Probability is an established branch of mathematics with very logical principles. In is a basic underpinning of quantum mechanics. The fact that the public considers probability some sort of black box with no real validity is one of the major shortcomings of our educational system. While probability can be used logically it is not usually involved when I say someone's logic is faulty. When you are dealing with many unknowns it is necessary to take probability into account or action becomes frozen until more data is available. While this may seem desirable, inaction often carries its own set of risks as is the case with BD's stance.

When I say that someone has made an error in logic it is usually because they are self contradicting or basing conclusions on a logic chain with a big gaping whole in it. BD does both quite often. In addition he seems to have no concept of how to judge probability or that it has relevance in decision making. These are separate critiques of BD. I will try to take your advice into account and do a better job separating these two approaches in the future.

In the case in question, John Rummel used an example in his reply to Zubrin which did not support the point he was trying to make yet it is often quoted by others because he is "The Planetary Protection Officer". Zubrin's point was not that we only need to worry about human diseases. It was that Martian pathogens are unlikely to affect Earthly organisms due to a lack of coevolution. He used the Dutch Elm disease vs humans as an example of an organism that did not coevolve with another host being unable to attack it. Rummel's counter erred on two points. 1) It treated Zubrin's comment as a human centered one when it was not. 2) Dutch elm trees don't grow on Mars either.

Now I agree with Rummel and Keith that there are other considerations and that small percentage of pathogens attack in a way that gets around this general rule. Keith has admitted however that these types of diseases do not have the types of lethality that Barry uses as examples to scare people about
MSR. To accuse Zubrin of oversimplyfying is correct, to accuse him of making a totally irrelevant point is quite another. Rummel seemed so intent on putting Zubrin in his place that it was not clear in his reply which he was trying to do in my opinion. He played right into BD's hands as is obvious by the numerous times BD has posted the link to Rummels article.

I thought both Race's and Rummel's replies were based more on personal interaction with Zubrin than what he actually wrote. The third article actually addressed more specifically the points Zubrin had made in his article. I find this intro to have been the most accurate evaluation of Zubrin's position:

"I (and most biologists) would (and do) agree with some of his statements. For example, the likelihood of life on Mars is small, and the likelihood of more advanced, mammalian-like life is even smaller. Moreover, the likelihood that a Mars organism pathogenic to Earth life exists and that, if it did, it could compete with highly adapted and competitive life on Earth is very small. None of this is new-it is comprehensively reviewed and discussed (with proper citations) in a National Research Council report ("Mars Sample Return: Issues and Recommendations," Washington, DC: National Academy Press, 1997). This report, produced by actual experts, visits virtually all of the issues brought up by Zubrin and is, in fact, in general agreement with many of his statements. The problem is that Zubrin selectively ignores other facts and takes things out of context. For example, the following cannot be ignored:"

The fact that none of this is new and that it is available in a readily available report should be sufficient basis for anyone to wade into the public debate. The decision on MSR is ultimately political and the debate should be understandable to at least the scientifically literate public.

He also noted in counter point to Keith's credential siting: "This is an interesting statement from someone who, according to my brief research, has no credentials in biology, microbiology, evolution, epidemiology, or pathology. Not that such credentials are prerequisite to speaking up for the right thing, but in the absence of supporting citations, one wonders what expertise bolsters such a strong stand."

See http://planetary.org/html/news/opinions/safescience.html for further details.

I have many minor quibbles with Kenneth H. Nealson including the fact that citations are not generally included in oped pieces and that there are quite a lot of biology experts that Zubrin has associated over the years, but I think his overall criticism of Zubrin as well as qualified support on some issues is accurate and more to the point than Race's and Rummel's comments.

Zubrin's response to all three is at
http://planetary.org/html/news/opinions/zubrinresponse.html and points out issues which none of them addressed. This whole issue is not the sole responsibility of one field. It involves aerospace engineering issues, biology issues, and interplanetary transport issues. Any claim that you have to be a biologist to wade in on this topic is bogus. Should the biologists shut up because they don't have the training to assess the impact of added precautions on mission reliability or the probability of suitable transport meteorites being ejected from a planets surface? I think not. It is a topic which experts from various fields need to openly discuss the issues involved.

Regards,
Mark