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human temperature
Maybe I heard an answer on QI but are there certain reasons behind why the human temperature evolved to be around 98.6.
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Several factors will be involved here.
If bodies had evolved to be much hotter, then they would have to evolve even greater insulation to combat heat loss in cool conditions.
Enzyme reactions are also a deciding factor because an increase in the temperature increases the rate of bodily chemical reactions, but if it gets too hot, enzymes become denatured.
Another factor is what rate of metabolism is required by the organism. Birds require a greater rate than mammals in order to sustain flight and they have consequently evolved a slightly higher body temperature than us (105�F, 40�C).
If bodies had evolved to be much hotter, then they would have to evolve even greater insulation to combat heat loss in cool conditions.
Enzyme reactions are also a deciding factor because an increase in the temperature increases the rate of bodily chemical reactions, but if it gets too hot, enzymes become denatured.
Another factor is what rate of metabolism is required by the organism. Birds require a greater rate than mammals in order to sustain flight and they have consequently evolved a slightly higher body temperature than us (105�F, 40�C).
In simple terms, the types of enzymes in the human body work most efficiently at around 98.6 degrees F or 37 degrees C. This has therefore become the optimum temperature for chemical reactions to occur in the human body. Enzymes play a part in thousands of chemical reactions in the body.
Having said that, it's wrong to think that anything outside 98.6 is abnormal. Scientists tend to speak nowadays of a body temperature range rather than that 98.6 figure. As long as your body temperature falls within the range of from about 97.5 to 98.8, everything is considered OK. The medical profession in the UK widen the parameters further by usually not considering anything between 96 and 104 as being life-threatening, except in the case of infants and young children. Enzymes quite happily perform their functions within this range although not necessarily at optimal efficiency at the two extremes.
Once you go out of this range, many symptoms begin to occur due to inactivation or suppresion of enzyme activity. These will include changes in blood pressure, respiratory rate, pulse rate, blood viscosity and hundreds of others. If the body core temperature is drastically outside it's normal range for a prolonged period, organ damage occurs which leads ultimately to fatality.
Infections cause the body to release chemicals which increase the core temperature. This is one reason why infections iinvariably cause fever. Under normal circumstances, these chemicals play a key part in the thermoregulation of the body allowing the core temperature to rise or fall.
Having said that, it's wrong to think that anything outside 98.6 is abnormal. Scientists tend to speak nowadays of a body temperature range rather than that 98.6 figure. As long as your body temperature falls within the range of from about 97.5 to 98.8, everything is considered OK. The medical profession in the UK widen the parameters further by usually not considering anything between 96 and 104 as being life-threatening, except in the case of infants and young children. Enzymes quite happily perform their functions within this range although not necessarily at optimal efficiency at the two extremes.
Once you go out of this range, many symptoms begin to occur due to inactivation or suppresion of enzyme activity. These will include changes in blood pressure, respiratory rate, pulse rate, blood viscosity and hundreds of others. If the body core temperature is drastically outside it's normal range for a prolonged period, organ damage occurs which leads ultimately to fatality.
Infections cause the body to release chemicals which increase the core temperature. This is one reason why infections iinvariably cause fever. Under normal circumstances, these chemicals play a key part in the thermoregulation of the body allowing the core temperature to rise or fall.
Hi prof, I think you have rather assumed a fait accompli in your answer where the enzyme balance has already evolved to be at an optimum efficiency at 37C. The question was why it evolved to be that temperature in the first place. I tried to suggest some of the factors that led this to happen.
Firstly, why did warm bloodedness evolve at all? Warm blood gave predators a speed advantage over cold-blooded prey in a cool environment. Warm blood gave prey organisms an advantage by being able to rapidly escape. The downside is that extra fuel is needed to produce and maintain this higher temperature. The higher the temperature, the more fuel will be needed which is a disadvantage unless there is an overabundance of food - even then, there is a limit to how quickly the food can be digested to provide energy. Natural selection therefore selects fo a compromise, not too cold as to have a mobility disadvantage, and not too hot so as to require such a great food input that it would put the organism at risk of starvation in periods of adversity.
