What needs explanation is how a harmful random mutation can spread to a significant proportion of the population.
Easy.
The harm is easily avoided. For example, an allergy-against-bananas gene might not affect one’s reproductive fitness at all in the modern world—one merely needs to avoid bananas.
The “harm” is to the society, not to the individual. For example, a mutation (in males) that causes all children born to be male will not harm the person carrying the gene, but will end up with fewer total greeding pairs in subsequent generations.
A guy with the harmful mutation just happens to have a lot of wealth of political power—and takes a few dozen wives.
(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.
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.)
Also remember that nothing is perfectly neutral. Even the banana man might get fed banana-cake by a dastardly enemy.
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....)
Easy.
The harm is easily avoided. For example, an allergy-against-bananas gene might not affect one’s reproductive fitness at all in the modern world—one merely needs to avoid bananas.
The “harm” is to the society, not to the individual. For example, a mutation (in males) that causes all children born to be male will not harm the person carrying the gene, but will end up with fewer total greeding pairs in subsequent generations.
A guy with the harmful mutation just happens to have a lot of wealth of political power—and takes a few dozen wives.
(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....)