Dogmafood writes:
I find it truly astounding how successful organisms are at randomly producing a particular mutation that lends them immunity to a particular randomly appearing pathogen. The odds seem to be so incredibly high.
Here's a description of a simple experiment that illustrates what happens. A scientist places a billion bacteria in a petri dish with a growth medium containing a nutrient the bacteria cannot metabolize. Bacteria that could metabolize this nutrient would have a great competitive advantage over bacteria that did not. The bacterial genome has a billion nucleotide pairs.
As it happens, a single mutation in one gene would allow the bacteria to metabolize the nutrient, but the odds of this mutation occurring are a billion to one.
But there are a billion bacteria. If each bacterium divides once, what are the odds that one of them will experience the precise necessary mutation. By making some simplifying assumptions it becomes a simple calculation that only takes a half minute on a calculator, so I went ahead and did this, and the odds are 63% that at least one of the billion bacteria will experience that exact mutation. In reality the odds will be affected by factors I ignored, like how many of the other three nucleotides cause the desired effect, but the odds would still be pretty good. We'll be pessimistic and say the real odds are 10% that the needed mutation would occur in a single generation.
So what are the odds that the mutation would arise within 10 generations, which with a 20 minute generation time would only take around 3 hours? We'll assume that the bacterial population size remains at a billion. The odds are 65%.
And what are the odds that the mutation would arise within 100 generations, which would only take a little over a day? The odds are 99.99%.
How about that? If you're willing to wait a single day, it's a virtual certainty that that 1-in-a-billion mutation will occur.
--Percy