Quick Biology Question

[Zaarin]

In my fantasy IP, elves have a higher average body temperature of ~105°F (or 44.5°C), with a correspondingly higher metabolism. Biology not really being my strong suit, are there other implications of this that I should be thinking about? A few things I have considered:

• Elves require a higher caloric intake than humans and higher fluid intake. More frequent rest periods?

• Elves would be better sprinters but poorer marathon runners (i.e., greater quick bursts of energy, poorer endurance).

• Humans feel cold to elves; elves feel fevered to humans.

• Elves probably have a greater heat tolerance, poorer cold tolerance.

• Elves should probably have higher blood pressure. Thinner blood? Modifications to the heart?

[Pabappa]

ive edited this post several times as i often do so some of looks a bit jumbled, sorry ...

Humans feel cold to elves; elves feel fevered to humans.

This one is for sure.

Elves probably have a greater heat tolerance, poorer cold tolerance.

Sure, but not by much ... the temperature gap isnt really much compared to what we deal with outside. The intense shivering people feel during fevers is because the body is shivering to raise its core temperature ... but a person who was at 105F all the time wouldnt need to shiver. Basically Id just say their preferred temperature scale would be shifted upward by 6 degrees Fahrenheit, which is well within the range of humans' natural variation.

The elves might be immune to a lot of diseases that hurt humans, so long as the pathogens carrying the diseases can survive at 98F but not at 105F. (That's what fever is for, after all.) So they might never get a flu. On the other hand, if their biology is the same as Earth's, they have less room to move upward when they get a disease that can tolerate those temperatures .... even a mild fever for the Elves would cause instant and irreversible brain damage.

In fact, they might even be more heat-prone then we are, since at least when we get heatstroke we have early warning signs that we're being overheated and plenty of room to let our body temperatures rise before the brain damage begins. Whereas these elves, if they work on a hot day, will begin to suffer permanent damage if their body temperature rises even a little bit. Thus, they would have to either deal with that, or evolve some mechanism that prevents the body temperature from rising, which could make them quite vulnerable in hot environments.

Also, I dont think people with fast metabolisms need more sleep, if thats what you meant by rest. I have a very fast metabolism myself but I dont have trouble with an 8-hr sleep schedule and I dont think other people with fast metabolisms generally do either. (we'd have noticed by now.)

[mèþru]

they have less room to move upward when they get a disease that can tolerate those temperatures .... even a mild fever for the Elves would cause instant and irreversible brain damage.

In fact, they might even be more heat-prone then we are, since at least when we get heatstroke we have early warning signs that we're being overheated and plenty of room to let our body temperatures rise before the brain damage begins. Whereas these elves, if they work on a hot day, will begin to suffer permanent damage if their body temperature rises even a little bit. Thus, they would have to either deal with that, or evolve some mechanism that prevents the body temperature from rising, which could make them quite vulnerable in hot environments.

If their scale is shifted six degrees, shouldn't that mean they can have higher temperatures than humans but human lows are even more dangerous for them?

[Pabappa]

Theyll be vulnerable to hypothermia at temperatures slightly milder than those that would affect humans, yes .... but 6°F is really not a lot. And having thought about it as I wrote, I don't think they'd be more heat-hardy either, because they can't temporarily raise their temperature to adjust to hot conditions as we can. An elf working heavy labor outdoors on a hot day might simply faint.

To put another way, i think the brain damage at ~106F is a hard limit, and to change that, one would need to change the way brain chemistry works.

[Salmoneus]

In my fantasy IP,

"IP"?

elves have a higher average body temperature of ~105°F (or 44.5°C), with a correspondingly higher metabolism. Biology not really being my strong suit, are there other implications of this that I should be thinking about?

Well, three particularly striking implications spring to mind:

1. They're birds. Mammals have lower body temperatures, and generally within a very narrow range - I found a chart of common farmed mammals, and the temperatures vary between 38 and 40 degrees, with the latter only for young and/or small animals; chickens, like other birds, are a few degrees hottter. The big exception to this is apparently camels, who, it seems, aren't fully warm-blooded - that is, they don't fully regulate their temperature, and it can vary considerably (34-42, apparently) depending on environmental temperature and water availability, presumably as an extreme specialist adaptation to desert environments.

2. They're smaller than humans. Generally, for a given class (in a loose sense, mammal, reptile, etc), body temperature is inversely proportional to size.

3. They're short-lived. Body temperature is obviously inversely associated with life expectancy.

A few things I have considered:

• Elves require a higher caloric intake than humans and higher fluid intake. More frequent rest periods?

