Getting warmer

Given the topic of this post, suggested by Santiago Verón, I’ve created yet another inadvertent series, so far including Breath of life and But so what. It’s all about that point I made at the start of the blog – that what it feels like to do it isn’t what it is.

This time, it’s warmth, which to be entirely physically accurate, means a discontinuous gradient of heat. The higher side of that discontinuity is “warmer” and the lower, “colder.” In a more boring landscape, there isn’t any sharp discontinuity, and so you really wouldn’t get perceived distinctions of that kind, but in our landscape, or more generally, biosphere, there are all kinds of media through which heat moves, with different densities and conductivities and stuff. Hence, “warmer” and “cooler” are all over the place.

As it happens, at this time I am mighty toasty.

So let’s take that to body temperature, and recognize something that contradicts the casual statements in many biology books: that all living things generate heat. Metabolic action in cells is a heat-producing event, period. In the majority of living creatures, the rate at which this occurs is low enough that the heat in question disperses out of the creature’s body effectively instantaneously. Hence most of the time their body temperature is the same as the location they’re in. This creates the illusion that they are “cold,” because, true, if heat from some new external source comes along, it diffuses in until it’s equilibrated.

The common casual taxonomy of warm-blooded vs. cold blooded is terribly flawed in a lot of ways. I explained one already: a typical living thing is plenty hot, internally, if it’s in a hot place; its blood does not “run cold” in an intrinsic sense. Another problem is using “blood” at all, in that what’s usually meant (a closed circulatory system) is only one of all sorts of ways to deal with internal body fluid. Historically, the whole distinction was socked into a vertebrate-centric view, such that no one called plants, for example, “cold-blooded” although they qualified in full.

All right, let’s get to the real terms. What I’ve been talking about so far, which gram for gram is pretty much every living thing aside from a few outliers, is ectothermy – metabolic heat is passively and invisibly shed, and if more heat comes around, it diffuses in. This contrasts nicely with endothermy: when the creature jacks up its metabolic activity far past the workings of its cells, such that heat cannot be lost as easily and thus builds up in the body. You are warm because the super-produced heat from your cells is backed up at your outer surfaces.

Geeky stuff: this is why increasing metabolism with body size follows an exponential curve instead of a straight line, ’cause the lower your surface-to-volume ratio, the slower the heat leaves. Also, why the dedicated endothermic critters have a higher-placed curve than the dedicated ectotherms, but otherwise it’s the same curve (see the lead graph).

Yes, I bloody well can fly, due to my endothermic wing muscles.

Let’s bring in another variable, in fact, variability in and of itself: how constant is body temperature? Simplistically, one simply ties poikilothermy (variable temperature) to ectothermy, vs. homeothermy (constant temperature) tied to endothermy. It seems to make sense … except that living things refuse to cooperate. Obviously, an ectothermic creature who lives in a constant-temperature environment is ipso facto homeothermic; equally obviously, an endothermic creature who “jacks up” at varying rates and times, or at different rates per body part, is poikilothermic. When you say that, however, physiologists will start screwing up their faces and standing with one foot on the other, because that idealizing of mammals’ and birds’ “high, constant body temperature” vs. nonmammals’ “cold, varying body temperature” is very strong. People just want mammals and birds to be better regulators, that’s all, and they’ll start prattling about so-called “real” homeothermy and similar. There’s even a bogus term heterothermy to try to account for all those inconvenient creatures who dare to generate excess heat without being a bird or mammal, or doing it in the bird/mammal way.

So who does what, again? Well, the overwhelming biomass of living things is straightforwardly ectothermic and (given mostly varying environments) poikilothermic. A few animals leaven that with varying forms of endothermy , and of living animals, two types – mammals and birds – run so hot all the time that they maintain very high, constant temperatures. Let’s explode a myth or two.

  • Endothermic homeotherms live very close to fatal levels of internal body temperature, specifically regarding brain tissue. They are all incredibly vulnerable to environmental heat, and their mechanisms to remove it are themselves grossly energy-costly.
  • Most endothermic homeotherms are vulnerable to hypothermia well above freezing temperatures. The very mechanisms which keep you regulated within a pretty narrow, hot range go all kerflooey just a few degrees colder, and you drop dead even though the cold itself is not damaging your tissues.
  • In areas with very cold, freezing winters, the ectotherms survive nicely, dropping their metabolic rate with the temperature and thus needing little or no food; for them, there is no such thing as hypothermia as long as they don’t actually freeze solid. In those same areas, the endothermic homeotherms die off in droves every winter.
    • I should specify here that hibernation for the one type is very, very different from hibernation for the other.
  • There is nothing “efficient” about endothermic homeothermy. You need insane amounts of food and insane amounts of water, and most of it is pissed away merely in producing heat. These populations are way more subject to size booms and crashes, with the associated risk of dying out in an area, because the resource variables are far more limiting than for ectotherms.

