He doesn't have any evidence like that. He is merely pointing out that if we were to ask that question, among experts, we would get post-facto explanations which he would take with a heap of salt (because of the anthropic bias).
Taleb's brand of rationality, which he calls empirical skepticism (as opposted to just empiricism or just skepticism), largely trupmpets uncertainty. I think he sees this as against Bayesians (because Bayesians will usually choose an artificially narrow hypothesis space when making formal Bayesian models, and as a result, will usually get answers which are much more certain that is merited). He hasn't yet spoken about Bayesians specifically, though-- just "nerds" (statisticians who lack street smarts). When reading his stuff, though, I feel it converts well into Bayes. He is just saying that we shouldn't allow our beliefs to converge faster than is merited.
People are overconfident far more often than underconfidant.
So, his point with the black plague is really that we should answer "I don't know" if we are asked such a question, and even if an expert gives a better-sounding answer, we should assume it's an example of the narrative fallacy.
The point of his argument, if I understand correctly, is that we should expect a bubonic plague in the future to be more of an x-risk than it was in the past, because our past evidence is filtered by anthropic considerations. And because his argument isn't in any way specific to the plague, he will expect x-risks in general to be more prevalent in the future.
However, I don't understand how to quantify this. How much should I update towards the next bubonic plague being an x-risk? A little? A lot?
The historical plague could have wiped out humanity, but for...
I have just finished reading the section on anthropic bias in Nassim Taleb's book, The Black Swan. In general, the book is interesting to compare to the sort of things I read on Less Wrong; its message is largely very similar, except less Bayesian (and therefore less formal-- at times slightly anti-formal, arguing against misleading math).
Two points concerning anthropic weirdness.
First:
If we win the lottery, should we really conclude that we live in a holodeck (or some such)? From real-life anthropic weirdness:
It seems to me that the right way of approaching the question is: before buying the lottery ticket, what belief-forming strategy would we prefer ourselves to have? (Ignore the issue of why we buy the ticket, of course.) Or, slightly different: what advice would you give to other people (for example, if you're writing a book on rationality that might be widely read)?
"Common sense" says that it would be quite silly to start believing some strange theory, just because I win the lottery. However, Bayes says that if we assign greater than 10-8 prior probability to "strange" explanations of getting a winning lottery ticket, then we should prefer them. In fact, we may want to buy a lottery ticket to test those theories! (This would be a very sensible test, which would strongly tend to give the right result.)
However, as a society, we would not want lottery-winners to go crazy. Therefore, we would not want to give the advice "if you win, you should massively update your probabilities".
(This is similar to the idea that we might be persuaded to defect in Prisoner's Dilemma if we are maximizing our personal utility, but if we are giving advice about rationality to other people, we should advise them that cooperating is the optimal strategy. In a somewhat unjustified leap, I suppose we should take the advice we would give to others in such matters. But I suppose that position is already widely accepted here.)
On the other hand, if we were in a position to give advice to people who might really be living in a simulation, it would suddenly be good advice!
Second:
Taleb discusses an interesting example of anthropic bias:
You'll have to read the chapter if you want to know exactly what "argument" is being discussed, but the general point is (hopefully) clear from this passage. If an event was a necessary prerequisite for our existence, then we should not take our survival of that event as evidence for a high probability of survival of such events. If we remember surviving a car crash, we should not take that to increase our estimates for surviving a car crash. (Instead, we should look at other car crashes.)
This conclusion is somewhat troubling (as Taleb admits). It means that the past is fundamentally different from the future! The past will be a relatively "safe" place, where every event has led to our survival. The future is alien and unforgiving. As is said in the story The Hero With A Thousand Chances:
Now, Taleb is saying that we are that hero. Scary, right?
On the other hand, it seems reasonable to be skeptical of a view which presents difficulties generalizing from the past to the future. So. Any opinions?