The other great apes are quite intelligent and occupy the top spots in their ecological niches. Bottlenose dolphins pass the mirror test for self-awareness and appear to have individual names [1], and are at the top of their ecological niche. Elephants pass the mirror test and are at the top of their ecological niche. Octopuses are surprisingly intelligent for invertebrates, and are among the top predators in their niches. In the blink of an ecological eye, intelligence has started showing up at the top spots of the food chain across a diversity of different niches. Just because we haven't seen it before (e.g., the top dinosaur intelligence, the genus Troodon, only had a brain-to-body mass ratio comparable to modern birds [2]), doesn't mean it isn't adaptive - only that it took a while to evolve. Life existed for a pretty long time on Earth before it started running around on the land, too. Doesn't mean running around on the land is maladaptive.
[1] http://www.wired.com/wiredscience/2013/02/dolphin-names/ [2] http://en.wikipedia.org/wiki/Troodon