In Unweaving the Rainbow: Science, Delusion and the Appetite for Wonder, Dawkins writes:
We are going to die, and that makes us the lucky ones. Most people are never going to die because they are never going to be born. The potential people who could have been here in my place but who will in fact never see the light of day outnumber the sand grains of Arabia. Certainly those unborn ghosts include greater poets than Keats, scientists greater than Newton. We know this because the set of possible people allowed by our DNA so massively exceeds the set of actual people. In the teeth of these stupefying odds it is you and I, in our ordinariness, that are here.
Right around the time that DNA was being discovered, the wise Alan Watts intuited the same idea in his spectacular meditation on the ego and the universe, where he wrote: “Without birth and death, and without the perpetual transmutation of all the forms of life, the world would be static, rhythm-less, undancing, mummified.” But, biologically speaking, the existential roulette that landed on you out of the infinite not-you alternatives is set into motion well before your actual birth. Dawkins writes:
The lottery starts before we are conceived. Your parents had to meet, and the conception of each was as improbable as your own. And so on back, through your four grandparents and eight great grandparents, back to where it doesn’t bear thinking about.The instant at which a particular spermatozoon penetrated a particular egg was, in your private hindsight, a moment of dizzying singularity. It was then that the odds against your becoming a person dropped from astronomical to single figures.
In fact, that lottery extends beyond your lineage and stretches back in time into the origin of the universe itself:
How it feels to me, and I guess to you as well, is that the present moves from the past to the future, like a tiny spotlight, inching its way along a gigantic ruler of time. Everything behind the spotlight is in darkness, the darkness of the dead past. Everything ahead of the spotlight is in the darkness of the unknown future. The odds of your century being the one in the spotlight are the same as the odds that a penny, tossed down at random, will land on a particular ant crawling somewhere along the road from New York to San Francisco. In other words, it is overwhelmingly probable that you are dead.In spite of these odds, you will notice that you are, as a matter of fact, alive. People whom the spotlight has already passed over, and people whom the spotlight has not reached, are in no position to read a book… What I see as I write is that I am lucky to be alive and so are you.