This was originally posted on a horrible site called Myspace. When Myspace underwent a redesign in Fall 2010, hundreds of insightful reader comments that had been left over the years were lost. I have since deleted my account there.
Several months ago I came across a quote from the geneticist and author Richard Dawkins that I found incredibly profound: "Not a single one of your ancestors died young. They all copulated at least once." (New Yorker magazine, 9/9/96)
Think about this for a second. Assuming that you believe life really did evolve over millions of years (and I think we're pretty sure it did), what does that mean? It means that thousands, tens of thousands, hundreds of thousands, millions even -- indeed, many tens of millions of generations IN A ROW absolutely, positively must have survived at least to reproductive age in order for you to be here today reading this blog.
Have you ever watched a nature program? It's a dog-eat-dog world out there. Sea-turtle eggs hatch in the sand, and the young crawl toward the water, only to be snatched up in large numbers by waiting gulls. And it wasn't that different for our distant ancestors. By any stretch of the imagination, it's an unfathomable, freakish "accident" for any given person to exist. Think of the odds: Joe DiMaggio's hitting streak of 56 consecutive games may never be broken -- and decent players have something like a 70% chance of getting at least one hit in each game. How does one of the greatest feats in sports stack up to the odds of tens of millions of consecutive surviving generations preceding you, me, and billions of other people on the planet?
A religious person (who doesn't reject evolution) might say this proves that a loving God had a plan to bring you into this world. It's a good argument, as theistic arguments go, although of course it ignores the 99.99999+% of lineages that didn't make it. Instead, this incredible "accident" only shows how silly it is to argue that Earth must have been set up by God to be a fertile place for life, that the favorable conditions are too much of a coincidence. Whatever the odds are that a planet would have water, moderate temperatures, a protective magnetic field, oxygen (eventually), etc. -- I'm sorry, but all of that is much, much more likely to occur than for tens of millions of consecutive generations of animal ancestors to dodge eons' worth of predators, diseases, and hazards (no healthcare, ever, mind you) and survive to maturity. And yet, we're all here, aren't we?
Another argument a theist might make: How did all of those species survive, through millions of years of evolution and countless extinctions (including several massive ones), such that the human lineage as a whole is around today? And an atheist would counter by pointing out that if they didn't, we wouldn't be around to notice that we didn't make it (see: the anthropic principle).