No, you read the article you quoted: Under "Foods", the section you linked:

... Ultimately, animals must obtain vitamin B12 directly or indirectly from bacteria, and these bacteria may inhabit a section of the gut which is distal to the section where B12 is absorbed.

Under "synthesis and industrial production":

.... Neither plants nor animals are independently capable of constructing vitamin B12.[30] Only bacteria and archaea[31] have the enzymes required for its synthesis.

And a little later:

.... The total world production of vitamin B12, by four companies (the French Sanofi-Aventis and three Chinese companies) is said to have been 35 tonnes in 2008.[40] Most of this production is used as an additive to animal feed.[41][citation needed]

It doesn't matter what the top source on the list is if you can have it synthesized in your own body. Which I now do way better than I could before my first fast. You know why cow liver has B12? Because cows are fed B12 these days so that beef liver would have enough B12 for human consumption! That's so ridiculous and inefficient it is sad.

You know why B12 synthesis is so horrible among both humans and livestock today? Because of how much we use antibiotics. And there's also another surprising finding: The human body (and most other mammals as well) have a cache of the organisms required to synthesize B12 and a host of other useful stuff. It's called "The appendix", you might have heard about it. The body will release these organisms from its cache under ketosis lasting more than a few days, to replenish and revive the useful colonies. Nature is very smart like that -- a few days of fasting are completely normal when your food source dries up. So the body uses that period to do maintenance. [I'm not going to spend time looking for the refs right now, partly because I no longer have access to full article texts, and mostly because I don't have the time; But this was hypothesized decades ago, and AFAIK conclusively proved something like 5 years ago, although it's not really well known so far even among professionals who should know better]

> Stupid. Dangerous.

Religious, is all I can say about your responses. You know things to be right, like it is dangerous to fast, or (I assume, although you might already be enlightened about these subjects) that dietary cholesterol is bad for you (it's almost independent of blood cholesterol, which is an important marker, though not a cause for disease), that you shouldn't eat more than a few eggs a week (nonsense; eat as many as you want - 20 a day is not unhealthy), that low-fat dietary intake is good for you (it's not), that butter is bad for you (it's excellent for you if it's from healthy grass-fed cows), that weight change is exclusively a result of caloric balance (only in the useless tautological sense), that you should minimize salt intake (too little is as bad as or worse than too much), or that cushioning is good for your feet and that's why sports shoes have them (they're bad for you except for very specific circumstances; they were championed by marketers, not researchers).

I try to challenge my beliefs and understand why I have them. I often (way too often, unfortunately) find that things everyone (including myself) takes for granted are actually better classified as "wrong leaps of faith" or even downright superstitions than science.

When someone contradicts me (and it's something I haven't researched and do not have a good basis for my beliefs), I try to start again from a blank slate, rather than find support for what I believe in (because you always can do that, regardless of how wrong you are).

> Edit: Thinking about it, I'd put fasting for 3 weeks in the same class as running a marathon: if you can do it, you're probably healthy. Actually doing it though, is not healthy at all.

I don't think this analogy is proper.

Evolution surely did prepare you to run short distances. Evolution did not prepare you to run a marathon - you have to practice to be able to do that, regardless of how healthy you are - and I agree it is probably not healthy (although I have no support for that - for all I know, done properly, it might be super healthy).

Evolution did prepare you to survive if your food source dries up (at least for a short while), or if you sprained your ankle and can't chase your prey or climb the tree to get food. In fact, it's apparently piggybacked some maintenance jobs on this period because (at least pre- agriculture) they were guaranteed to happen relatively often.

You may argue about how long that "short period" is - evidence collected mostly from religious fasting is that it is around 40 days when you are healthy.

> if you can do it, you're probably healthy.

I disagree in general, but there's an important point here that I must stress - it would probably have been unhealthy for me, had my appendix been removed (which is not uncommon), given the explanation above. However, the reason I started fasting was not religious or weight motivated - I simply had no appetite. So I didn't eat. The appetite came back 21 days later. I have since fasted several times in periods of 7-21 days, once every couple of years, sometimes prompted by loss of appetite, and sometimes by wanting to experience the health benefits.

I would not be surprised if appendix removal would have triggered appetite much earlier. And I would also not be surprised if evolution did not prepare humans for a removed appendix, and I would have suffered some irreversible damage as a result. I really don't know about that. (If you feel vindicated about this being "stupid and dangerous" - we have a difference of philosophy here, that I'm not going to argue about)

* edit: Forgot to mention - I've been vegetarian for the most recent 90% of my life, and vegan for a nontrivial part of that - during which I never had a good source of B12. If B12 could only be sourced from food intake, I'd be dead before the age of 12 (which is why I already knew 15 years ago that the prevailing B12 theories were bullshit, despite not having a better explanation at the time). But I was only dangerously low for a 6-month period in my twenties - other than that, I was just "low, but not dangerously so" until that fast.