To maintain a higher heat, they'll need a higher metabolism, and thus will either have to consume more calories or else expend fewer for other purposes. That could indeed mean more rest periods - some animals with high temperatures go into periodic torpor, where their temperatures drop to something more maintainable.

• Elves would be better sprinters but poorer marathon runners (i.e., greater quick bursts of energy, poorer endurance).

I'm not sure that's true at all. I guess it's true they'd be bad in the marathon - high metabolism and higher starting temperature are obviously handicaps. But I don't think they'd be better at sprinting - I don't think blood temperature would make a difference there. It's much more about muscle mass, muscle distribution, and muscle type. Indeed, as they must 'work harder' just to keep so hot, it may be they'd be worse at anaerobic tasks. I mean, if your cells are working at 50% before you start sprinting and mine are working at 75%, you have more capacity to hand to spare for sprinting than I do. On the other hand, it's true that you might find it hard to raise your %, and I might be able to repurpose mine by switching to sprinting and letting waste heat do the job of maintaining temperature, so...

• Humans feel cold to elves; elves feel fevered to humans.

Assuming the same sort of skin/fur/feathers/sweat etc, yes.

• Elves probably have a greater heat tolerance, poorer cold tolerance.

I'm not sure that's true. Poorer cold tolerance, sure - they become exhausted by trying to maintain their temperature quicker. But they may also have worse heat tolerance, because they're closer to the thresholds - brains, muscles, and the reproductive systems all hit hard limits on temperature. If you start off hotter than me, you'll probably overheat before I do!

• Elves should probably have higher blood pressure. Thinner blood? Modifications to the heart?

I'm not sure this is necessarily true. To maintain their higher metabolism, they'll need higher VO2, and that could mean higher blood pressure - but it could also mean higher circulatory speed, higher blood volume, or increased oxygen density in blood.


I think the big question here might be: why? What benefit do elves get from all of this?

[zompist]

If this is another planet, some of the assumptions here may change. E.g. if normal body temperature is 6° higher, it seems reasonable that their brains can withstand higher temps also.

It might help to think about the ancestral environment. We're already adapted to hot climates-- we're savannah animals. The other apes are not; they're forest animals. Where do the elves live, and why do they need that extra heat?

Oh, and we're adapted to running down prey in the savannah, for enormous distances. That's why we're nearly hairless: that, and our copious sweat glands, allow for fast heat dissipation while running. If you wanted (say) the traditional forest elves, they should really be covered with fur...

More energy might well mean more brains. Humans have bigger brains than other apes, and this is very likely due to cooking, which makes both plant and animal nutrients more easily available. Apes have to eat all day just to maintain their small brains. (So I'd be skeptical if, say, your elves turn out to eat nothing but raw plants. Where are they getting the energy from?)

[Zaarin]

The elves might be immune to a lot of diseases that hurt humans, so long as the pathogens carrying the diseases can survive at 98F but not at 105F. (That's what fever is for, after all.) So they might never get a flu. On the other hand, if their biology is the same as Earth's, they have less room to move upward when they get a disease that can tolerate those temperatures .... even a mild fever for the Elves would cause instant and irreversible brain damage.

Well, my setting is based on a combination of Ptolemaic and Ancient Near Eastern cosmology, so diseases are actually caused by evil spirits, but I did have in mind that elves are more resistant to disease so it's nice that there would be a real-world reason for it as well.

Also, I dont think people with fast metabolisms need more sleep, if thats what you meant by rest. I have a very fast metabolism myself but I dont have trouble with an 8-hr sleep schedule and I dont think other people with fast metabolisms generally do either. (we'd have noticed by now.)

Well, I was kind of thinking of cats, who have a body temperature just a few degrees cooler, but I'm sure there are also other factors that make cats' habits different than ours.

An elf working heavy labor outdoors on a hot day might simply faint.

That actually ties in nicely with my conception of the elves as being more "domestic" and stay-at-home and less hardy and adventurous than humans.

To put another way, i think the brain damage at ~106F is a hard limit, and to change that, one would need to change the way brain chemistry works.

Well, with my altered cosmology, I can probably do that too...

In my fantasy IP,

"IP"?

"Intellectual property"--short hand for everything related to world building.

elves have a higher average body temperature of ~105°F (or 44.5°C), with a correspondingly higher metabolism. Biology not really being my strong suit, are there other implications of this that I should be thinking about?

