Augustine calls evil the “privation of a good” (Confessions Book 3 Chapter 7).
Good and evil are similar to light and darkness. Darkness isn’t a “thing” but the absence of light.
You appeal to science as revealing false the belief that we descended from Adam and Eve. You are entitled to this bare assertion but it is ironic that you turn around and talk about the evil of millions of years of animal suffering. What’s evil about animal suffering from the scientific standpoint? Isn’t it ultimately indifferent?
As you have indicated, Christians have a framework (whether or not you agree with it) for understanding what is good and what is evil.
What is your framework for believing in good and evil?
Ravi Zacharias helpfully explains,
“Some time ago I was speaking at a university in England, when a rather exasperated person in the audience made his attack upon God.
"There cannot possibly be a God," he said, "with all the evil and suffering that exists in the world!"
I asked, "When you say there is such a thing as evil, are you not assuming that there is such a thing as good?"
"Of course," he retorted.
"But when you assume there is such a thing as good, are you not also assuming that there is such a thing as a moral law on the basis of which to distinguish between good and evil?"
"I suppose so," came the hesitant and much softer reply.
"If, then, there is a moral law," I said, "you must also posit a moral law giver. But that is who you are trying to disprove and not prove. If there is no transcendent moral law giver, there is no absolute moral law. If there is no moral law, there really is no good. If there is no good there is no evil. I am not sure what your question is!"
There was silence and then he said, "What, then, am I asking you?"
He was visibly jolted that at the heart of his question lay an assumption that contradicted his own conclusion.
You see friends, the skeptic not only has to give an answer to his or her own question, but also has to justify the question itself. And even as the laughter subsided I reminded him that his question was indeed reasonable, but that his question justified my assumption that this was a moral universe. For if God is not the author of life, neither good nor bad are meaningful terms.”
The Christian “answer” to the problem of evil is not ultimately found in syllogism or equation but the Person and work of Jesus Christ. As the philosopher Peter John Kreeft put it, “Many Christians try to get God off the hook for suffering; God put himself on the hook, so to speak – on the cross.”