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Re: Extinction (of marbles)



From: Wabandco@aol.com

 > Stan Friesen writes, "You shouldn't be asking about red specifically,
 > you should be asking what the probability that *some* color (any
 > color) is missing from the final pick of survivors.".  I would posit
 > that you would need to consider the number of species of all organisms
 > extant at the time, and the number of those that were dinosaurs, and
 > ask the probability that *all* of the dinosaur species would be
 > missing, and *most* of the mammals would survive, and so on.  ...

You are still explicitly singling out the dinosaurs and mammals in your
"test".   When you do this you are no longer testing for randomness.
You are instead testing for the probability that dinosaurs *specifically*
became extinct.

Also, in all of my posts I have always *excluded* those groups with
low extinction rates, on the grounds that such low rates occur in more
groups than expected by chance. That is, there is a nonrandom factor
that distinguishes between "immune" groups (those whose extinction rates
are no higher than normal background), and "susceptible" groups (with
a higher than background extinction rate).

Now, last night I went over Archibald's data again, and I noticed
something that I had forgotten - the placental mammals are in the
*immune* group (0% extinction).  This means that there probabily *is*
a systematic factor that distinguishes them from dinosaurs.  However,
that same systematic factor also distinguishes them from marsupials
(with 91% extinction).

It should be clear that the difference between 91% (marsupials), and
100% (dinosaurs) is a trivial difference. It could easily have gone
the other way around, with marsupials all dead and a handful of
dinosaurs surviving.

I will post more detailed data from Archibald in another letter.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.