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Comment author: ChristianKl 10 December 2014 11:46:09PM 1 point [-]

The phylogenetic tree model is used because it makes useful predictions about the world, not because it represents the way the world actually is.

Yes. I'm not denying that such models do have use. But on the other hand people outside of biology do often consider them to represent the world as it actually is.

Comment author: faul_sname 11 December 2014 01:24:32AM 0 points [-]

I think we're in agreement here.

Comment author: ChristianKl 09 December 2014 03:04:00PM 0 points [-]

but in practical terms it is useful to have a tree-like map, because it allows you to assess the phylogenetic distance between two groups.

That works as long as a virus doesn't transfer genes from one species to the next and thus invalidates the tree structure.

Comment author: faul_sname 10 December 2014 08:24:40PM 1 point [-]

It depends on your goal. What a lot of non-biologists don't realize is that the ladder keeps going after species down through subspecies and beyond. In terms of bacteria, which do undergo horizontal gene transfer, we generally refer to them by their strain in addition to their species. The strain tells you where you got the culture, and, in lab settings, what it's used for. CAMP Staphylococcus aureus is used for the CAMP test, for example -- because you know where the strain comes from, you can be reasonably confident that it will behave like other bacteria of that strain. If you have a different strain of Staphylococcus aureus, you expect that it would probably also work for this test, but by the time you get as far away as Staphylococcus epidermidis, it's quite unlikely that you could use it successfully for the CAMP test.

In theory, you could do a DNA extraction and see if your organism has the right genes to do what you want. In practice, it's usually cheaper and easier to use a strain that you know has the right characteristics -- even among bacteria with 20 minute generation times, genetic drift is still pretty slow, and what little selective pressure there is is pushing for the strain to keep its useful properties (i.e. we throw away bad cultures).

The phylogenetic tree model is used because it makes useful predictions about the world, not because it represents the way the world actually is.

Comment author: IlyaShpitser 08 December 2014 12:12:51PM *  3 points [-]

"Species" is not a clean concept in a world with viruses, clines, and ring species.

More precisely, "species" is a map marker made by someone who likes discrete, mostly tree-like maps (legacy of Aristotle?)

Comment author: faul_sname 08 December 2014 08:29:15PM 2 points [-]

"Species" is one rung on the phylogenetic ladder. Whether a given edge case should be classified as a species or as a subspecies can be debated, but in practical terms it is useful to have a tree-like map, because it allows you to assess the phylogenetic distance between two groups.

Also, compared to the range from class to genus, "species" is relatively clear-cut.

Comment author: Nornagest 08 December 2014 05:31:29PM 1 point [-]

How'd you manage to strikethrough part of your post? I thought the markup for that had been disabled.

Comment author: faul_sname 08 December 2014 06:56:22PM 2 points [-]
"hello, world".replace(/(.)/g, '\u0336$1') == "h̶e̶l̶l̶o̶,̶ ̶w̶o̶r̶l̶d̶"
Comment author: Nornagest 04 December 2014 07:25:15PM *  3 points [-]

Jehovah's Witnesses != Mormons, even though both are known for door-to-door solicitation. Reliable statistics are thin on the ground, but the Mormons seem to be doing a little better than average in terms of personal socioeconomic status. (BYU is not, however, an unbiased source.)

Comment author: faul_sname 04 December 2014 11:37:47PM 1 point [-]

You are correct. I'm not sure where I got the idea that LDS was Jehovah's Witnesses.

Comment author: Lumifer 04 December 2014 03:36:33PM 1 point [-]

For whom? For the Mormon Church or for the specific individuals? :-/

Comment author: faul_sname 04 December 2014 07:10:50PM *  -1 points [-]

I̶t̶ ̶a̶p̶p̶e̶a̶r̶s̶ ̶m̶o̶s̶t̶l̶y̶ ̶t̶h̶e̶ ̶c̶h̶u̶r̶c̶h̶,̶ ̶a̶p̶p̶a̶r̶e̶n̶t̶l̶y̶.̶ ̶W̶o̶w̶.̶

Edit -- missionary.lds.org is latter day saints. One of their quotes was by a Jehovah's Witness, so I thought this was a guide for Jehovah's Witnesses. If the question is "Does it work for the specific individuals in the Mormon Church?" the answer is yes.

