Body Heat

[ed84c]

I was at Autosport international on saturday, and rather warm from the amount of people wandering about.

 

Every the stickkler for efficiency I was wondering; Would it not be more efficient to have a cooler body temp, slowing things down, but evelotunarily speaking it would mean that there would be less energy wasted creating heat.

[5614]

our internal organs and microorganisms, namely enzymes need that temp to survive... if we change out body temp enzymes and bacteria would die.

[ed84c]

no technically i believe they would just work more slowly.

[Tesseract]

Do the people that live in isolated cold areas such as northern Canada and Syberia have higher or lower body temps?

[5614]

they have the same temps... as do ALL humans.

[Mokele]

Yes, having a lower body heat *would* make us more efficent. We would use less than 1/10th of the energy we do now, and need to eat approximately 1/20th as much, if we maintain the same activity level. However, without burning food to make heat to keep ourselves warm, movement would be the main source of energy consumption, so by simply not moving, you could cut your already lowered energy consumption by at least a factor of 3.

 

Welcome to the amazing efficiency that is Reptilia and Amphibia. There's a reason that your average endotherm only converts 2% of the biomass it takes in into new biomass (growth or reproduction), versus an average of 50% for herps (reptiles and amphibians).

 

However, like everything, there's trade-offs. Ectotherms pay for this efficiency by becoming, in effect, slaves to the sun. Most are dinurnal, and all have to spend a significant amount of time thermoregulating to maintain their body temperatures. They can exploit niches that mammals cannot, becuase as mammals get smaller, it costs more and more to maintain a stable temperature, yet reptiles suffer no such metabolic barrier to miniaturization. Also, mammals can exploit colder climates than herps. But herps have a far greater mastery of the water, due to their greatly reduced oxygen requirements.

 

The biggest one, though, is aerobic scope. Say you're walking at a slow speed. You can continue to do this for a long, long time, without exhaustion. If you increase your speed a bit, it's the same, no exhaustion. But at a certain point, your body can no longer supply enough oxygen to maintain your metabolism at that speed, and you switch to anaerobic metabolism (at least in part). Now your endurance is substantially lower, and you're vulnerable to cramps. Further increases in speed serve to reduce your endurance more and more. The range up until exhaustion becomes a factor is called your aerobic scope.

 

Now, apparently, aerobic scope is universally 10 times your resting metabolic rate. For organisms with a low resting metabolic rate (like a lizard), that means anything beyond a casual walk is anaerobic, and, while lizards can still move *very* fast, they cannot sustain high-speed activity. In contrast, a human, with a high resting metabolic rate, can run at moderately high speeds and still not have to worry about exhaustion (at least not for a long time). The maximum speeds may be the same, but for intermediate speeds, mammals have a strong endurance advantage. This allows them to function as much more active, wide-ranging animals than reptiles. But they pay the price for it, in terms of increased food requirements.

 

So, basically, each side has advantages and disadvantages, and which outweight the other depends on the ecological niche in question.

 

Mokele

[5614]

no technically i believe they would just work more slowly.

 

technically that is wrong too!

 

([edit] they refers to micro orgranisms!)

 

our body supplies micro organisms with the ideal or optimun temperature to work at, if we changed out internal body temp by a little they wouldnt work as well... however if you make the body temp too high or too low at a certain point they stop working all together.

 

so we're optimised for them, change that a little they dont work as well, change it too much they dont work at all.

[ecoli]

But I believe the question refered how would things be different if we evolved to have a lower body temperatures, not if our body temps changed right now. That's a completely different question.

[ed84c]

yes it was, i thought we would be more efficient

[UCF-Forensic]

hmm. Interesting. I'm not sure how it would effect the nominal physiology of the system, but I do believe that we would probably get sick more often, as you know, body heat rises in response to infection in an attempt to kill thermosensitive microbes. My guess is how much of a change in temperature are we looking at here??

 

I would posit that we would still be generating peaks in temperature while exerting physical force, even when doing something as trivial as meandering around a hallway.

 

My whole take is that biology dictated our body temperature for a reason, and there is no reason why we should think of running any cooler...for all we know, this temperature may be the only thing that has kept us as a species alive....ok that was a bit dramatic, but does anybody else see my point??

 

Open to criticism,

 

~Steve

[Mokele]

but I do believe that we would probably get sick more often

 

Actually, most ecotherms are quite disease-resistant, and handle parasites very well (at least in the wild). Ironicly, their lack of a constant temperature is this strength; pathogens have problems adapting to an environment that, besides trying to kill them via the immune system, has a temperature that fluctuates by up to 20 degrees C.

 

as you know, body heat rises in response to infection in an attempt to kill thermosensitive microbes.

 

Interesting side note: reptiles can get fevers too. When injected with a pyrogen producing bacteria, reptiles spend much more time basking, and maintain their body temperatures at a significantly higher level than usual, until the disease is vanquished. So it's a fever by behavioral thermoregulation rather than hormonal. Neat, huh?

 

I would posit that we would still be generating peaks in temperature while exerting physical force, even when doing something as trivial as meandering around a hallway.

 

Perhaps not something that trivial, but thanks to out large mass, it'd be fairly likely that we could easily maintain a higher than ambient body temp.

 

For an example of this, a recent study showed that large South American rattlesnakes (Crotalus durissus if anyone cares) actually become temporarily endothermic as they digest their meals. The metabolic effort of digesting such a large meal raises their body temperature by as much as 1.5 degrees C. may not sound like much, but for an elongate ectotherm, it's pretty impressive.

 

My whole take is that biology dictated our body temperature for a reason, and there is no reason why we should think of running any cooler...for all we know, this temperature may be the only thing that has kept us as a species alive....ok that was a bit dramatic, but does anybody else see my point??

 

Well, as I noted earlier, endothermy makes up for it's cost with benefits in endurance and maintenance of high activity levels, as well as opening new ecological niches. In another thread (in the evolution forum, the recent one on intelligent aliens), I also point out how endothermy facilitates the evolution of increased brain size (with the roughly correlated increases in intellect).

 

Mokele

[OnlySinan]

Efficiency is relatively optimal in our bodies. This is because as mentioned above: we need this temperature to achieve the optimum state for the functioning of our enzymes.

[Mokele]

Efficiency is relatively optimal in our bodies. This is because as mentioned above: we need this temperature to achieve the optimum state for the functioning of our enzymes.

 

You're confusing the sequence of events. We evolved higher matabolisms (which are extremely inefficient), which resulted in relatively constant, high body temperatures. Our enzymes and protiens adapted to this new temperature, and, as a consequence, we adapted finer temperature control to keep ourselves at that enzymatic optimum.

 

However, compare us to a python, which never had that initial evolution of high metabolism, and we're horribly inefficient. It's protiens are almost as efficient as ours, and keep their properties (though rates are still influenced by temperature) over a huge range of temperatures.

 

In short, that our protiens and enzymes are most efficient at this temperature is merely an adaptation to make us slightly less horribly inefficient, rather than proof of our efficiency. If you expand your scope to compare our efficiency to ectotherms, we're abysmal.

 

Mokele