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Re: Mass Extinction Statistics



<What's the difference whether I increase the population or the number of
bolide strikes?  Flipping a flippin' coin a hundred times is the same as
flipping 100 [different] flippin' coins once.>
You're right.  And the event you're looking at is 100 coin flips, 100 events
or trials.
Here we're flipping the coin once for the bolide event.  If we assume that
each animal, whether marsupial or placental, is equally vulnerable to the
effects of the bolide, that there is no significant physical difference
protecting either type of animal, that does not guarantee that the effects
of the bolide will strike equally in each group.
Take a more familiar example.  Any animal can be fossilized.  Does the
discovery of 3 animals of a species who obviously died in different times
and places mean that the animal was more likely to be fossilized than an
animal represented by only a single fossilized individual?  Obviously not,
if both animals were of similar size and other physical factors influencing
the likelihood of fossilization.
Does the 3 to 1 ratio even mean that the animal fossilized more often
probably lived in an area with soil, etc more likely to produce fossils?
Maybe, but not certainly.  Maybe those 3 individuals wandered into the
'right' area at the 'right' time, while the animals who actually lived in
the area just happened to die in the 'wrong' place consistently.
By the way, this problem with fossils also means the fossil record is not a
good indicator of the actual ratio of survivors of the bolide.
So, equal vulnerability/susceptibility does not mean an equal number of
survivors.  Other factors, like being in the 'wrong' place at the 'right'
time could influence the result, even if you had a record of every
individual placental and marsupial alive at the time.
If you had enough bolide strikes, the random (lucky/unlucky)
survivals/deaths would balance each other out for each group, and you would
be able to combine all the different results to confirm that in fact each
group was equally vulnerable/susceptible.  Or not.
I know that it can appear a single strike gives sufficient opportunities for
luck to balance out, but say for instance the bolide happened by chance to
affect some areas more than others, though all areas are devastated.  And
say that the most affected areas happened to have higher concentrations of
placentals than marsupials.  That would make placentals apparently more
vulnerable.  A second strike might afflict marsupials disproportionately and
the numbers would even out.  You can't assume the affects are evenly
distributed across animal population densities.
Having enough repetitions allows you to separate the random from the
underlying factors.  Too few repetitions keeps you from knowing whether
you're looking at a fluke.
Thanks for the chance to think about this.  To be clear, it's necessary to
identify and lay out all the factors.