Comment author: Lumifer 01 December 2014 08:36:25PM 9 points [-]

And you end up like this.

Comment author: faul_sname 04 December 2014 09:28:37AM 10 points [-]

Seems to have worked for them.

Comment author: Strange7 30 November 2014 12:11:57AM 4 points [-]

Alright, so you bring this alleged time traveler with you to visit two or three different psychologists, all of whom are appropriately surprised by the whole 'time travel' thing but agree that you seem to be perceiving and processing the facts of the situation accurately.

Furthermore you have a lot of expensive tests run on the health and functionality of your brain, and all of the results turn out within normal limits. Camera-phone videos of the initial arrival are posted to the internet and after millions of views nobody can credibly figure out how it could have been faked. To the extent that introspection provides any meaningful data, you feel fine. In short, by every available test, your sanity is either far beyond retrieval down an indistinguishably perfect fantasy hole, or completely unmarred apart from perhaps a circumstantially-normal level of existential anxiety.

Now what?

Comment author: faul_sname 30 November 2014 09:36:34PM 1 point [-]

Then I accept that there's a time traveler. The evidence in this second situation is quite a bit stronger than a personal observation, and would probably be enough to convince me.

Comment author: dxu 26 November 2014 02:08:14AM *  1 point [-]

Well, the insanity defense is always a possibility, but then again, you have no proof that you're not insane right now, either, so it seems to be a fully general counterargument that can apply at any time to any situation. Ignoring the possibility of insanity, would you see any point in refusing to update, i.e. claiming that what you just saw didn't happen?

Comment author: faul_sname 26 November 2014 04:43:34AM *  2 points [-]

It's always a possibility that I'm insane, but normally a fairly unlikely one.

The baseline hypothesis is (say) p = 0.999 that I'm sane, p = 0.0001 that I'm hallucinating. Let's further assume that if I'm hallucinating, there's a 2% chance that hallucination is about time travel. My prior is something like p = 0.000001 that time travel exists. If I assume those are the only two explanations of seeing a time traveler, (i.e. we're ignoring pranks and similar), my estimate of the probability that time travel exists would shift up to about 2% instead of 0.0001% -- a huge increase. The smart money (98%) is still on me hallucinating though.

If you screen out the insanity possibility, and any other possibility that gives better than 1 in a million chances of me seeing what appears to be a time traveler with what appears to be futuristic technology, yes, the time traveler hypothesis would dominate. However, the prior for that is quite low. There's a difference between "refusing to update" and "not updating far enough that one explanation is favored".

If I was abducted by aliens, my first inclination would likewise be to assume that I'm going insane -- this is despite the fact that nothing in the laws of physics precludes the existence of aliens. Are you saying that the average person who thinks they are abducted by aliens should trust their senses on that matter?

Comment author: dxu 23 November 2014 04:35:07PM *  1 point [-]

I don't think the quote is talking about "hypothesizing" anything; I read it more as "You have to update on evidence whether that evidence fits into your original model of the world or not". Instead of "hypothesizing time travel when things don't make sense", it'd be more like a stranger appears in front of you in a flash of light with futuristic-looking technology, proves that he is genetically human, and claims to be from the future. In that case it doesn't matter what your priors were for something like that happening; it already happened, and crying "Impossible!" is as illegal a move in Bayes as moving your king into check is in chess.

Not that such a thing is likely to happen, of course, but if it did happen, would you sit back and claim it didn't because it "doesn't make sense"?

Comment author: faul_sname 25 November 2014 08:47:59PM 2 points [-]

Yes. And then I would go see a psychologist. Because I find it more likely that I'm losing my grip on my own sanity than that I've just witnessed time travel.

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