The Probability of Life

Voltaire
4 min readOct 14, 2023

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The question of the probability of any one individual’s existence is a deep and complex one. When considering the vast sequence of events leading up to any one person’s existence, the odds can seem almost infinitely small. Here’s a simplified breakdown:

Chance of Your Parents Meeting:
Let’s say the odds of your parents meeting at any point in their lives is 1 in 20,000.

Chance They Stay Together Long Enough to Have Kids:
Maybe 1 in 2,000.

Chance of the Right Egg Meeting the Right Sperm:
The average human male will produce about 525 billion sperm cells over a lifetime, and the average female ovary contains about 300,000 to 400,000 eggs at puberty (though only about 500 will ovulate). The odds of the exact sperm from your father fertilizing the exact egg from your mother is roughly 1 in 200,000 trillion.

Ancestral Lineage:
Consider the odds that every one of your ancestors managed to survive to reproductive age and reproduce, going all the way back to the first humans and beyond (to the dawn of life). Given the dangers of prehistoric life, natural calamities, wars, diseases, and so on, the odds here could be exceptionally low.

Random Genetic Shuffling:
Even if all the right ancestors met and reproduced, the unique genetic recombination that makes you distinct also had to occur.

Considering all these events and more, the odds of you existing are so small that they’re practically zero. Dr. Ali Binazir has given a colorful analogy, saying that:

“The odds of any one person existing are about the same as if two million people threw a trillion-sided die, and they all landed on the same number.”

Adding in the Drake Equation

The Drake Equation is used to estimate the number of active, communicative extraterrestrial civilizations in the galaxy. By combining this with the probability of intelligent life on earth we can get an estimate of how many other human-like species there can be in the universe.

Let’s walk through this step by step.

N=R∗×fp​×ne​×fl​×fi​×fc​×L

Where:

  • N is the number of civilizations in our galaxy with which communication might be possible.
  • R∗ is the average rate of star formation in our galaxy.
  • fp​ is the fraction of those stars that have planetary systems.
  • ne​ is the average number of planets that can potentially support life per star with planets.
  • fl​ is the fraction of those planets that develop life.
  • fi​ is the fraction of planets with life where intelligent life evolves.
  • fc​ is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
  • L is the length of time civilizations can communicate.

Drake Equation Real Data

For the equation, let’s use the actual numbers we have available from the data we have gathered:

  • R∗: 1 star forms per year in the galaxy.
  • fp​: 20% of those stars have planets (0.2).
  • ne​: 20% of those have Earth-like planets in the habitable zone (0.2).
  • fl​, fi​, fc​: For the sake of simplicity, let’s say each of these is 1% or 0.01.
  • L: The length of time civilizations can communicate. This is highly variable, so for simplicity, let’s ignore it for now.

Given these numbers:

N ≈1×0.2×0.2×0.01×0.01×0.01=4×10−7N≈1×0.2×0.2×0.01×0.01×0.01=4×10−7

This suggests there might be 0.0000004 civilizations in our galaxy with which we might establish communication, based on these conservative estimates. Of course, the actual galaxy has hundreds of billions of stars, so you could multiply this number by that to get a rough number of civilizations.

Probability of Humans Existing

From our previous discussion, the odds of any one human existing, considering all the events in human history and the genetic recombination that led to you, is astronomically small. Let’s say for simplicity it’s 1×10−101×10−10.

Multiplying the Two Together

If we multiply the two probabilities together we get:

4×10−7×1×10−10=4×10−174×10−7×1×10−10=4×10−17

This is a tiny number. It suggests that, given these conservative estimates, the probability of another human-like species on one of those planets is almost:

ZERO PERCENT

There are no Aliens.

I am sorry.

You have the best wetware that life can evolve.

It took billions of years of death and chaos to get here.

The probability of you existing is 1 in trillions.

You hit the lottery. Act like it.

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References:

https://www.seti.org/drake-equation

https://exoplanets.nasa.gov/search-for-life/drake-equation/

https://www.nasa.gov/mission_pages/kepler/overview/index.html

https://blogs.harvard.edu/abinazir/2011/06/15/what-are-chances-you-would-be-born/

https://pubs.aip.org/physicstoday/article-abstract/14/4/40/422237/Project-Ozma?redirectedFrom=fulltext

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