There is no reason why an enzyme mixture balaced to work at an optimum temperature higher than 37C. As I pointed out, birds have evolved a temperature of 40C because they need a faster metabolism and reactions go faster at higher temperatures. Far more extreme examples of enzymes evolving to be balanced at much higher temperatures can be found in the organisms living in geothermal springs and around submarine smoker vents. Such organisms though do not have to generate the heat, just survive in it.
It is all a trade-off between ADvantages and DISadvantages.
Firstly, why did warm bloodedness evolve at all? Warm blood gave predators a speed advantage over cold-blooded prey in a cool environment. Warm blood gave prey organisms an advantage by being able to rapidly escape. The downside is that extra fuel is needed to produce and maintain this higher temperature. The higher the temperature, the more fuel will be needed which is a disadvantage unless there is an overabundance of food - even then, there is a limit to how quickly the food can be digested to provide energy. Natural selection therefore selects fo a compromise, not too cold as to have a mobility disadvantage, and not too hot so as to require such a great food input that it would put the organism at risk of starvation in periods of adversity.
There is no reason why an enzyme mixture balaced to work at an optimum temperature higher than 37C. As I pointed out, birds have evolved a temperature of 40C because they need a faster metabolism and reactions go faster at higher temperatures. Far more extreme examples of enzymes evolving to be balanced at much higher temperatures can be found in the organisms living in geothermal springs and around submarine smoker vents. Such organisms though do not have to generate the heat, just survive in it.
It is all a trade-off between ADvantages and DISadvantages.
Much of what you've said is true gen2 and I'd be the first to agree that I could have made a better job of the answer.
If you could just return to my previous answer for the moment and point out to me where I stated that enzymes had already evolved to work at these optimum temperatures prior to the physiological and biochemical maturity of the organism, I'd be very grateful as I can't find it. If you could point it out, I might be able to see the fait accompli for myself.
You did an excellent job in summarising the salient points in your first answer, but regretfully, I did not see your post before I posted mine.
You've provided a good summary of of the reasons why endotherms evolved although I think the relevance of hibernation in endotherms should have been mentioned. It's not all about speed advantage, escape and metabolic energy efficiency as you know yourself.
I think you may have made a typo or omission in the first sentence of your penultimate paragraph as the meaning is not immediately clear. Either way, as you know, enzymes do function best at their optimum temperatures - I'm sure you've seen the typical graphs. I implied that enzymes are in general quite forgiving regarding moderate temperature variation outside their optimum functioning temperature and this is true. As you know, enzyme efficiency decreases outside this optimum temperature and you pointed out the relevance of heat to denaturation. However, let's not forget that cold decreases the molecular activity of enzymes too. Sustained enzyme molecular inactivity can be just as bad for an organism as denaturation.
(continued)
If you could just return to my previous answer for the moment and point out to me where I stated that enzymes had already evolved to work at these optimum temperatures prior to the physiological and biochemical maturity of the organism, I'd be very grateful as I can't find it. If you could point it out, I might be able to see the fait accompli for myself.
You did an excellent job in summarising the salient points in your first answer, but regretfully, I did not see your post before I posted mine.
You've provided a good summary of of the reasons why endotherms evolved although I think the relevance of hibernation in endotherms should have been mentioned. It's not all about speed advantage, escape and metabolic energy efficiency as you know yourself.
I think you may have made a typo or omission in the first sentence of your penultimate paragraph as the meaning is not immediately clear. Either way, as you know, enzymes do function best at their optimum temperatures - I'm sure you've seen the typical graphs. I implied that enzymes are in general quite forgiving regarding moderate temperature variation outside their optimum functioning temperature and this is true. As you know, enzyme efficiency decreases outside this optimum temperature and you pointed out the relevance of heat to denaturation. However, let's not forget that cold decreases the molecular activity of enzymes too. Sustained enzyme molecular inactivity can be just as bad for an organism as denaturation.
(continued)
If you are stating that there's no reason why a mixture of enzymes should not have an optimum temperature of higher than 37C, you're absolutely right and again we are in agreement. Such enzyme combinations do exist. I couldn't have said anything to the contrary in my earlier post as I did not even discuss this aspect of enzymology.
As far as birds are concerned, there are some modifications in their enzyme structures to accomodate their increased body temperatures in comparison to other endotherms. Without these modifications, increased metabolism would be somewhat difficult.