Well, three particularly striking implications spring to mind:

1. They're birds. Mammals have lower body temperatures, and generally within a very narrow range - I found a chart of common farmed mammals, and the temperatures vary between 38 and 40 degrees, with the latter only for young and/or small animals; chickens, like other birds, are a few degrees hottter. The big exception to this is apparently camels, who, it seems, aren't fully warm-blooded - that is, they don't fully regulate their temperature, and it can vary considerably (34-42, apparently) depending on environmental temperature and water availability, presumably as an extreme specialist adaptation to desert environments.

2. They're smaller than humans. Generally, for a given class (in a loose sense, mammal, reptile, etc), body temperature is inversely proportional to size.

3. They're short-lived. Body temperature is obviously inversely associated with life expectancy.

I feel like with my non-Einsteinian physics I can probably handwave your first two points a little (I imagine elves being slightly shorter than humans on average, but we're talking a few inches difference, not Keebler elves). I could probably work with the third (probably offset a little by the above-mentioned resistance to disease and lower proclivity to violence).

A few things I have considered:

• Elves require a higher caloric intake than humans and higher fluid intake. More frequent rest periods?

To maintain a higher heat, they'll need a higher metabolism, and thus will either have to consume more calories or else expend fewer for other purposes. That could indeed mean more rest periods - some animals with high temperatures go into periodic torpor, where their temperatures drop to something more maintainable.

Makes sense.

• Elves would be better sprinters but poorer marathon runners (i.e., greater quick bursts of energy, poorer endurance).

I'm not sure that's true at all. I guess it's true they'd be bad in the marathon - high metabolism and higher starting temperature are obviously handicaps. But I don't think they'd be better at sprinting - I don't think blood temperature would make a difference there. It's much more about muscle mass, muscle distribution, and muscle type. Indeed, as they must 'work harder' just to keep so hot, it may be they'd be worse at anaerobic tasks. I mean, if your cells are working at 50% before you start sprinting and mine are working at 75%, you have more capacity to hand to spare for sprinting than I do. On the other hand, it's true that you might find it hard to raise your %, and I might be able to repurpose mine by switching to sprinting and letting waste heat do the job of maintaining temperature, so...

Again I was looking at cats as a model, which may be a misleading model.

• Humans feel cold to elves; elves feel fevered to humans.

Assuming the same sort of skin/fur/feathers/sweat etc, yes.

Externally they look like humans, so yes.

• Elves should probably have higher blood pressure. Thinner blood? Modifications to the heart?

I'm not sure this is necessarily true. To maintain their higher metabolism, they'll need higher VO2, and that could mean higher blood pressure - but it could also mean higher circulatory speed, higher blood volume, or increased oxygen density in blood.

Makes sense.

I think the big question here might be: why? What benefit do elves get from all of this?

Well, from an out of universe standpoint, it was a way to make elves and humans, who externally look pretty close to indistinguishable from each other, a discomforting sense of alienness regarding each other (in addition to the fact that elves can use magic and humans cannot). I also imagined magic, which is generated from a physical organ inside the elf's body, requiring additional blood flow, much like the brain does.

If this is another planet, some of the assumptions here may change. E.g. if normal body temperature is 6° higher, it seems reasonable that their brains can withstand higher temps also.

Well, like I said above, the cosmology of this world is significantly different from ours: it's flat, with a 60,000 ft acacia tree holding up a literal crystaline dome of the firmament...But I do like to maintain a certain level of verisimilitude in smaller things.

It might help to think about the ancestral environment. We're already adapted to hot climates-- we're savannah animals. The other apes are not; they're forest animals. Where do the elves live, and why do they need that extra heat?

Oh, and we're adapted to running down prey in the savannah, for enormous distances. That's why we're nearly hairless: that, and our copious sweat glands, allow for fast heat dissipation while running. If you wanted (say) the traditional forest elves, they should really be covered with fur...

My entire setting is based heavily on the Ancient Near East, so much (but not all) of the land they occupy is hot and arid to a greater or lesser degree. (Not all desert, of course, just as not all of the Near East is desert, contrary to the popular imagination...)

More energy might well mean more brains. Humans have bigger brains than other apes, and this is very likely due to cooking, which makes both plant and animal nutrients more easily available. Apes have to eat all day just to maintain their small brains. (So I'd be skeptical if, say, your elves turn out to eat nothing but raw plants. Where are they getting the energy from?)

Their diet is perfectly comparable to a Bronze Age human's. (My elves have nothing much in common with either standard fantasy elves or Tolkien's Elves--they are neither immortal nor long lived, for instance. I actually use the name due to a linguistic coincidence from one of the elves' main language families, wherein /ʔeˈloːb/ means "person.")