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*To*: dinosaur@usc.edu*Subject*: Randomness and Probability (off topic)*From*: Dann Pigdon <dannj@alphalink.com.au>*Date*: Fri, 25 May 2001 17:33:39 +1000*References*: <Pine.OSF.4.21.0105220827010.13102-100000@marlowe.umd.edu>*Reply-to*: dannj@alphalink.com.au*Sender*: owner-dinosaur@usc.edu

John Bois wrote: > Given roughly equal diversity before, random action should yield > 50/50--or do I misunderstand how this statistical process works? It would seem to me that, if you could put a precise probability value to something, then it isn't random. Tossing a coin is a random action *each time you do it*, however there are only two possible outsomes (technically not true - the coin could land on its edge and stay there!), each mutually exclusive, and each throw does not affect the next one at all. Given only two possible outcomes, and equal likelihood, then over an infinite number of tosses the stats should approach 50/50. Randomness only comes into play in the short term. The results of an infinite number of tosses will not be random (provided there actually is equal likelihood for the two outcomes - the air resistance of the design on one side of the coin may subtly affect the toss so as to favour one side over the other in a large number of tosses). If you start talking about random variables playing havoc with something as complex as an ecosystem, however, then there are clearly more than just two outcomes, and anything affected by these random interplay of variables is not an independant event. It can (and usually will) feed back into the system, creating further chaos. Suggesting that the interplay of random variables (that is, more random than usual) into an ecosystem will result in equal measures of extinction in two separate groups is far too simplistic for my tastes. -- ____________________________________________________________ Dann Pigdon Australian Dinosaurs: GIS Archaeologist http://dannsdinosaurs.terrashare.com Melbourne, Australia http://www.alphalink.com.au/~dannj/ ____________________________________________________________

**References**:**Re: A long post about DUMB METATHERIANS vs EVIL, SMART PLACENTALS***From:*John Bois <jbois@umd5.umd.edu>

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