. In Timewalkers, Clive Gamble lists more than a dozen major changes in behavior in the 60,000 to 50,000 ya range.
There have been all sorts of proposed explanations - climate change, a "miracle gene," near extinction in their recent past, space men - for the change. Most of the explanations are plausible (except for the space men) for why it occurred but none (except for the space men) are plausible for why it should wait for 2 million years after Homo habilis started making stone tools. Evolution, in the classical sense, is taunted by this change. It is exceedingly hard to reconcile it with a genetic event.
There is one other factor that almost entirely rules out adaptive evolution. Whatever intelligence is, we have vastly too much of it to credit adaptation. The basis of adaptive evolution theory is that we will randomly develop heritable features that will improve our chances of survival and the individuals with those genes will prevail - in spite of the obvious disagreement with Mendelian genetics. Anyway, that means we should have capabilities that meet our needs: we can run faster than the predators in our habitats or be more fearsome than the ones we can't outrun... things like that. Instead we are one of the most vulnerable large mammals in existence. In spite of that we have mental abilities with no practical purpose as such. We are the only animals that exhibit obvious features of abstract thought, and we carry abstract thought to ridiculous extremes, far beyond anything that makes us better adapted to survival.
We are also probably the most reckless animal that ever lived. In modern times we see people engaging in "extreme sports." For usually no gain people risk serious injury and death. According to Thor Heyerdahl, in order to colonize the paleocontinent of Sahul (now the Australian complex) men and women together must have rafted for days, only knowing those who left before never returned. That is an extreme sport for sure.
In the space of about 30,000 years humans spread from Africa and southern Eurasia to all continents except Antarctica, and now we live there as well... and we have left footprints on the moon. Whatever happened, it is not evolution as we know it. No present day theory provides a satisfactory explanation for what we have done and what we are. That's okay... chimpanzees don't have any theories at all!