It’s that old vertebrate myth again: that a few heroic “active” types chinned themselves into “world dominance” because they weren’t sluggish, cold, stupid, and confused. As part of scrubbing away that myth, it’s perfectly understandable, to get excited about those big extinct guys called – wait, fair warning: when you say “the dinosaurs” as the general term, then somewhere, a paleontologist breaks into uncontrollable sobs. I’ll have to talk about the right terminology and the fun of how hot their various bodies were in some later post.

FYI, this film is not about endothermy

Whew! All that to set up the context for thinking about how heat has come to be equated with emotions among humans. I probably don’t have to elaborated, as the verbiage is baked in so thoroughly that the list would be epic. I really wonder how that plays out in non-European languages, though.

And then, that’s also tied into the notion of blood, verbally – a hot-blooded murder vs. a cold-blooded murder, a hot-blooded affair, and so on and on. Blood as living, the temperature status of the blood as the “feeling” of the life …

It even gets turned into an ethnic tag for humans, with the notion that “hotter” humans feel emotions more strongly and are more impulsive, when “hotter” seems to refer to the body heat but is specifically tagged toward the local environment. As if by living in a hotter place, you are personally necessarily hotter, and thus your emotions more intense and unregulated … although that’s taking it too literally, as such verbiage invariably ties it to an intrinsic feature of the person’s psychology, no matter where he or she happens to be standing. (Like all well-established racism, it’s ignored when necessary, so one must speak of, for example, Irish pugilism or even subhuman savagery without reference to the Mediterranean heat.)

To glance back toward the broader biology for a bit, you also find the stereotype that an ectothermic creature is necessarily less emotional in some way – whether mellower, duller, (conversely) more calculating, or more contemplative.

Now check this out: Bodily maps of emotions, which is pretty neat imagery material.

But let’s not misread it or be misled by perfervid headlines. It’s not actually a bodily map of emotions at all, but maps of blood temperatures by rather small fractions of degrees. It means that (presuming the subjects’ descriptions of their emotional states are trustworthy, statistically) blood is brought or not brought to various specific places under different emotional regimes. Considering blood is even more watery than your other tissues, it won’t surprise you that it’s a primary transporter of heat, considering, again, small but non-trivial differences. Therefore the images and the data as a whole set are absolutely valid in terms of varying circulation during emotional states, but the heat itself is not the emotion or “where the emotion is.”

[Addendum: Worse even than I thought! They didn’t even measure temperature; along with verbally stating their presumptive mood, the subjects also stated where they felt temperatures to be hot or cool. So there’s no non-socially-mediated data here at all.]

I’ll finish with a a difficult philosophical topic. I hammered in a phrase at the start, about how it feels isn’t actually the thing. Yet … how does that relate to emotions? Especially when you scrub away the romance and consider them to be physiological actions? Or to statements made as sincere commitments?

It’s easy to discount the phrase “just my opinion” even when the statement being made is rock-solid based on what the person has done in the past and is likely to do in the future. It’s almost impossible to discount the phrase “it’s my lived experience” even when the statement being made is quite dubious in terms of what actually happened or will happen. A moment’s thought shows that the precise phrase used is simply not the point at all.

When it comes to breathing, oxygen, blood, and heat, yes, I hope that these posts have shown that we mistake how it feels, specifically, proprioception, vestibular orientation, and interoception, for the biochemistry or other physiology that plays a causal role. But the same principle can be applied to what we think and feel. That is some murky territory to be striding about in. Let’s work with it more, in posts to come.


9 thoughts on “Getting warmer

  1. So what’s the point of being an endothermic homeotherm? And how small or large of a niche is it? How often has it been done (i.e. multiple times, like eyes, or just once)?
    (Is my wording “has it been done” indicative of a deep-rooted false understanding of evolution? It does seem to imply some accomplishment…)


    • “Has it been done” doesn’t ring the alarm for me as (for some reason) I can convert it easily to “has it happened.” The phrase in your post that rings it loud, though, is “what’s the point.” It’s worth reflecting upon, or excavating, in detail.

      Anyway, to endothermic-homeotherm commonality. Just about all living things, now and historically, are ectothermic poikilotherms. All of the Kingdoms except Animalia (pending discovery of endothermy in some cool obscure fungus or protist or something, but I’m not expecting it) – so there’s the overwhelming majority of your terrestrial biomass right there.

      In the animals, I suggest that so-called heterothermy is more common than any textbook says out loud, and that we don’t look hard enough. (If anyone reading this could point me to some hard-working younger prof or maybe to a community/research trajectory I don’t know about, that’d be delightful.) It’s clearly a multiple-origin, evolves all-the-time phenomenon.

      For “warm-blooded” endothermic homeothermy, the only living representatives are birds and mammals. The larger group for which the former are the only living ones displays unequivocal evidence for a variety of endothermic degrees (no pun intended). That seems to be it! That’s a lot of creatures in our daily experience but an extraordinarily small and limited phenomenon in historical and phylogenetic terms. In case I’m not being clear, the overwhelming majority of vertebrates are ectothermic poikilotherms and outside the vertebrates, all or nearly all the rest of the animals.

