Classic pure-bred evolutionary theory (Richard Dawson style) says evolution is pure random walk with no bias towards intelligence or anything else. It's simply genetic information seeking to propagate more and more of itself.

Recently, others have hypothethized "complexity theory" a paradigm that says there is evidence for factors, yet unknown laws, that force the arrow of chemical and biological evolution to more and more complex systems with intelligence as an example of complexity. Philosophically I would prefer this to be so. The supporting evidence so far is scanty and mostly in the form of just so hidesight. But so is our knowlege.

-philw