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johnlawrenceaspden comments on A Medical Mystery: Thyroid Hormones, Chronic Fatigue and Fibromyalgia - Less Wrong
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Absolutely, a famous example is Queen Victoria's mutation that caused haemophilia in some of her male descendants. The queen really does seem to have been the mutant, and it was just a rotten bit of luck!
What needs explanation is how a harmful random mutation can spread to a significant proportion of the population. One way that can happen is if it's actually also a defence against something, and another is if the heterozygote version is good, but the homozygote is harmful.
With a large fitness advantage, mutations can spread quickly! Consider a lightning plague like the black death. It wiped out a third of the population of Europe in a couple of years, and then simmered and flared for centuries. A 'harmful' gene that defended against that would have had a whale of a time, and you'd expect to see it in all Europeans.
But if it's really harmful, you'd expect that over the last 600 years, better defenses might have evolved, and the previous defence might start evolving back out.
About 500 years ago, all the old world plagues were introduced to the Americas at once, and they literally decimated the native population. I don't know if there are any 'pureblood' native americans left, but if there are, their genes should be a mass of defensive scars.
Easy.
(1) Sure, but that sort of thing will just random-walk, it would take ages to go from one mutation to 50% of the population. It has almost no fitness effect. It will probably get gambler's-ruined out.
(2) Absolutely, and we see those things in animals. You can evolve to extinction. In the particular case of a male-causing gene, I think it would have to stabilize very low (because the more successful it is the more harmful it is to the carrier) , but you can certainly imagine (and find) driving genes that just become rapidly prevalent and wipe out the species.
(3) Yes, but that's just the random walk walking. It has to get very lucky to become prevalent, and if it's actively harmful, it won't get that lucky, and that will kill it off eventually.
A mutation needs an edge to spread fast.
In general, harmful mutations will die out. In order to spread to a significant proportion of the population, yes, a random mutation has to be lucky. It has to random-walk in a very rare way, and it is still more likely than not going to hit the gambler's ruin and be eventually eliminated from the population, even if it first spreads to 99% of said population (an extremely unlikely event).
But the thing about random-walking is that it is random. One wouldn't bet on a given harmful mutation spreading fast (not if one wanted to win the bet)... but if there are a million harmful mutations, then one of them could reasonably be expected to have one-in-a-million luck.
I think we're pretty much on the same page. But have you actually calculated the odds? One in a million is no big deal. Twenty half-chances.
I must say I haven't, and I don't know how to (especially since it's all screwed up by genes moving around and getting passed on together, and I don't understand the first thing about all that). But it feels more like 'thermodynamic entropy' than 'winning the lottery'.
Also remember that nothing is perfectly neutral. Even the banana man might get fed banana-cake by a dastardly enemy.
No, I haven't actually calculated the odds. I wouldn't really have much of an idea how. (I could probably work it out on a basis of - if a gene has x% chance of preventing descendants as compared to not having that gene and a y% chance of being passed on to any descendants - and then do some overly-simplified calculations from the values of x and y - but I haven't, yet.)
True, but his problem there isn't the banana gene. His problem there is that he has a dastardly enemy. If he didn't have the banana gene, the dastardly enemy could simply feed him arsenic cake instead, or just shoot him.
The official name of a mutation winning despite having no selection benefit is genetic drift. When I had genetics lessons in university the concept that was taught was that a significant amount of our genetic changes are due to gene drift but there's no exact way to quantify how many.
Furthermore some genes aren't stable and can easily mutate. Evolution doesn't succeed in bringing color blindness to zero despite it being no useful mutation.
Yes, an obvious one is the inability to manufacture Vitamin C. Universal in great apes, including us, but every other animal and plant can do it, except guinea pigs.
I imagine that at some point our ancestors lived in a vitamin C rich environment, so losing this was no immediate handicap. But even then, the random drift should have taken ages. Is there some reason why losing this pathway would be a benefit?
Same for colour-blindness. Is it drifting, or is it actually good for something in an environment where it does no harm? (These poor children, none of them will ever be commercial pilots or qualified electricians....)
"Literally decimated" would have reduced the population by 10%. Some Native American groups were hit much harder than that. (I think the "mound builders" in what is now the southeastern US may have actually disappeared completely.)
Accepted. I have managed to use decimated in the wrong way. Sorry.
Minus the "literally", though, the word "decimated" in current English uses would include much more severe population declines. I'm just being unnecessarily pedantic.
Spectacular pedantry is sort of where I'm coming from here, though. And actually literally can be used metaphorically too, and has been for some centuries. I'm confidently expecting this to be the most controversial assertion in this entire discussion, so you can go look for your own references. [Openly trolling now]
In fact, how did any of them live through that? Did the vikings take some diseases and some genes over with them early doors?
Did the Vikings ever get out of Newfoundland? Is there any evidence they made it to the mainland?
According to Wikipedia, yes, the Norse made it to continental North America in pre-Columbian times and made multiple voyages there to obtain natural resources (primarily fur and timber), but did not establish any permanent colonies (perhaps due to hostile relations with the native Americans (which the Norse called the Skrælings)).
I asked about the mainland. The Vikings made it to Newfoundland, certainly, but Newfoundland is an island.
The Wikipedia article mentions that a Norwegian coin from King Olaf Kyrre's reign (1067–1093) was allegedly found in a Native American archaeological site in the state of Maine, but does not mention any definitive evidence that the Norse made it to the mainland.
Yes, I know. That's why I asked :-/
I have no clue. Is there a vikingologist in the house?
Tuberculosis keeps coming up. It was deadly and recent and widespread, and it's implicated in the 'plausible mechanism' paper, and in the one about rheumatoid arthritis, and the other day I met an old friend with bladder cancer. Apparently he's having tuberculosis drugs injected to try to kill it. No one knows why, but it works about 30% of the time!
It would be way interesting if someone had statistics for ancient diseases and statistics for modern unexplained diseases. I've no idea what to predict, but I bet it's not 'no correlation'.
Have you seen Greg Cochran's paper on infections?
Yes, I based the entire second post on it, and referenced it. But thanks, that would have been really useful!
I just emailed the address on the paper (paul ewald) to see what they thought of it. But no reply. If anyone knows one of them could you tell them there's someone wrong on the internet?