I saw this image on Facebook the other day (states "God isn't an option, He's a necessity"). As a Christian I accept this because it is a part of the truth of Christianity (and consequently, reality). But the unbeliever doesn't tend to accept it or even appreciate the significance of this statement...especially if they claim to
know anything (even as minimal as that they exist). Formally put, here is one way to present the argument:
1. Evolution is driven by survivability of organisms
2. Human brains and senses are the product of evolution
3. Therefore human brains' and senses' existence is driven by survivability- From 1 and 2
4. Beliefs come from the human brain reacting to sense experience
5. Therefore beliefs exist based on assistance to survivability- From 3 and 4
6. Humans believe that God exists
7. Therefore the belief that God exists exists based on its assistance to survivability- From 5 and 6
8. God does not exist
9. Therefore evolution favors false beliefs over true beliefs if the false belief helps survivability more than the true belief- From 7 and 8
10. Therefore the human brain and senses cannot be trusted to yield truth about reality (knowledge)- From 2 and 9