Human Evolution & Its stages

I was reading the evolution of human. Well, I noticed a trend ( which I think is the most important aspect of human evolution) is the increasing cranial capacity. The capacity gradually increased and thus more intelligent , skilled, efficient ancestors of human were formed.
But the most recent direct ancestor of modern human i.e. Cro-magnon man ( Homo sapiens fossilis) had more cranial capacity (~1650 cc) than modern human (1300-1600 cc).
The trend in evolution tells that the cranial capacity for modern man should have been more than Cro-magnon man. Let's assume that it might have been remained the same.
But why the cranial capacity decreased??
Evolution always helps to form greater & advanced species.
But in this case if we consider the cranial capacity, it seemes that our ancestors were more intelligent and cultured than us. HOW IS THAT EVEN POSSIBLE??
And if my assertion is wrong than at least explain me why the capacity decreased?
So in the end my questions are---
1. WERE CRO-MAGNON MEN MORE ADVANCED THAN HOMO SAPIENS SAPIENS?
2. WHY THE CRANIAL CAPACITY DECREASED DEFYING THE LAWS OF EVOLUTION?