The Improbability of Me (and You) by David R. Bowne

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microscopic close-up of cells

I try to live a life without regret. Not that I haven’t made mistakes, because I have, large and small. I just take the view that all events, the good, the bad, the vibrant, and the bland, have interacted to create my life. And not just life in the sense of my personal journey through the years, I’m talking life with a capital L. Because let’s face it, I shouldn’t be here. Not here as in this place, but here as in existence. I, the genetic entity tapping away at a keyboard, should not exist. And neither should you. But here we are. Talk about lucky.

This isn’t about humility. I have no problem with ego; just count my self-referential pronouns if you want proof. This is about math, plain and simple, and biology, not at all plain and not at all simple. Let’s look at the numbers. A human being has 46 chromosomes in the nucleus of every body cell. But our sex cells, our gametes, sperm in my case since I am a young, virile man (okay that’s a lie, except for the part about being a sperm-producing male), have 23 chromosomes. Not just any old 23 chromosomes mind you, but a very specific subset of the 46 because the 46 are not wholly different chromosomes. They are organized into 23 pairs of matching chromosomes, one of each pair supplied by mom and the other from dad. Each pair contains genes coding for the same trait. So if one chromosome has a gene for hair color, then its partner also has a gene for hair color, but it might be for a different color. Except of course, since I’m a dude, my sex chromosomes are an X and a Y and the Y is a small, pathetic little thing with fewer genes than the X. But let’s ignore the differences in sex chromosomes; the math of life is complicated enough as it is. And some species, like turtles, ignore sex chromosomes altogether. They just don’t have them. But we can ignore that too, since I can guarantee that I am not a turtle. I can type for one thing. A turtle would just flail at a keyboard – I tested this with my pet turtle. Nothing she typed made sense.

So in my gonads (yours too), the process of meiosis takes the 46 chromosomes, splits the pairs, and finishes with 23 single chromosomes in each sex cell. The order in which the pairs line up and separate is completely random. This isn’t like middle school gym class where the best are chosen first to make two teams. Each chromosome pair is split up but there is no pattern to which of the other recently single chromosomes end up in a gamete. So one gamete may have gotten all 23 of my dad’s chromosomes and none of my mom’s and another gamete may have received two paternal and 21 maternal. Here is where we get back to the math. With 23 pairs, there are 2²³ possible ways the chromosomes could be arranged. This makes for approximately 8.4 million unique combinations based only on the random line-up at the dividing line during meiosis. That’s 8.4 million unique genetic products from the identical starting point. Let’s say that again. Each cell at the start of meiosis starts with the same genetic make-up, but each of 8.4 million gametes is unique. From 1 to 8.4 million – that’s fucking crazy math and we haven’t even gotten to the fucking yet.

Because, as copulation leads to fertilization, one of each sperm with its 8.4 million unique combinations may hit the egg of some lucky lady (I told you I had no problem with ego) whose egg is also one of 8.4 million genetically unique ones. So the chance that the sperm having the unique genetic set that “would be me” (WBM) would hit the WBM egg is 8.4 million times 8.4 million, which is in the ballpark of 72 trillion. So the probability that I exist is at least 1 in 72 trillion. And however mind-blowingly unlikely it is that the random processes of independent assortment and fertilization created the unique genetic person that is me, the actual probability is much lower.

That’s because so far I’ve ignored the additional genetic variation that happens during the crossing-over process. This is going to sound crazy, but some genetic information is exchanged between the chromosome pairs during meiosis. A bit of the chromosome I got from my dad goes into the one from mom and vice versa. This results in each chromosome being a novel mixture of the maternal and paternal. With crossing-over added in the mix, each sex cell is much more than 8.4 million uniquely unique. The unpredictable nature of crossing-over makes the actual level of genetic uniqueness in each gamete practically impossible to determine. Suffice it to say it is much higher than the 8.4 million due to only independent assortment. So now the probability of me is a number much higher than 8.4 million multiplied by a number much higher than 8.4 million, which equals a number just shy of infinity. My chance of existence is just under one in near infinity. I am (and you are too) one of the most unlikely occurrences in the universe.

It’s almost enough to make me believe in a higher power–an omniscient being guiding the whole affair to make me, the very special genetic me. Just think of it. God guided meiosis in my dad to make that special sperm that is half the genetic code for me. His unerring supernatural fingers manipulated the position of chromosomes so that precisely the right ones end in the sperm and egg “destined to be me” (DTBM). And then in the ultimate arranged marriage, He had my parents discover each other from among the billions, forced them to wait to have intercourse until the precise moment that the DTBM egg ovulated while the DTBM sperm was produced and readied for launch. Then He made them have sex in a position (missionary of course!) so that my dad’s ejaculate would be best prepared to circumnavigate the sperm-killing wasteland that is the human female’s reproductive tract. The DTBM sperm valiantly swam alongside the hundreds of millions of brethren in the ultimate race to the ultimate prize. The DTBM sperm slogged through the mucus filled, acidic swamp of the vaginal tract, evaded the immune response of my mother’s body triggered by the onslaught of millions of flagellated invaders into her body, and sped past all the other sperm as God cleared a righteous path. Perhaps He parted the Red Mucus, allowing the DTBM sperm unhindered passage to the Promised Egg. God blew on the sperm and uttered sacred words of encouragement until finally it met its destiny, the monolith that is the DTBM egg. I was conceived. The angels rejoiced. God smiled, but then hoped He wouldn’t regret it. Because He already knew I wasn’t going to buy any of it.

So with all of the improbable events occurring throughout time resulting in the genetic entity that is me, I am not going to waste my accident of existence pondering what could have been. Instead, I rejoice in what I have, and am thankful for the results of incalculable randomness coupled with choices, good and bad. I am thankful that I somehow met a wonderful woman who could not only tolerate, but would actually want to marry, me, and that our own biological processes of independent assortment, crossing over, and fertilization should result in two remarkable children, both so amazingly improbable, both so perfectly unique, both so distinctly different, yet originating from the same place. How could I possibly regret any decision when every decision created them? I can’t. So instead of dwelling on what might have been, I celebrate the improbability of each of us as we use our highly improbable lives to achieve highly improbable things, however seemingly small they may seem.

David_BowneA scientist by training and a writer by inclination, David R. Bowne is an associate professor of biology at Elizabethtown College in Elizabethtown, Pennsylvania. When not mucking around in wetlands with students studying turtles and salamanders, teaching courses merging ecological science and creative writing, cheering on his two teenage children at swim and dance competitions, or enjoying quality time with his wife, he can be found tapping away in the dark of his basement office.

STORY IMAGE CREDIT: Flickr Creative Commons/George Sheperd

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