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*To*: <mike@tecc.co.uk>*Subject*: Re: Mass Extinction Statistics*From*: "philidor11" <philidor11@snet.net>*Date*: Fri, 25 May 2001 19:55:35 -0400*Cc*: <dinosaur@usc.edu>*References*: <Pine.OSF.4.21.0105242305340.15938-100000@marlowe.umd.edu> <006801c0e4d0$ea776e80$e4e9fc40@oemcomputer> <E153EzA-0000sm-00@fw-smtp.tecc.co.uk>*Reply-to*: philidor11@snet.net*Sender*: owner-dinosaur@usc.edu

<Suppose there are twenty million mammals in a given environment (ten million placentals, ten million marsupials). The K/T bolide strikes, and 90% of them, chosen randomly, are killed. Then we know statistically that the remaining distribution will still be very close to fifty-fifty: that is, five million each would survive, give or take a few hundred thousand or so.> (Just a little math, 10% of 20 million equals 2 million total survivors. End of math; concepts have to be explained in clear, non-technical language, whether in stats or paleontology itself.) Ah, Mike, you're making a bunch of assumptions. Let's make some alternate assumptions: #1, all the placentals live in the East and all the marsupials live in the West. A bolide strikes and, assumption #2, the effects are so intense in the East that not a living thing survives. In the West, the effects are less intense, assumption #3, and 20% of mammals survive; which individuals are in the 20% and which in the 80% killed is decided randomly. They're all marsupials. 10% of all mammals have survived, and they're all marsupials. You made the assumption: chosen randomly, which could apply only if the effects attempting to kill the animals were equivalent everywhere. As I mentioned earlier, it seems pretty unlikely that the impact affected every square inch of the Earth in exactly the same way. And you're making another assumption, that secondary effects are equivalent. I used only primary effects in the example I gave: animals are alive, the bolide hits, animals are dead. However, I think that the assertion that secondary effects are important is reasonable. As an example of secondary effects, the death of a certain type of plankton can cause the extinction of a whole group of land animals years later. When you have a chain of causality, the opportunity for randomness, even random events after the impact, to influence the outcome is huge. (I think HP Pigdon also made this point in a post I encountered while this was in draft.) The original issue here was whether it is possible to assume that there is an identifiable cause for disproportionate survival. I'm saying that even if we exclude aspects of the animals involved and everything about fossilization and other problems with the record of those animals, the bolide is so likely to have differential effects that survival could be disproportionate; that you still couldn't draw unarguable conclusions from what lived. One more: if the bolide effects were the same everywhere in both primary and secondary effects, you still could have random events occur well after the impact which become highly significant for a reduced population. For example, more placentals survive than marsupials, but then the excess are killed by a forest fire. I'm a practical statistician; I calculate gambling odds and sometimes devise prize structures at work. This issue doesn't seem to me to require much more than a simple recognition of the existence of significant randomness after the bolide impact, the results of which cannot be isolated from other factors in a single trial.

**References**:**Re: Mass Extinction Statistics***From:*John Bois <jbois@umd5.umd.edu>

**Re: Mass Extinction Statistics***From:*"philidor11" <philidor11@snet.net>

**Re: Mass Extinction Statistics***From:*Mike Taylor <mike@tecc.co.uk>

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