For many of us, the story behind our parents meeting is ridiculously improbable. It's true for me: My father met my mother in a bar in Montreal in the mid-'70s. She was a student from Sydney, Australia, and he was from New York City. He and his friend made a bet over a backgammon board: Whoever won the game would ask her out. I was one result of two out-of-towners at the same bar, a spark of mutual attraction and a winning round of one of the oldest board games in the world. It's pretty ridiculous, but not the most outlandish of these types of stories.
But even if your parents' meeting wasn't unlikely, your existence still is. Looking purely at the numbers, the chance of any of us existing is ridiculously tiny. Here are just a few of the reasons why:
1. The chances that your parents met, then had sex, and that the particular sperm and particular egg that made you (and not another version of your parents' genetics) is 1 in 400 quadrillion — which looks like this: 400,000,000,000,000,000.
And that's just the beginning of the crazy probability game that led to your existence, outlined in the video below:
2. The chance for any of your ancestors to have met and have sex and that their egg and sperm produced your particular set of parents, grandparents and great-grandparents is also beyond minuscule (multiply that 400 quadrillion a few quadrillion times). In my case, my grandparents and great-grandparents almost all came from different countries around the world (a common enough story in the U.S. and Australia, immigrant nations both), so their meeting at all was less likely than someone whose grandparents grew up in the same town. But it almost doesn't matter; those probabilities are all so small they are close to zero anyway. And if your family history shows people coupling over lines of race, religion or ethnic differences, well, add another few zeros to your unlikely existence, since the vast majority of humans have kids with people within their own ethnic group.
3. That your ancestors didn't die in a bloody conflict, from disease or by accident before they had a chance to reproduce is remarkable. That's a separate set of factors outside people meeting and mating, but historical events are intertwined with people getting together, too. Then consider about 150,000 generations of humans have continued in a long line all the way to you. And before your human ancestors got together, their animal precursors did too (each with their own set of unlikelihood) — all the way back to the single-celled organism from which all life began.
Which brings us to how amazing it is that life on Earth exists at all: Conditions here are ideal for a variety of life, but only because of an incredibly complex set of (low-probability) events. Just a few include:
4. The other planets in our solar system protect us. Planets much larger than Earth protect our blue marble from possibly destructive asteroids and comets that are constantly streaming through our space neighborhood. Without that strong gravitational pull sucking up flying debris, that destructive debris would land on Earth — causing massive weather disruptions like the one that likely killed the dinosaurs 66 million years ago.
5. The moon makes life on Earth possible. Earth's moon creates tides in our oceans and the dynamic environment that results is good for evolving life — intertidal organisms were an important step between sea creatures and later land animals. The moon also stabilizes Earth's orbit and keeps its rotation more regular than it might be on its own. Without the moon, the Earth's axial tilt would be more extreme (like Mars), and we would have times when half the planet was dark for six months, while the other side would get toasted by the sun. Plenty of planets don't have moons; that we do is thanks to a random celestial event 4.5 billion years ago that could have turned out differently. Life on Earth as we know it wouldn't exist without the moon, as this video explains:
6. The Earth is the right temperature for life — not too hot and not too cold. According to BioLogos: "All evidence suggests that the Earth was inhospitable to life for the first 700 million years, largely because it was so hot. However, the Earth gradually cooled, and 4 billion years ago it became more hospitable. Within little more than 100 million years, the first single-cell life forms appeared." Compared to other planets, our hot/cold variability is quite small; stable conditions give room for complex life forms to evolved over time.
While some of the above probability calculations seem impossible, there's a major problem with doing calculations at all: As John Horgan writes in Scientific American, "Unfortunately, you cannot determine the probability of the universe or of life on Earth when you have only one universe and one history of life to contemplate. Statistics require more than one data point. The utter lack of empirical data does not stop scientists and philosophers from holding strong opinions on these matters. We are either pawns of destiny or wildly improbable flukes. Take your pick.”
I'll go with wildly improbable flukes, because whenever I look at my life that way, all those day-to-day stresses and frustrations just don't seem important anymore. That I'm here to write this and you're here to read it is — statistically — almost impossible.
P.S. I would love if you would share your parents' how-we-met story in the comments!