The probability of being me

Most kids ask their parents at some point: How did I get here? Some parents cringe because they don?t like discussing the physiological details of mammalian copulation. I suggest here another story that only briefly dwells on our Victorian hangups.

Thirty-seven years ago I was growing in my mother?s womb. I was a rapidly assembling network of neurons, muscles, glands and vessels. My growth was not pre-determined. My mother?s diet and environment exposed me to a dose of fish oil here (a good thing), a dash of environmental mercury there (a bad thing, thanks to the local coal fired power plant).

Since emerging into the sunlight, my semi-conscious life experiences have produced a person who is interested in exhibiting traditionally masculine traits most of the time, collecting bugs, and studying where I came from. To calculate the probability of me is to consider all these stochastic (random) influences since I was conceived.

But my essence extends prior to conception. My parents each produced a number of gametes (sperm and eggs) according to statistical rules, and two of these combined to form my zygote. Much of the information to make a human resides on 23 pairs of microscopic chromosomes, each pair of which split up to make gametes.

Independent assortment is the phenomenon that each member of the 23 pairs of chromosome had an equal probability of ending up in my ancestral gamete, so that 223 genotypes of gamete could be made. For those not near a calculator, this number is more than 8 million.

On a good day, my dad produced about 500 million sperm cells in each ejaculation, even though only one provided the information to make me. Each of these 500 million was probably unique, thanks not only to the 8 million independent assortments of chromosomes but also due to ?crossing over? of chromosomes, which provides even more possibilities.

?Crossing over? is the process by which the pairs of chromosomes, right before separating, trade sections of their chromosome with their partner chromosome.

The creation of the zygote whose cells I have inherited was not the only reproductive event in the history of the universe that directly led to me. For about 200,000 years before me, Homo sapiens was producing a generation every 20 years, so that I have about 10,000 Homo sapiens ancestors.

Farther back than that, my ancestors would be considered a different species but in the same genus for about 100,000 generations. Going back further, I would have about 10 million primate ancestors.

Since the first animals arose about 700 million years ago, I estimate I have about 1 billion animal ancestors. From there back to the first cell may add about 300 billion ancestors.

I am a winner, and so were all my ancestors. How many of my ancestors died young before reproducing or otherwise failed to reproduce? None. I am the result of trillions of virtual dice rolls.

Before this starts to sound like the greatest locker-room pep talk ever, it?s helpful to remember that everyone else you know is a winner too, even cousin Ralph, who wears a fanny pack more often than he wears a shirt.

I reflect on the long period of time required for humans to appear, and the millions of species that have come and gone prior to my own species, and the billions of ancestors in my lineage. I am a being made of chemicals, but yet can reflect in awe at the contingency of my own existence.

I posit that God did not predict me, but that God still delights in me. I hope that I am allowed this theological extrapolation, as I recognize that such should be done cautiously by scientists.

Mathematician Warren Weaver (1894?1978) wrote, ?We keep, in science, getting a more and more sophisticated view of our essential ignorance.? Modern scientific exploration is an exercise in humility. May we maintain the curiosity of children, and strive to be students of nature and history.

Having completed his tenure at Tabor College, Andrew Sensenig has accepted a teaching position at Fresno (Calif.) Pacific University.

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