Adaptation is where genetic traits are revealed which benefit the organism's survival in a specific environment. Mutation has always given evidence for genetic loss rather than gain. I believe God created this tree and its fruit to better demonstrate His perfect love for us. God gave him dominion over His creation, and clear instruction on this role - but man most definitely was given a directing power over the whole created order. Man was able to reject God's instruction and suffer with ALL creation the consequences of this management decision.
Darkness is really the absence of light, and cold is really the absence of heat.
Evil is really the absence of good. God gave us and apparently the angels a free will. A free will means that we have the ability to choose. We can choose to do that which is good in the sight of God, or we can choose not to, just as we can choose to turn off a light and be in darkness. But the issue of sin as an evolutionary aspect of creation is a little more complicated.