If you ever find yourself in a debate with William Lane Craig and try to use evolution as evidence for naturalism, you can expect him to make the following counter argument below. He's made it in several debates now and it's become one of his all-too-often repeated talking points. This one is transcribed from his debate with Peter Atkins from way back in the 90s:
In their book, The Anthropic Cosmological Principle, Barrow and Tipler lay out 10 steps necessary to the course of human evolution, each of which, each of which is so improbable, that before it would occur the sun would have ceased to be a main sequence star and would have burned up the earth. Now it seems to me that if evolution did occur, then it would have had to been a miracle. In other words evolution is literally evidence for the existence of god!
That's right creationists, evolution now is evidence for the existence of god, so stop denying it and embrace full on macroevolution. (Sigh) Craig wants to be able to deny Darwinian evolution and instead support a sort of hybrid old earth creationism/theistic evolution, but just in case that becomes too much of an untenable position, he's carefully made naturalistic macroevolution safe for Christians because it's a "miracle."
So I wonder, is Craig blissfully unaware that everything that happens in our universe is improbable? Every single person born is improbable if we were to try to calculate the mathematical odds of any of us being born. For example, the average man will make about 4.3 trillion sperm cells in his life (200 million per day on average for ~60 years). The only way you could have been born is by a single sperm cell from your father, and a single egg from your mother. Right there the odds of you being born are at least 4.3 trillion to one, or 1 in 4.3 x 1012.
But according to Robin Baker, who wrote the 1996 book, Sperm Wars, only about 1 percent of the sperm cells a man produces actually are involved in fertilizing eggs. These are what he calls, "egg-getters." Most of the other 99 percent of sperm cells are designed to kill off sperm from other men. So if we recalculate, 1 percent of 4.3 trillion is 43 billion. That leaves the odds of you being born from your father at 1 in 43 billion. Not exactly odds you'd want to bet your money on.
For most men the rate of sperm production decreases with age, so let's round that down to about 36 billion egg-getter sperm cells over the average man's lifetime. The average man will have about 2-3 surviving offspring during his lifetime, if we round up to 3, the average chances of you being born are 3 x 1 / 3.6 x 1010 or 1 / 1.2 x 1010. That's 1 in 12 billion, slightly better than before but remember we're only going back one generation.
If you include two generations, your dad and his dad, the odds of you being born will be 1 /12,000,000,000 x 1 / 12,000,000,000 = 1 / 144,000,000,000,000,000,000 or 1 in 144,000,000,000,000,000,000 or 1 / 1.44 x 1020. That's 1 in 144 quintillion in just two generations.
To calculate the odds for 10 generations that would get you (1 / 1.2 x 1010)10 = 1 / 6 x 10100. That's a 6 with one hundred zeros after it. And we've only gone back 10 generations! To give you a sense of how large that number is, the total number of atoms in the universe is estimated at just 1080 which is far lower that the odds of just you being born going back only 10 generations.
Continuing with these odds, if we went back 1 million years or roughly 40,000 generations (where each generation is considered 25 years), the chances of you being born is at most 1 in 1.8 x 10403167 or an 18 with 403,167 zeros after the 1*. That's more than the number of atoms in the universe if each atom in the universe contained as many atoms as the entire universe! It's simply an astronomically large number.
And this doesn't even to take into consideration all the minute events that had to happen in each and every one of your parent's lives for them to even have met the person who'd they eventually have children with.
I think the sun would cease to be a main sequence star given those odds too.
So then, how does Craig explain these odds? The chances of each and every one of us having been born is unfathomably small, perhaps just as small as the evolution of homo sapiens if not smaller. I should have never been born, and no one should be writing this blog right now, and you should have never been born either and shouldn't be reading this blog right now. And just think of all the events that had to have happened in your life in just the way they did that would result in you reading this blog right now. So is it all a miracle as Craig claims? No. It's just chance. Someone was going to be born, or should I say something was going to be born (because there's no guarantee humans would have evolved) and what ever was born would be in our place. There's no rule that says you and I must exist.
But for the theist seeking validation for their beliefs, any time anything happens that is improbable they'll always use that as justification for a miracle. But is it justified?
Are rare events actually miracles?
Craig, it seems, is also unaware of the definition of the word miracle. A miracle by definition is a violation of the natural laws by supernatural means. That means that no event, no matter how improbable, whether it's the evolution of homo sapiens, or the birth of you or me, is by definition a miracle if no laws of physics were violated in any such occurrence. The problem here is that all too often the word 'miracle' becomes improperly used in our everyday colloquial use of the term to refer to things outside of its true definition.
What Craig does very well, is use a play on words and numbers to try to confuse his audience to twist the evidence in his favor. The fact that human evolution is improbable is a total red herring because everything that happens and every living being that is born is improbable. And to the theist who is entertaining the idea that each and every one of us is a miracle chosen by god, as some theists believe, then consider this: in order for my parents to have been born, World War II had to have happened exactly the way it did. If it didn't occur or if it ended differently, my parents would not have been born, and neither would I. But if you think that god engineered all of this for my benefit, you'd have to believe that god made 60 million people violently die, many of them tortured and killed, just so that I could have been born. Any such idea would make god the cruelest monster who ever lived.
So in the end - no - evolution is not evidence for the existence of god, it's actually evidence against the existence of god. For god to have used evolution to create mankind would mean that he knowingly used a process that resulted in millions of years of suffering, during which consciousness would arise so that this suffering could be experienced by sentient beings, and all for no logically necessary reason. Conscious suffering that exists for no logically necessary reason is simply incompatible with the idea of an all-loving god who is infinitely good and incapable of cruelty. I've worked that into a logical argument in my evolutionary argument against god. I welcome all challenges to it.
Craig may be able to fool his minions and the flocks of sheep who follow in the faith, but he ain't foolin' the skeptics who are on to his intentionally misleading ways.
*Mathematical calculations provided by http://members.shaw.ca/tfrisen/chances_of_you_existing.htm