You should also account for how myelinated the neurons are, and how many of them are not myelinated at all, since this affects neuron size and energy expenditure a lot.
Without myelin, the conduction speed of a neuron is mainly determined by its diameter. Some animals don’t have myelin at all, and their neurons can be huge because of this reason. I’m not sure if this applies to rodents, but it would explain why their neurons grow in size as the brain grows, because conduction distances grow too, and therefore you need a higher conduction speed, and this can only be achieved by having a larger neuron. Even humans have some neurons that are not myelinated, and they vary from this to highly myelinated with anything in between and their conduction speeds vary in proportion.
Connection count should also be an important factor, and it can vary by many orders of magnitude. It also matters how many neurons are active at a time.
There’s another thing to consider, which is that myelination requires special glial cells around axons to actually provide the myelin sheath, and these cells are relatively large themselves and use up energy. Glia (both for myelin and many many other functions) actually take up a large fraction of the space of the human brain and there are (by some estimates) 10x more glia than neurons in the human brain. The human brain especially has a lot of glia (90% of brain tissue) whereas for a mouse it’s only 65% of brain tissue.
IIRC myelinated neurons are both more energy efficient taking into account the glial cells and take less space than nonmyelinated neurons if we talk about similar conduction velocities. I’ll have to check this one just to be sure.
The human brain especially has a lot of glia (90% of brain tissue) whereas for a mouse it’s only 65% of brain tissue.
You mean the volume or the number of cells? This is certainly interesting and supports my hypothesis of why rodent neurons grow in size as their brains grow. What do you think?
Why are some brains less myelinated than others? Was their evolution just less lucky?
Possibly, but I’d caution against simplistic evolutionary arguments; evolution is rarely so simple. For instance, chimpanzees have higher axon myelination during development and adulthood than human brains do.
This point is highly suspect and should be easy to test. There are people who live on raw foodstuffs and do just fine. If you don’t believe it, try it for a while.
A raw food diet that a modern consumer with access to supermarkets and kitchen equipment might try would not resemble a raw diet in pre-agricultural times. Most raw food diets strongly recommend juicing, blending, mixing, etc. which are essentially pre-digestion. Furthermore, they’re also generally billed as “weight loss diets,” allowing sedentary people to lose weight without exercising—the calorie total might be in the 1000-1500 range.
Cooking greatly increases how many things you can eat, what’s safe to eat, and how many calories you can fit into your stomach. Cooking might decrease nutrient absorption by 5-10%,but when you can eat 50-100% more, it’s a fine trade.
I think you guys are just privileging a cool hypothesis a neuroscientist is making about gastroenterology. It’s pretty weird and frustrating how many objections this single point is getting, given that just like I already said, it’s very testable.
Most raw food diets strongly recommend juicing, blending, mixing, etc. which are essentially pre-digestion.
So is chewing and it works just fine.
Furthermore, they’re also generally billed as “weight loss diets,” allowing sedentary people to lose weight without exercising—the calorie total might be in the 1000-1500 range.
Who’s doing the billing? Are these people fat to begin with? Where are you getting these numbers from and do they really have anything to do with the foodstuff being raw?
Cooking greatly increases how many things you can eat, what’s safe to eat, and how many calories you can fit into your stomach.
Most foods you can make safe by cooking do not comprise a great deal of what people eat. Some of them could be unsafe raw just because human GI tracts are used to cooked food by now. Also, most foods don’t significantly shrink when you cook them.
Cooking might decrease nutrient absorption by 5-10%,but when you can eat 50-100% more, it’s a fine trade.
I can’t say I’m familiar with them, although I’ve occasionally eaten very little cooked food. Bulk of the calories could come from fish, milk, eggs, nuts, fruit and vegetables. Fish and eggs carry a risk of food poisoning if you don’t know your source. So does red meat.
It’s possible that this wouldn’t be a significant problem if your GI-tract and immune system were used to these kinds of threats however. It’s also possible that bacteria causing food poisoning are more potent and more common than they used to be or than they are in nature.
Requesting a data point: did your heuristics point to me being a proponent of raw foodism and trying to sneak in my ideology? I hadn’t even read about it before I made my comment.
I don’t encounter many people in my life who care about particular diets much and count myself amongst them. In fact, I know none irl. Do you find this unusual?
I don’t know a lot of people who do much with their diet. Offhand, I know two ex-vegetarians who still eat very little meat, one person who did CR for a few years, and one person who gave himself an eating disorder (I hope he’s over it) by following a claimed-to-be- healthy diet which was much too low calorie for him. Oh, and a woman who seems to be doing well on the same diet. And two people who are following some complicated diet which involves different types of food on a cycle. They’ve lost weight, but I’m dubious about their ability to maintain it. Rather more people than I thought before I started listing.
