That's a question that Eric MacDonald says theists cannot persuasively answer. Prompting his musings was the news that British broadcaster and naturalist David Attenborough - who now says he is an agnostic rather than an atheist - believes evolution is not incompatible with belief in God.
But MacDonald disagrees. He thinks the age-old quest to explain why an all-good and all-powerful God would allow pain to exist (often called theodicy by philosophers and theologians) has reached an insurmountable obstacle with the theory of evolution. As he explains it:
[Darwin] realised, over the years, more and more, that the theory he had discovered was simply inconsistent with the goodness of god, and duck and dive as they please, no one has suggested how to make evolution consistent with a god’s goodness.
But why should this be the case? Current evolutionary theories make four claims that are relevant to theodicy: (1) that life began and then evolved from a common ancestor some 4 billion years, give or take a few hundred million years; (2) that the evolution of lifeless chemical compounds into conscious, rational beings such as ourselves can be explained without reference to God; (3) that the processes by which evolution works (e.g., natural selection, survival of the fittest) have caused a great deal of animal and human suffering; and (4) that these pain-inducing evolutionary processes are a "feature" of evolution - the things that make it all work - rather than a "bug."
The first claim is neutral as to theism. For Christians, perhaps, it's a bit trickier, but most of the confusion surely revolves around the question whether the first 3 chapters of Genesis is a work of poetry and/or myth (albeit a true one, as St. Augustine believed) or a historical account of how God actually created the universe and life on earth. I am with St. Augustine on this, but I do find it interesting that the Genesis creation narratives affirm that life progressed from simpler to more complex species (plant life first, then fish, then birds and so on) finally culminating with human beings, who alone among lifeforms (so far as we know) are able even to ask the question, Where did we come from? This is pretty much what evolution says, too.
The second claim cannot be answered by science unless the god you have in mind is the sort of being who can be detected through the physical senses or, barring that, would have left behind some kind of physical proof of his existence. But so far no scientist has reported looking at a cell through a microscope and seeing a "Made by YHWH" label. Christians, of course, never expected they would. We don't call faith "the evidence of things not seen" for nothing (Hebrews 11:1; KJV). And since we know God is not a physical being, it's no surprise to us that he cannot be perceived the same way physical objects and forces are.
Having said that, the favored atheist explanation for the mystery of how non-living atoms can blindly turn themselves into conscious, rational beings such as ourselves - that it was all a matter of chance occurrences happening over billions and billions of years - actually explains very little. As G.K. Chesterton quipped:
For a man who does not believe in a miracle, a slow miracle would be just as incredible as a swift one. The Greek witch may have turned sailors to swine with a stroke of the wand. But to see a naval gentleman of our acquaintance looking a little more like a pig every day, till he ended up with four trotters and a curly tail would not in any way be more soothing. It might rather be more creepy and uncanny. The medieval wizard may have flown through the air from the top of a tower; but to see an old gentleman walking through the air in a leisurely and lounging manner, would still seem to call for some explanation.
And so it is with the evolutionary explanation of life.
The third and fourth claims of evolution are where the real problems of theodicy arise. But what's interesting is that we have always known both that suffering exists and that it plays an indispensable role in the cycle of life. As any Boy Scout can tell you, some animals kill and eat other animals. And in nature, as on most human farms, this is almost always a violent affair. The weaker animal bleeds, probably experiences pain, and then dies.
But more importantly for our purposes, the weaker animal also gets eaten. First by the stronger animal that killed him, and then by the scavengers, flies, bugs, worms, bacteria and sundry other lifeforms that feed off his carcass. And because of this, the weaker animal's sacrifice, those other lifeforms are able to survive.
Those who ascribe to a Disney-esque view of nature will find all this very troubling. But the prophets of old were under no such delusion. That's why Isaiah's vision of a world where lions eat straw and lie down with lambs in peace is one of a future hope, not an explanation of the world as it is today (though occasionally even now something very much like it happens). In short, Jews and Christians did not need Darwin to know that some animals survive because other animals suffer. Theodicy is thus a problem whether God created each lifeform individually over the course of 6 days or whether he did so through an evolutionary process that lasted billions of years. Either way, suffering is a fact of life. The question that must be answered by theists is whether this suffering can have any redemptive value.
Christians, of course, hope and believe that it can. At the heart of our faith is the suffering, bleeding Christ. His pain was real. But it was not meaningless: God was able to turn Christ's suffering into a supreme good. For our sake, God became the weaker animal, so to speak, and allowed us to kill him. And yet because of this sacrifice, we are now able to find the nourishment we need to survive. Hence the universal invitation, "Take, eat, this is my Body, which is given for you."
But Christ's sacrifice does not just save man. If Paul is to be believed, it will also, in some mysterious way, be the salvation of all creation:
I consider that the sufferings of this present time are not worth comparing with the glory that is to be revealed to us. For the creation waits with eager longing for the revealing of the sons of God; for the creation was subjected to futility, not of its own will but by the will of him who subjected it in hope; because the creation itself will be set free from its bondage to decay and obtain the glorious liberty of the children of God.
We know that the whole creation has been groaning in travail together until now; and not only the creation, but we ourselves, who have the first fruits of the Spirit, groan inwardly as we wait for adoption as sons, the redemption of our bodies. For in this hope we were saved. Now hope that is seen is not hope. For who hopes for what he sees? But if we hope for what we do not see, we wait for it with patience.
Likewise the Spirit helps us in our weakness; for we do not know how to pray as we ought, but the Spirit himself intercedes for us with sighs too deep for words. And he who searches the hearts of men knows what is the mind of the Spirit, because the Spirit intercedes for the saints according to the will of God. We know that in everything God works for good with those who love him, who are called according to his purpose.
(Romans 8:18-28).
This, in a nutshell, is the Christian understanding of suffering. And the first - and perhaps most important - thing to understand about it is that it does not depend on any pretense that suffering is somehow illusory or unimportant. No: suffering is real, it is a basic fact of life, and it is an evil. God promises to help us in our suffering and to one day end it. He does not promise, however, that we will not suffer.
But that's not the end of it. What's new and exciting about the gospel is the hope that God can and will turn our suffering into good just as he did Christ's. And part of that hope is a willingness to see our own suffering as something that is not blind and meaningless - no matter how much it may seem so - but rather as something that can genuinely be sacrificial, and thus beneficial, to ourselves and one another. We have to learn, in other words, to see ourselves in some sense as the weaker animals of nature. Again, here the words of Paul are helpful and suggestive: "Now I rejoice in my sufferings for your sake, and in my flesh I complete what is lacking in Christ's afflictions for the sake of his body, that is, the church" (Colossians 1:24). How our suffering can be united with Christ's and even complete it is a mystery. That it will do so, however, is an article of faith.
Of course, while our belief and hope that all suffering is indeed sacrificial may make our pain easier to bear, it won't make our suffering any less painful. "I thirst," said Christ on the cross. And then: "My God, my God, why have you forsaken me?" If our own Lord could say those things without committing sin, then we can expect no better. His command, after all, was to take up our crosses and follow him. Yet this, too, is the gospel. And those who deny it - those who would promise you an easy answer or an easy way out - are not following the crucified Lord.