      I’ve often thought that ectotherms who live in high-and-constant temperature locations are under-studied. There is no reason why any presumed “benefit” or better, feature, that we associate with endothermic homeothermy couldn’t apply to them … unless of course, there is a reason which we don’t know, hence, under-studied.


  2. What would be examples of “ectotherms who live in high-and-constant temperature locations”? Tubeworms living near deep sea hydrothermal vents come to mind, but that’s about it, for me. And do they “harness” the heat or “withstand” it? Problematic wording, I suspect, so let me try to rephrase my question “what’s the point?”: Are there benefits in regard to reproductive success such as endothermic-homeothermic individuals with a higher body temperature being statistically more likely to, say, capture more prey?


    • Tubeworms are the first that came to my mind too, but I’m really referring to much less exotic situations. The temperature doesn’t have to be super-hot or constant every minute, so any of the dozens of high-temp desert creatures would do, during the appropriate season, if they were in the (say) 30-degrees Celsius range most of the time.

      I’d like to know more about the evolutionary history of why birds and mammals can’t tolerate cooling down, either periodically or strategically. Seems like a physiological breakpoint or switch-flip somehow.

      Are there benefits in regard to reproductive success such as endothermic-homeothermic individuals with a higher body temperature being statistically more likely to, say, capture more prey?

      Within a given species, in the context of selective mechanisms – no, there’s no theory-based reason to think so, and no evidence that I know of. That’s another one of those situations in which variables that characterize species and high-level taxonomic differences doesn’t map atomically into the individual-to-individual comparisons and within-species population trends level at which selection operates.


  3. When I saw my name I felt good about myself and showed it to my girlfriend. Thanks.

    I’m having trouble with the end of your post. I get a weird mix of fear and disinterest when I read it, as if I didn’t want to think about how all thought processes are deterministic and at the same time felt it didn’t really change anything or matter. Yet I know there should be a lot to think about and be said, about how, for instance, the same sensations are “repurposed” for heat and anger and shape our view of the world.

    When you refer to emotions as “statements made as sincere commitments”, I’m lost. The following paragraph in full, the second-to-last one, I get on its own but can’t relate it to the rest of the text. And I feel the final question doesn’t puzzle me as much as it should: I read it as “How do we know if we’re feeling the emotions we’re feeling?” to which I would say, we just feel them or sometimes repress them, but there can’t be no confusion because of the nature of feelings. They’re felt.

    I don’t really think all these things. (Well, I do like the “repurposing” part.) But they’re there, getting in the way of my understanding.

    I must concede learning takes time, so I’ll not be in a hurry to get it all at once. But if I could choose one small thing, I would like to ask you about the first phrase I felt confused about. What does it mean “Emotions can be considered statements made as sincere commitments”? The “commitment” part makes me think about commitments towards other people… Since I also have emotions when I’m alone, I don’t get it. (When I read “commitment” all I can think about is telling other people things like “I love you and I always will” or “I swear I’ve never been as angry at someone as I am at you right now”… which is a fitting end to this comment, I think, because it starts and ends with me thinking about my girlfriend ^_^)


    • Hi, and my apologies for the delay in answering.

      The paragraph that you mention really is too much in one small spot. But my topic may be less confusing than it looks. I’m not trying to define emotions in that paragraph. I’m talking about whatever they may be as real phenomena, rather than merely claims. I think it’s fair to say that a claimed emotion may or may not reliable, even if the person believes it to be. So I’m talking only about the times when it is. As for the sentence about commitments, again, I’m not trying to define anything, merely to specify times when it appears that a person is feeling something strongly, and specifying that we can think about those times in which that’s accurate.

      I hope that helps!.


      • Oh I think I get it now! But isn’t that like asking what the program windows in my computer really are? I know they’re electric currents going around a circuit in some way or another. I assumed the same about my “mind” and “soul”, that it’s all electricity and chemical reactions. In the case of computers I assume there are engineers who know the specifics, and in the case of my brain I assume biologists and neurologists haven’t found out the specifics yet.

        That all comes from pop culture, I think. Is that too wrong? Does your question point in another direction, like function? I remember the Pixar movie “Inside Out” and how it says that every emotion serves a purpose, like anger for being treated fairly.


        • This post was really supposed to be about heat, and to show that it is not emotion, even though we associate many emotions with rising body temperature and therefore think that it is.

          Talking about what the emotions themselves are is another issue entirely, and it’s frustrating to discuss. It’s another topic for which I think the science is generally poor, or least not up to the quality I’d expect given 100+ years of formal study. Even the term “limbic system” is a leftover from a completely incorrect model of the brain. We have a better understanding of emotions from an organismal, behavioral perspective than from a neural and hormonal one.

          As for “purpose,” I am comfortable saying that emotions are a subcategory of behavior, and that behavior is subject to evolutionary processes. However, dialogue concerning that is definitely best addressed in later blog posts.


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