When we come to discuss organisms living in extremes of temperature in geothermal springs and submarine smoker vents, the biochemical adaptions are considerable in order for the organism to survive. As you're aware different groups of enzymes have evolved in order to allow these organisms to survive and a number of endotherm enzymes do not occur in organisms living at extreme temperatures due to their inability to function.
Perhaps I should not have confined myself to Homo sapiens in my first post.
As far as birds are concerned, there are some modifications in their enzyme structures to accomodate their increased body temperatures in comparison to other endotherms. Without these modifications, increased metabolism would be somewhat difficult.
When we come to discuss organisms living in extremes of temperature in geothermal springs and submarine smoker vents, the biochemical adaptions are considerable in order for the organism to survive. As you're aware different groups of enzymes have evolved in order to allow these organisms to survive and a number of endotherm enzymes do not occur in organisms living at extreme temperatures due to their inability to function.
Perhaps I should not have confined myself to Homo sapiens in my first post.
Hi prof, You ask where you stated that enzymes had already evolved to work at these optimum temperatures. You did not state it in as many words but that was implied by your first paragraph. Claret1 asked why the human temperature evolved to be around 98.6�F and the meaning I take from your first paragraph is that it is at that temperature because that is the optimum temperature of body enzymes. ie The enzymes came first and the body temperature followed. To quote:
"In simple terms, the types of enzymes in the human body work most efficiently at around 98.6 degrees F or 37 degrees C. This has therefore become the optimum temperature for chemical reactions to occur in the human body. Enzymes play a part in thousands of chemical reactions in the body."
My point is that the human body could have settled at a different temperature with a different set of enzymes and went on to show that that was possible with examples. I also suggested some of the driving forces that led it to finish up around 37�C for humans.
I accept I made a typo in my penultimate paragraph. The first sentence should have read:
"There is no reason why evolution cannot produce an enzyme mixture balaced to work at an optimum temperature higher than 37�C."
Anyway, let us not quibble. Between us, I think claret1 has received a fuller answer than he/she was expecting.
"In simple terms, the types of enzymes in the human body work most efficiently at around 98.6 degrees F or 37 degrees C. This has therefore become the optimum temperature for chemical reactions to occur in the human body. Enzymes play a part in thousands of chemical reactions in the body."
My point is that the human body could have settled at a different temperature with a different set of enzymes and went on to show that that was possible with examples. I also suggested some of the driving forces that led it to finish up around 37�C for humans.
I accept I made a typo in my penultimate paragraph. The first sentence should have read:
"There is no reason why evolution cannot produce an enzyme mixture balaced to work at an optimum temperature higher than 37�C."
Anyway, let us not quibble. Between us, I think claret1 has received a fuller answer than he/she was expecting.
Hi gen2
Yes, that first paragraph of mine could have been better phrased and I can see in hindsight that it may have been misunderstood to mean something other than I intended.
Rest assured, as an academic, assuming faits accomplis is not something I do on a regular basis and I apologise unreservedly if you've read it that way. It was not meant to come across like that.
Yes indeed, the human body could have settled at a different temperature with a different set of enzymes and we've both said as much.The environments you cited were ideal to illustrate the point.
As to the typo, I'm glad I interpreted the gist of the sentence in the first sentence of my last post and I'm totally in agreement with you.
Thanks for pointing out my error. It's very humbling to realise that it's all very well me pointing out errors to undergrads, postgrads, lecturers and all the other grades in my department when perhaps it's not a bad idea that I get my own wrists slapped now and again. Honestly, It's much appreciated gen2.
Thanks again.
Yes, that first paragraph of mine could have been better phrased and I can see in hindsight that it may have been misunderstood to mean something other than I intended.
Rest assured, as an academic, assuming faits accomplis is not something I do on a regular basis and I apologise unreservedly if you've read it that way. It was not meant to come across like that.
Yes indeed, the human body could have settled at a different temperature with a different set of enzymes and we've both said as much.The environments you cited were ideal to illustrate the point.
As to the typo, I'm glad I interpreted the gist of the sentence in the first sentence of my last post and I'm totally in agreement with you.
Thanks for pointing out my error. It's very humbling to realise that it's all very well me pointing out errors to undergrads, postgrads, lecturers and all the other grades in my department when perhaps it's not a bad idea that I get my own wrists slapped now and again. Honestly, It's much appreciated gen2.
Thanks again.
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