I know two people who are serious about supplements. One of them limits carbs drastically.
“Nutrition is the mind-killer.” Definitely true, and funny.
I’ve done a little survey about the effects of trying to lose weight, if you’d like to see some mind-killing and some non-mind-killed people. I’m trying to figure out how to deal with (other people’s) compulsion to give advice. Forbid it, or let it roar?
I’m not sure why there not being any would tell us anything, because cooking is common knowledge everywhere by now, and there are other reasons to cook food than nutrition.
because conduction distances grow too, and therefore you need a higher conduction speed, and this can only be achieved by having a larger neuron
That only suggests that peripheral neurons should grow with body size, not neurons in the brain. I suppose that it’s simpler to let central and peripheral neurons be the same size, but that doesn’t seem to me like a good reason.
Do you have a source for the quantitative variation of myelination between vertebrates, and not just the binary question of some have it (vertebrates), some don’t?
Do you have a source for connection count varying between species?
Here’sevidence that axonal diameter grows as brains grow, and that axonal diameter is important for conduction speed.
If you read that article, you will realize that the degree of myelination in a species will depend on how fast conduction they need, since if conduction speed is not taken into account, nonmyelinated fibers are much cheaper to have.
I didn’t have a source at hand for variation of connection count, but found this.
“The neocortex undergoes a complex transformation from mouse to whale. Whereas synapse density remains the same, neuron density decreases as a function of gray matter volume to the power of around −1/3.”
This means that synapse count per neuron varies considerably between species.
This point is highly suspect and should be easy to test. There are people who live on raw foodstuffs and do just fine. If you don’t believe it, try it for a while.
Do they? (the Wikipedia section refers to raw vegan diets, but I suppose that eating significant quantities of raw meat, fish or dairy poses a risk of infection by bacteria or worms)
Your gut flora would probably be completely different and more resistant to those things if you ate all your meat raw. Are other animals affected by food poisoning to any significant degree?
Your gut flora would probably be completely different and more resistant to those things if you ate all your meat raw.
AFAIK, the immune system has some ability to adapt to different pathogens, but this doesn’t mean that eating significant quantities of raw meat wouldn’t pose a health risk, particularly for a long-lived species such as humans.
Are other animals affected by food poisoning to any significant degree?
AFAIK, trichinellosis is endemic in wild carnivorous mammals.
You should also account for how myelinated the neurons are, and how many of them are not myelinated at all, since this affects neuron size and energy expenditure a lot.
Without myelin, the conduction speed of a neuron is mainly determined by its diameter. Some animals don’t have myelin at all, and their neurons can be huge because of this reason. I’m not sure if this applies to rodents, but it would explain why their neurons grow in size as the brain grows, because conduction distances grow too, and therefore you need a higher conduction speed, and this can only be achieved by having a larger neuron. Even humans have some neurons that are not myelinated, and they vary from this to highly myelinated with anything in between and their conduction speeds vary in proportion.
Connection count should also be an important factor, and it can vary by many orders of magnitude. It also matters how many neurons are active at a time.
ETA: removed it. Nutrition is the mind-killer.
Sources:
Axonal conduction delays
Principles underlying mammalian neocortical scaling
There’s another thing to consider, which is that myelination requires special glial cells around axons to actually provide the myelin sheath, and these cells are relatively large themselves and use up energy. Glia (both for myelin and many many other functions) actually take up a large fraction of the space of the human brain and there are (by some estimates) 10x more glia than neurons in the human brain. The human brain especially has a lot of glia (90% of brain tissue) whereas for a mouse it’s only 65% of brain tissue.
At last, a reply to the interesting stuff! :)
IIRC myelinated neurons are both more energy efficient taking into account the glial cells and take less space than nonmyelinated neurons if we talk about similar conduction velocities. I’ll have to check this one just to be sure.
You mean the volume or the number of cells? This is certainly interesting and supports my hypothesis of why rodent neurons grow in size as their brains grow. What do you think?
Why are some brains less myelinated than others? Was their evolution just less lucky?
Possibly, but I’d caution against simplistic evolutionary arguments; evolution is rarely so simple. For instance, chimpanzees have higher axon myelination during development and adulthood than human brains do.
Perhaps they’re the lucky ones in that particular case. We really can’t assume our brains are the most efficient in all respects.
A raw food diet that a modern consumer with access to supermarkets and kitchen equipment might try would not resemble a raw diet in pre-agricultural times. Most raw food diets strongly recommend juicing, blending, mixing, etc. which are essentially pre-digestion. Furthermore, they’re also generally billed as “weight loss diets,” allowing sedentary people to lose weight without exercising—the calorie total might be in the 1000-1500 range.
