I suspect that the informal nature of a talk might mean that one can describe things at an intermediate level of detail ("and so do this and that") that would look strange in a more formal paper, and so writers feel that they're stuck with either going into a full level of detail (which would be too much work to do for everything) or else saying "I'll leave this as an exercise to the reader"... even though going into some detail would be more useful to the reader.

they might have been healthy and tall

Gosh, I'd sure like to see some actual statistics on that.

According to Kevin Kelly in The World Without Technology, the reason why everyone in a HG tribe is healthy is because their life expectancy is so low that all their older and less healthy people are already dead.

Your explanation / definition of intelligence as an optimization process. (Efficient Cross-Domain Optimization)

That was a major "aha" moment for me.

I find the justified paragraphs hard to read, please change to left aligned / ragged right as most every web site does.

(There's a reason left aligned is standard on the web and justified paragraphs are standard in books and magazines: computer screens have a far lower resolution than printed material).

The register page should explain what is a valid username.

If I enter an invalid username, it should tell me what is invalid about it (instead of only displaying "Invalid user name", making me guess).

For a checklist for usability issues, I recommend a book: Defensive Design for the Web: How to Improve Error Messages, Help, Forms, and Other Crisis Points by 37Signals. (Each recommendation made in the book is pretty obvious; the purpose of having a checklist is to remember to do all of them :).

George, Brian: thank you for the elaborations. Perhaps the point is that if I have a mental model of when the mathematician will say what, and that model is reasonably accurate, I can use that information to make more accurate deductions?

Which seems fairly obvious... but perhaps that's also the point, that Bayesian statistics allows you to use what information you have.

"There's no reason to believe, a priori, that the mathematician will only mention a girl if there is no possible alternative."

Erp, I don't understand what this sentence is referring to. Can someone do me a favor and explain what is the "no possible alternative" here?

I have a newbie question... if A) quantum mechanics shows that we can't distinguish personal identity by the history of how someone's atoms got into the configuration that they are in, and B) morality (other things being equal) flows backwards from the end result, and C) it is immoral to allow a child to die on the railroad tracks, then D) why would it not also be immoral to decide not to marry and have children? Both decisions have the same consequence (a live child who otherwise would not be).

At some point we (or the machines we build) will be able to manipulate matter at the quantum level, so I think these kind of questions will be important if we want to be able to make moral decisions when we have that capability.

If I myself were given the task to program the little child life saving machine, I admit that right now I wouldn't know how to do better than a naive leads-to-child-living rule which would result in the mass of the observable universe being converted into habitat for children...

Assuming that we want it-all-adds-up-to-normalcy, we would hope to find a rule consistent with quantum mechanics that would end up with saving the life of a child on the railroad tracks having a higher moral imperative than converting the available mass of the universe into children (and habitat etc. so that they have happy fulfilling lives etc...)

The it-all-adds-up-to-normalcy approach though reminds me a bit of the correspondence principle in quantum mechanics. (The correspondence principle says that for large systems quantum mechanics should give the same result as classical mechanics). The principle was very useful when quantum mechanics was first being developed, but it completely broke down once we had large systems such as superconductors which could not be described classically. Similarly, I can imagine that perhaps my moral judgments would change if I was able to integrate the reality of quantum mechanics into my moral thinking.