Thursday, May 26, 2005

Evolution and Probability

Here is a good New Yorker article explaining and debunking the few theories supporting "intelligent design" that have attempted to disguise themselves with a scientific face. This is via Red State Rabble which has good coverage of all the goings-on in Kansas.

One of the primary arguments that the creationism/"intelligent design" movement offers against evolution is its improbability. The chances that life would have emerged from a chemical soup and then evolved into the complex structures we see today is miniscule, they argue. Something I have not seen argued is that by doing so they commit the elementary fallacy of confusing conditional probability with direct probability. That is, we shouldn't be looking at the probability that humans evolved, but the probability that humans evolved GIVEN that humans exist today. We should include all available information in our probability calculation.

I tried to do the calculation using Bayes' Rule but there's a lot of estimation for which I have little basis. There are a lot of numbers bandied about for P(humans evolved) but few (or none!) for P(humans exist | humans evolved) or P(humans exist | humans did not evolve) which you would need. But given that P(humans exist | humans did not evolve) is very very very small (which I think is reasonable since how many other options are there? Alien transplantation? God?) then P(humans evolved | humans exist) is not tiny at all.

(Keep in mind also that all these probability calculations should be done from the perspective of Earth 6,000,000,000 years ago. So P(humans exist) should really be P(humans exist 6,000,000,000 years from now), etc.


Anonymous DICK said...

I have not heard this perspective before...find it quite interesting.
Anyone can take any supposition, no matter how far-fetched...claim it correct...and dare anyone to refute it. Seems it is politically correct to allow credence to any rediculous assertion rather than call a spade a spade. This is how religions are born and progress. Needy people can follow any path. P.T. Barnum was too conservative; there are more than one sucker born every day.

8:29 AM  

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