Here's a definition-hypothesis. Intelligence is a complex instinct which hasn't yet fully matured. The idea is that instinctive activity is always natural and useful. A million years will pass, the instinct will mature, and we will cease making the mistakes which are probably an integral part of intelligence. And then, if anything in the universe changes, we will happily become extinct - again, precisely because we've lost the art of making mistakes, that is, trying various things not prescribed by a rigid code.
~ Dr Valentine Pilman