The people that know me and how I am in the water simply call me "fish."
During water survival training more than twenty years ago, I decided to simply swim to the opposite side of said object, and it took a couple of minutes. The instructors came looking for me, with scuba gear, but I had not yet reached my objective. But it was important due to the scenario with which they presented us. When we surfaced, they chewed me out, I presented my position, and they agreed that while it was a risky choice, given the circumstances, it was the right choice.
That was 1990.
In 2007, a United States Coast Guard Rescue Swimmer (I put that in all-caps because I respect the heck out of what they do. Still, just 9 months ago, one USCG Resque Swimmer (age 26, and I'm nearly two decades older) challenged me to a breath holding contest.
Fine. You're on.
He last something like 2 min 25 sec. I kept going towards three.
What does this prove?
Nothing, other than the fact that some humans have a better, stronger survival instinct (or quite possibly, abilities) than others, regardless of our professions, or ages.
So please explain how it is possible that with my puny 1/10th brain I can locate a dolphin (with my eyes and my puny brain) and at will in a simple getup consisting of a bathing suit and a "stun gun' (12 guage bang charge) go out into the water, literaly bare naked (except for the bathing suit briefs) and come close enough to employ the stun gun against this massively more intelligent being?
Dudes and dudettes, while skin-diving I've placed my hands on dolphines! Wonderful animals.
And please note: I've never done this! I have swum with dolphins, once in their pools (wonderful experience), the rest of the time in their wilds (mostly while body surfing). I would NEVER harm a dolphin.
I've also encountered hammerhead sharks and stone fish (small, but nasty and very deadly little buggers).
My point is this: I define intelligence as to who's at the top of the food chain. Only microbes and virii have been able to get my goat so far, and I've still beaten them!
So, back to the OP: What is intelligence?
I've seen all sorts of "wild" animals from whales to dolphins to chimps to crocs and iguanas exhibit signs of "intelligencel"
Again, I maintain it depends on the species, their capabilities and limitations.
If it were ONLY about "survival of the fittest," that question is easy to answer - simply duck into a shelter, set off a few thousand nukes, emerge a few years later, and wham! Most of life on Earth is dead.
Except for the cockroaches, and I REALLY don't want to be looking towards them as a source of food...