Here, I found this pretty picture: a tiny fraction of the hundreds of millions spermatozoa (sperm cells) swimming as fast as they can, to be the first to enter the egg cell.  Guess who won?

This is how you started: you won the race against incredible odds.  Odds is an odd word, but then so is odd; why does it need two ‘d’s: od would look odd, but sounds the same.  It is derived from a peak of land, then became a triangle, then for not-paired, being the third point. Odd being left on its own, somehow became probability, for the odds is just another way of saying what’s the probability.  The minor difference is that odds is stated as 1 in some number; and odds against when that number is less than 1; and probability is generally stated as a decimal or percentage.  In history, all probabilities have become 0 or 1; until we know whether the event happened or not, its chance of happening, or probability will be a number between 0 and 1, like 0.5 which is exactly in the middle.  Here the odds are even; like whether you get heads or tails when you toss a coin.  But let’s get back to your story.

If another sperm had won, it would not have been you.  Strange thought, but well done for winning that race with bigger odds against you than winning the lottery:  one sperm in 100 to 500 million just for that race; but you might not even been able to enter that race, if your mother had become pregnant with the egg she released the previous month.  So, what is the probability that YOU are here, instead of the brother or sister that could have been here instead?  And if your parents had not met; and so on.

You need to be careful not to mis-use probabilities.  They have no bearing on history; it already happened; it’s either 0 or 1; and even though the prior probability was so close to 0 that the one that you call you should be here; the probability is actually 1, because you are here.

Want to do some arithmetic? If not, skip the square brackets.

[Let’s round out to saying there are 16 sperm in the picture, and there were  128 million (128,000,000) sperms competing for that egg.  Now if you happen to know that 16 = 2^4 and 128 = 2^7, then you know that 128 divided by 16 is the same as subtracting the exponents of the common base.  The ^ symbol means ‘to the power of, or ‘exponent’.  It’s the number of times the number is multiplied by itself. So, 128/16 =2^7 -2^4 = 2^(7-4) = 2^3 = 8.  And there  was a 1 in 8 million chance that ‘your’ sperm won. What’s that probability? But now that you’re here, its odds are 1 in 1 – it already happened.]

[[{Ever heard of log tables?  Before we had calculators, they were used to simplify complex calculations by converting a number (x) to its ‘exponent’ (y) or logarithm: [x = 10^y].  Adding the logs is the same as multiplying the numbers; subtraction division.  The result is found in the anti-log table where the resulting exponent(y) is converted back to a number (x). }]]

In epidemiology, the science of disease distribution and determinants, careful use of data is vital.  The Texas sharp-shooter fallacy: shoots first in the wall, then draws the target around the bullet hole.  To state that you have beaten the odds to be here is kind of like that.  Can you see the analogy?

Once something has happened, what does it mean to calculate the odds of it happening.  The lady who just won the lottery did not beat the odds, she just won.  Even though winning was incredibly unlikely, and very much against the odds to the tune of one in close to a billion; those odds no longer carry any information once she won; and somebody had to win!

Knowledge is very slippery, so is logic.  Words are the problem.  They aren’t real; and they can never fully describe reality.  We can just get close. Shall we try?