If a mutation doesn’t decrease the reproductive capacity of the carrier, then it’s not harmful. If it’s harmful, then it will affect the reproductive capacity. That’s just how it’s defined in this context.
Sorry, it took me a little while to go through the Boyko paper. It’s super statistics heavy. What I’m reading from there is that 27.3–29.0% of mutations are neutral, 30-42% are moderately deleterious, all the rest are highly deleterious or lethal. The statistics indicate that 10-20% of mutations have been fixed by positive selection (again assuming a common ancestor with chimpanzees). Deleterious, as you mentioned, specifically means harmful to reproduction. So in this context, diseases like Huntinginton’s, hemophilia, familial ALS, sickle cell, Lynch syndrome would be considered “neutral”. These statistics are mostly derived from Americans of African decent, as the clustered rate of mutation in Americans of European decent was too high to model well.
The Jonsson paper had a similar average rate of mutation of order 10^-8 per base pair as the other paper we looked at, which translates to about 3 per generation.
So what I don’t understand, and maybe you can help me, is that in the extreme case of 20% of mutations being avoided by positive selection, there’s still 7% of mutations with potentially horrific consequences. This is already excluding the over 70% of mutations that decrease reproductive fitness. What evolutionary pressure is there to keep “neutral” genetic diseases from accumulating in a population over time? How can “beneficial” mutations outweigh this burden? Mathematically, it seems to me that macro evolution is impossible. Am I missing something?
No worries, I can also be slow to respond. There’s a few things at play here:
Neutral mutations can become beneficial later on. It’s not just about the genes, it’s also about the environment. Even deleterious mutations can become beneficial, like sickle cell disease likely being selected for due to its protection against malaria.
Following from that, deleterious/neutral/beneficial are pretty loose categories, and it’s not even really correct to think of them as categories. It’s more about how beneficial it is. Sickle cell disease is bad, but better than dying of malaria.
Beneficial mutations can be really beneficial. Once somebody has them, they can spread like wildfire through the population. One example is the ability to digest lactose as an adult. It’s “worth” lots of “failures” to get that mutation (using those terms loosely and without value judgement). An analogy might help here, think about it kind of like this slime mold searching for food. The tips have a lot of churn and waste, but the food it finds is worth doing all that work. You can think of the beneficial mutations as the branches that are kept.
(Note that evolution isn’t directed by “something”, even as simple as a slime mold, it’s a description of a physical process, like gravity, so the analogy is loose)
We’ve seen beneficial mutations happen in person, and shows another example of how useful beneficial mutations can be: https://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment. The E. coli evolved the ability to digest a new substance they couldn’t before. The experiment also touches on neutral mutations sticking around.
The distinction you’re drawing between micro evolution and macro evolution relies on an assumption that either there are different kinds that are inherently distinct, or some sort of “system” that prevents micro evolution from progressing into macro evolution. For the prior, I’ve never seen a defense of that that doesn’t rely on the supernatural, and for the latter, what happens when the system itself changes due to evolution?
In my personal experience, the strongest argument against any radical move away from the current general scientific worldview consensus is that everything generally fits together. Sure, the estimated age of the universe might be adjusted slightly from 13.7B to 13.8B years, or the Jurassic might actually be estimated slightly wrong. But across all evidence we have, the current scientific understanding across a diverse range of disciplines is approximately correct. Nobody is counting tree rings and saying “Wait a minute, these show the Earth is 6,000 years old!”. Nobody is dating rocks and saying “Hold on, this dates as twice as old as the universe!”. Note that you’ll find claims of things like fossilized tracks of humans walking next to dinosaurs, but those don’t pan out
Sorry, it took me a little while to go through the Boyko paper. It’s super statistics heavy. What I’m reading from there is that 27.3–29.0% of mutations are neutral, 30-42% are moderately deleterious, all the rest are highly deleterious or lethal. The statistics indicate that 10-20% of mutations have been fixed by positive selection (again assuming a common ancestor with chimpanzees). Deleterious, as you mentioned, specifically means harmful to reproduction. So in this context, diseases like Huntinginton’s, hemophilia, familial ALS, sickle cell, Lynch syndrome would be considered “neutral”. These statistics are mostly derived from Americans of African decent, as the clustered rate of mutation in Americans of European decent was too high to model well.
The Jonsson paper had a similar average rate of mutation of order 10^-8 per base pair as the other paper we looked at, which translates to about 3 per generation.
So what I don’t understand, and maybe you can help me, is that in the extreme case of 20% of mutations being avoided by positive selection, there’s still 7% of mutations with potentially horrific consequences. This is already excluding the over 70% of mutations that decrease reproductive fitness. What evolutionary pressure is there to keep “neutral” genetic diseases from accumulating in a population over time? How can “beneficial” mutations outweigh this burden? Mathematically, it seems to me that macro evolution is impossible. Am I missing something?
No worries, I can also be slow to respond. There’s a few things at play here:
Neutral mutations can become beneficial later on. It’s not just about the genes, it’s also about the environment. Even deleterious mutations can become beneficial, like sickle cell disease likely being selected for due to its protection against malaria.
Following from that, deleterious/neutral/beneficial are pretty loose categories, and it’s not even really correct to think of them as categories. It’s more about how beneficial it is. Sickle cell disease is bad, but better than dying of malaria.
Beneficial mutations can be really beneficial. Once somebody has them, they can spread like wildfire through the population. One example is the ability to digest lactose as an adult. It’s “worth” lots of “failures” to get that mutation (using those terms loosely and without value judgement). An analogy might help here, think about it kind of like this slime mold searching for food. The tips have a lot of churn and waste, but the food it finds is worth doing all that work. You can think of the beneficial mutations as the branches that are kept.
(Note that evolution isn’t directed by “something”, even as simple as a slime mold, it’s a description of a physical process, like gravity, so the analogy is loose)
We’ve seen beneficial mutations happen in person, and shows another example of how useful beneficial mutations can be: https://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment. The E. coli evolved the ability to digest a new substance they couldn’t before. The experiment also touches on neutral mutations sticking around.
The distinction you’re drawing between micro evolution and macro evolution relies on an assumption that either there are different kinds that are inherently distinct, or some sort of “system” that prevents micro evolution from progressing into macro evolution. For the prior, I’ve never seen a defense of that that doesn’t rely on the supernatural, and for the latter, what happens when the system itself changes due to evolution?
In my personal experience, the strongest argument against any radical move away from the current general scientific worldview consensus is that everything generally fits together. Sure, the estimated age of the universe might be adjusted slightly from 13.7B to 13.8B years, or the Jurassic might actually be estimated slightly wrong. But across all evidence we have, the current scientific understanding across a diverse range of disciplines is approximately correct. Nobody is counting tree rings and saying “Wait a minute, these show the Earth is 6,000 years old!”. Nobody is dating rocks and saying “Hold on, this dates as twice as old as the universe!”. Note that you’ll find claims of things like fossilized tracks of humans walking next to dinosaurs, but those don’t pan out