People take their religion very seriously but seldom are capable of following the rules and regulations of the belief.
It's not that people take religion very seriously, it's that religion is reality in their minds. Things can be very real in the minds of people, but be completely absent in the universe itself or in the minds of others. As to what it means to believe, it is exactly that - but I find often people put in their own interpretations which are not communicated trough religious texts.
Science can not explain everything, hence people need to find rational explanation on things they can not understand and find religion.
The believe in evolution is not that much different than the believe in god, both are highly speculative with no concrete proof.