I think that it's fairly obvious that there wouldn't be even the relatively small percentage of seriously Christian scientists there are today if it had not been for centuries of proselytization, conversion by the sword, teaching Christianity to children from when they could talk, crusades, etc. I think it's also fairly obvious that this is not true of the percentage of scientists who are atheists. I also think it's obvious that it's not true for the percentage of scientists who think that, for instance, there are an infinite number of twin primes.

Typically one only notices these "memetic effects" in ideas one already disagrees with.

Really? I haven't heard anyone say "nobody would think there are infinitely many twin primes if they hadn't been taught that as a 4 year old and forced to verbally affirm the infinity of twin primes every Sunday for the next few decades". It just is not something that is said, or can sensibly be said, for any idea that one disagrees with.

Personally I would discount "believed by a large number of clever people" if there are memetic effects. There are traits of beliefs that are well-known to increase the number of believers for reasons unrelated to their truth. For any belief that has such traits, whether it's shooting unbelievers, teaching them to your children before they reach the age when they are likely to think rationally, or sending out missionaries, the large number of people who believe it is not much use in assessing its truth.

I would also discount anything which fits into certain patterns known to take advantage of flaws in human thought processes, particularly conspiracy theories.

In my experience, Guess culture (which I think is more fair to describe as "Hint culture") works really well when most people around me were raised in the same culture. We all know each other's expectations because we grew up together, and we all know how to communicate messages to one another implicitly, in ways that allow for a request to be turned down without the need for explicit rejection and all the emotional consequences of that, and we make use of that shared context in our daily interactions to reduce social friction.

Of course, it makes life difficult for outsiders who interact with us, and haven't grown up with that context, and therefore don't know how to communicate messages implicitly in our culture, and don't know how to interpret the implicit messages we send them. Outsiders are either mute or boorish (or perhaps both).

Conversely, Guess/Hint culture works really poorly in culturally heterogenous environments, when basically everyone is an outsider.

I observe that culturally heterogenous environments are a lot more common in the world than they were, say, 200 years ago; advances in transportation and communication tech probably account for that.

So that's one factor that seems relevant. (Of course, one could apply your argument again to claim that cultural heterogeneity is a new development and therefore suspect, and it's probably optimal for us to live in small isolated tribes.)

Guess culture has, I think, been the standard way for humans to hume for many thousands of years. My inclination is to imagine that, therefore, it's probably optimal, at least for typical people.

Am I missing something? Is there some factor that is pushing rules of social etiquette in a bad direction throughout human history?

The second word in the winning secret phrase is pony (chosen because you can't spell the former without the latter); I'll accept the prize money via PayPal to main att zackmdavis daht net.

(As I recall, I chose to Defect after looking at the output of one call to Python's random.random() and seeing a high number, probably point-eight-something. But I shouldn't get credit for following my proposed procedure (which turned out to be wrong anyway) because I don't remember deciding beforehand that I was definitely using a "result > 0.8 means Defect" convention (when "result < 0.2 means Defect" is just as natural). I think I would have chosen Cooperate if the random number had come up less than 0.8, but I haven't actually observed the nearby possible world where it did, so it's at least possible that I was rationalizing.)

(Also, I'm sorry for being bad at reading; I don't actually think there are seven hundred trillion people in Europe.)

Yvain explicitly said "Wikipedia's Europe page".

Regarding motivation for exercise, I find competition & praise is particularly helpful, perhaps especially for those of us of the male persuasion.

Fitocracy is kind of fun and has various challenges. Last summer I did various cycling & running challenges and eventually ended up so motivated that I completed a 100 km ride and a marathon, essentially for fun.

Alternately you could make bets with a friend about some well-defined goal like being able to do 100 pushups at a sitting.

Is cis or trans identity really something that is truth-apt (& therefore in the purview of probability)?

Could you explain what you mean by this via an easier to grasp concept than gender identity, preferably in a way that preserves relevance to identity?

A literature professor might ask: What happens when you see Hamlet in terms of Dennett"s epistemology as opposed to the epistemology of Aristotele?

If you want to ask that question it doesn't matter whether the epistemologies are true.

And if you want to ask the question of whether a yeti could defeat a Mongolian death worm it doesn't matter whether they exist. What is the purpose of seeing Hamlet in terms of this or that epistemology?

if we stop thinking about the fact that as an abstract, general question a random human being is much more likely to be cis than trans

That said, it could also be taken as advising you not to double-count your priors by using them to discount the evidence. Imagine you've drawn a ball from an urn, and the ball looks blue to you — but your priors say that 99% of the balls in that urn are red. How much time do you want to spend questioning the validity of your color vision or the lighting before you consider that you drew a rare ball?