Cooking greatly increases how many things you can eat, what’s safe to eat, and how many calories you can fit into your stomach. Cooking might decrease nutrient absorption by 5-10%,but when you can eat 50-100% more, it’s a fine trade.
I think you guys are just privileging a cool hypothesis a neuroscientist is making about gastroenterology. It’s pretty weird and frustrating how many objections this single point is getting, given that just like I already said, it’s very testable.
So is chewing and it works just fine.
Who’s doing the billing? Are these people fat to begin with? Where are you getting these numbers from and do they really have anything to do with the foodstuff being raw?
Most foods you can make safe by cooking do not comprise a great deal of what people eat. Some of them could be unsafe raw just because human GI tracts are used to cooked food by now. Also, most foods don’t significantly shrink when you cook them.
Again, where are you getting these numbers from?
Are you familiar with raw food diets? Could you point to one? In particular, where do the bulk of the calories come from?
I can’t say I’m familiar with them, although I’ve occasionally eaten very little cooked food. Bulk of the calories could come from fish, milk, eggs, nuts, fruit and vegetables. Fish and eggs carry a risk of food poisoning if you don’t know your source. So does red meat.
It’s possible that this wouldn’t be a significant problem if your GI-tract and immune system were used to these kinds of threats however. It’s also possible that bacteria causing food poisoning are more potent and more common than they used to be or than they are in nature.
Living on a raw food diet when you don’t have to do your own hunting and gathering might have a different energy balance.
Could be so, but that’s idle speculation and I’d still test the hypothesis before accepting it :)
Are there any pre-modern societies which live on raw food?
Requesting a data point: did your heuristics point to me being a proponent of raw foodism and trying to sneak in my ideology? I hadn’t even read about it before I made my comment.
I don’t encounter many people in my life who care about particular diets much and count myself amongst them. In fact, I know none irl. Do you find this unusual?
I didn’t assume you were a raw food proponent.
I don’t know a lot of people who do much with their diet. Offhand, I know two ex-vegetarians who still eat very little meat, one person who did CR for a few years, and one person who gave himself an eating disorder (I hope he’s over it) by following a claimed-to-be- healthy diet which was much too low calorie for him. Oh, and a woman who seems to be doing well on the same diet. And two people who are following some complicated diet which involves different types of food on a cycle. They’ve lost weight, but I’m dubious about their ability to maintain it. Rather more people than I thought before I started listing.
I know two people who are serious about supplements. One of them limits carbs drastically.
“Nutrition is the mind-killer.” Definitely true, and funny.
I’ve done a little survey about the effects of trying to lose weight, if you’d like to see some mind-killing and some non-mind-killed people. I’m trying to figure out how to deal with (other people’s) compulsion to give advice. Forbid it, or let it roar?
I’m not sure why there not being any would tell us anything, because cooking is common knowledge everywhere by now, and there are other reasons to cook food than nutrition.
That only suggests that peripheral neurons should grow with body size, not neurons in the brain. I suppose that it’s simpler to let central and peripheral neurons be the same size, but that doesn’t seem to me like a good reason.
Why? If the brain is bigger, so are the distances within it.
Do you have a source for the quantitative variation of myelination between vertebrates, and not just the binary question of some have it (vertebrates), some don’t?
Do you have a source for connection count varying between species?
Here’s evidence that axonal diameter grows as brains grow, and that axonal diameter is important for conduction speed.
If you read that article, you will realize that the degree of myelination in a species will depend on how fast conduction they need, since if conduction speed is not taken into account, nonmyelinated fibers are much cheaper to have.
I didn’t have a source at hand for variation of connection count, but found this.
“The neocortex undergoes a complex transformation from mouse to whale. Whereas synapse density remains the same, neuron density decreases as a function of gray matter volume to the power of around −1/3.”
This means that synapse count per neuron varies considerably between species.
A public version of the third link
Thanks.
Do they?
(the Wikipedia section refers to raw vegan diets, but I suppose that eating significant quantities of raw meat, fish or dairy poses a risk of infection by bacteria or worms)
Your gut flora would probably be completely different and more resistant to those things if you ate all your meat raw. Are other animals affected by food poisoning to any significant degree?
AFAIK, the immune system has some ability to adapt to different pathogens, but this doesn’t mean that eating significant quantities of raw meat wouldn’t pose a health risk, particularly for a long-lived species such as humans.
AFAIK, trichinellosis is endemic in wild carnivorous mammals.
It definitely poses a risk, but how high is it?
The question is, do they actually suffer from it, or are they carriers.