Dracil’s BlogJournal

April 21, 2008

Evolution, probability, and you

People like to say, “Oh evolution is impossible blah blah random chance.”  Aside from the fact that such statements belie a lack of basic understanding about evolution, we can play a fun little game about what “impossible odds” really means.

Step 1) First, think about your own birth.  Basic sex ed. will teach you that you were made from your father’s sperm and your mother’s egg. The average male produces 12 trillion sperm in their lifetime.  The average female about 2 million eggs at birth.  What are the odds that the one sperm and the one egg from your father and mother happened to meet?  1 out of 12 trillion multiplied by 1 out of 2 million.

Step 2) Think about how many of your direct ancestors died in their childhood. ;)  Ok, that was just for fun, but it’s an interesting exercise nonetheless that reveals a bit about yourself.  Now, think about the odds that your direct ancestors, and their direct ancestors, all the way to the beginning of whatever you believe to be the beginning of the human species were born, by applying Step 1 for each of them.  For each ancestor you have (remember, every generation higher roughly doubles the number of ancestors, assuming no incest), multiply the probability of that ancestor’s existence to the probability of your existence.  Are we done?  Great!  Let’s move on to the next step.

Step 3) Now let’s look at the world population.  6.6 billion.  What are the odds for each person that exists today to exist, given what you figured out from Step 1 and 2?  Now, what’s the probability for everyone that exists today to exist simultaneously given that?  It’s the number from step 2 to the power of 6.6 billion.

I think you’ll realize that the probability of your existence, and everyone else’s existence is so small as to be essentially meaningless.  One might as well say 1 in infinity.  Yet, here we all are.

While not meant to seriously address the claim from the beginning, I trust that after going through this exercise, you’ll understand that what people say is “impossible” is not necessarily all that impossible, especially when one is in the present and looking at past events.  In fact, you could say the probability of everything that has already happened to be exactly 1 (out of 1).


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