Octopi indeed:

The Aquarium had an octopus expert, Roland Anderson, answering questions, so I soon asked him the one that has been bothering me. Among mammals and birds, the smartest are social, long lived, and have few children. Octopuses may be the smartest invertebrate, and they are asocial, short lived, and have many children. (If I caught one of the talks right, Sappho will be looking forward to somewhere between 60,000 and 80,000 blessed events.) So, my question was: Why are octopuses so smart? Part of the answer is that they are not terribly smart, perhaps as smart as a rat, rather than a crow or monkey. For the rest, no one really seems to know, though some think that octopuses may have traded a shell for smarts millons of years ago.

The nice thing about evolution is that, as the old joke goes, we don't have to outrun the bear, we just have to outrun you. With "the bear" being perfection and "you" being the next species over, if that wasn't clear. To people who ask, Why this way and not another, the answer is usually, Well, then we'd be [species X], which does do things that way. It's just got to work; it doesn't have to be pretty.

Via the incomparable Natalie Solent.