Re: Extinction

[John Bois <jbois@umd5.umd.edu>]

On Tue, 3 Dec 1996, Stan Friesen wrote:

>... in the Lancian deoposits there were about 10-12
> species of dinosaurs and more than 20 species of mammals, perhaps as
> many as 30.  Thus 300 green marbles and 100 red is more like reality.
> Now add 50 pink marbles, and 150 blue marbles, and 100 yellow ones,
> and some more of several additional colors.
> 
> Now, select 75% of the marbles.  What is the probability that all of
> *at* *least* *one* color are chosen (not necessarily red)? [From a
> statistical point of view, this si the correct question, not the
> probability of choosing all red]. There is actually quite a high
> probability that at least one group will be completely wiped out. But
> the mammals, being the most diverse group, are the least likely to
> buy the farm.

Where am I going wrong?  Using your "data" I made 72 little slips of 
paper and colored 30 green (mammals), 12 red (dinos), 5 pinks, 15 blues, 
10 yellows.  Then I took out 30%--and your 75% extinction rate is  
high.  In Ward's Nov. _Science_ paper 70% is cited so I used that--or 22 
slips at random.  I simulated 10 K/T extinctions.  Only one species became 
extinct (Yellow) and that only happened once!!!  By chance alone, dinos 
did very well: of their 12 "species" the following numbers surived the 
ten successive K/Ts--8,8,5,7,5,3,7,5,4,6. 

        I know it can't be that simple.  Like I said, where am I going
wrong?