Interesting task assignment.
Okay, first to be intelligent, you have to be self aware. So, prerequisite: Consciousness
That given: The ability to assimilate input in such a manner that it ensures that reaction to further input will be that which promotes subjective goodness. (note that survival is implicit, along with 'bad' can be good subjectively) The greater the ability to promote the subjective goodness, the greater the intellect.
To put it far more strangely: The more of your subjective experience (past, present and estimated future) you can be aware of at any point in time (the present), the more intelligent you are. In essence - you're smart if you live in a big old bubble of subjective time (compared to the intellects that is).
I guess that enables people to make keen observations. So I guess that means that what I described above is only the potential for free will. One still needs some type of motivation or ability to see into that 'bubble of time' before intellegence is establshed.
Eh, at least that's my stab at it for now.