Your statement, and its implications are a false tautology. It says, because it exists and because it is part of nature then it is possible and nature did it. This is a complete fallacy. There is no goal in chaos. There is no purpose in it. There is however a goal and a purpose in a gene. It needs to function, to do something which is not being done already by another gene, and to do it better than it is being done already. You cannot achieve that by random chance.
"False tautology?" A rose is not a rose? (Tautologies are never false.) You're just bandying the words about meaninglessly here. Forget arguing C vs E. Take a logic class, or elementary geometry.
No, there isn't. A gene just happens to be. If it's beneficial to the animal then the chances are high that it's passed on. OTH if it's detrimental to that particular organism then this organism is less likely to survive and pass it on.
It's trial and error. Whether a gene is good or bad is only kown after it exists and is 'tested' by the environmental conditions.