# Giant human like 30 to 90 ft tall possible or not

by anas101
Tags: giant, human, tall
P: 3,390
 Quote by anas101 Crowbird. Do you believe that there was Giant human about 15 to 30 ft tall walked on the earth and human become shorter from them?clarify your claim here pleas.

Firstly, we have exactly zero evidence of there being humans this size. So why you keep asking anyone if they believe it and for them to provide evidence is ridiculous.

Secondly, if you want to know the maximum possible size of a human, just do some quick maths.

 Quote by crowbird2 Actually the internal surface area of lungs depends on the sum of the internal surface areas alveoli, (which is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well.) If you increase the size of a human body by N times, The volume of lungs will increase by N^3 times the number of alveoli will also increased by N^3 times. So, the effective gas-exchange surface area will remain proportionately same. Thus there will be no problem breathing.
Now, crowbird2.

Lung volume increases, yes. However, the airway (your throat) only increases in surface area. You hit a point where you cannot get enough air into your lungs (quick enough) due to the effective constriction here. That's your first problem.

I'll try and find the articles I was referring to relating to lung volume, they'll explain what I was attempting to say far better than I could. (Perhaps I've misread it. Regardless, the other factors still stand.)
PF Patron
P: 635
 Quote by crowbird2 Actually the internal surface area of lungs depends on the sum of the internal surface areas alveoli, (which is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well.) If you increase the size of a human body by N times, The volume of lungs will increase by N^3 times the number of alveoli will also increased by N^3 times. So, the effective gas-exchange surface area will remain proportionately same. Thus there will be no problem breathing.
The problem wouldn't be that increasing the size of lungs doesn't increase the surface area of them.

The problem would be with ventilating lungs of those sizes.
 P: 126 I dont know about giant humans, but in the past there have been giant mammals - like giant rhinos http://en.wikipedia.org/wiki/Elasmotherium and in the Cambrian explosion giant insects were living in the world. so there is the possibility of giant humans living on the planet - however, there doesnt seem to be fossil evidence of giant humans as big as you describe (not to my knowledge anyway), and if they did evolve, they would probably not be the same species as us. but you cannot rule out the possibility of giant humans having lived in the past but no fossils having been found, or evolving in the future. physiologically it certainly should be possible - much larger mammals are lving in the world right now, and in the primate group there are bigger species than us. Problems with body size scaling up did not prevent other giant species evolving, so why would the human body plan pose such a hurdle to being scaled up?
 P: 3,390 Can people please stop comparing other species to humans. A rhino is no more a human than a blue whale is. And please keep insects out of it, we're not even close. You can't compare the physiology of a rhino to a human. As I have pointed out many times before, once you get past a certain size you need physiological changes. Period. The question asked by the OP (and later clarified) was relating to current physiology of humans and could they be giant. The answer is that under current conditions we could only get to a certain size and that 30 to 90ft just isn't possible. So no. Now, once again, if you start making physiological changes then anything becomes possible. So it's a moot argument. The OP's question has been answered (many times). Further speculation regarding physiological changes is pointless. We have a) no reason to believe there ever were changes allowing giants and b) no reason to speculate on the future possibility due to the requirement for physiological changes - ergo no longer satisfying the current physiological conditions clause of the question.
PF Patron
P: 635
 Quote by jarednjames Can people please stop comparing other species to humans. A rhino is no more a human than a blue whale is. And please keep insects out of it, we're not even close. You can't compare the physiology of a rhino to a human. As I have pointed out many times before, once you get past a certain size you need physiological changes. Period. The question asked by the OP (and later clarified) was relating to current physiology of humans and could they be giant. The answer is that under current conditions we could only get to a certain size and that 30 to 90ft just isn't possible. So no. Now, once again, if you start making physiological changes then anything becomes possible. So it's a moot argument. The OP's question has been answered (many times). Further speculation regarding physiological changes is pointless. We have a) no reason to believe there ever were changes allowing giants and b) no reason to speculate on the future possibility due to the requirement for physiological changes - ergo no longer satisfying the current physiological conditions clause of the question.

Which is why I said back on the first page, that the changes need to make a "human" 30 feet tall would require they are no longer human
P: 3,390
 Quote by bobze Which is why I said back on the first page, that the changes need to make a "human" 30 feet tall would require they are no longer human
Exactly, the point has been drilled in over and over.
P: 15
 Quote by jarednjames Now, crowbird2. Lung volume increases, yes. However, the airway (your throat) only increases in surface area. You hit a point where you cannot get enough air into your lungs (quick enough) due to the effective constriction here. That's your first problem.
Not clear, please explain a bit more.
The volume of airway will also increase proportionately, so, it is not actually dependent on airway surface area I think.

If you compare 3 feet people with 7 feet, how does your theory of "airway surface area" work there? Children do have small body compared to adults. If your theory is right, adults would have some problem in breathing.
P: 21,687
 Quote by crowbird2 The volume of airway will also increase proportionately, so, it is not actually dependent on airway surface area I think.
Cross section grows like size2, and amount of air that can be transferred depends on cross section, not the volume. That is, it is possible to transfer relatively larger amount of air through the same cross section, but it requires faster flow of the air and larger pressure difference to drive the process, so you hit some limit sooner or later.

 If you compare 3 feet people with 7 feet, how does your theory of "airway surface area" work there? Children do have small body compared to adults. If your theory is right, adults would have some problem in breathing.
Not necessarily, it is enough that kids have some excess capacity that they don't need, but that will be right when they grow up. I am not sure about airway, but if you take a look at puppies, they have disproportionately thick legs - that's example of the excess I am talking about.
P: 3,390
 Quote by crowbird2 Not clear, please explain a bit more. The volume of airway will also increase proportionately, so, it is not actually dependent on airway surface area I think.
Volume of a 'pipe' is irrelevant when it comes to flow rate - in so far as length goes. A longer pipe does not mean a higher flow rate.

What matters here is how much the face area of the wind pipe increases with body height, not the overall volume due to length increases (in fact, length increases wouldn't help things either).
 If you compare 3 feet people with 7 feet, how does your theory of "airway surface area" work there? Children do have small body compared to adults. If your theory is right, adults would have some problem in breathing.
Like I said previously, it doesn't matter between a certain range of heights. There will be a point where the wind pipe face area isn't enough to allow the required amount of oxygen into the lungs.

As you increase a human in size, the lungs increase to the cube. But the airway surface area is a square increase.

You could counter this problem by slowing breathing and taking long, deep breaths, but of course the moment you try to exert yourself and increase your rate of breathing you risk not getting enough oxygen.

If you imagine a bottle being fed by a pipe, you enlarge them both as above, there will be a point where it takes:
a) a significantly longer time for the pipe to fill the bottle to a useable level (in this case the required level of oxygen).
b) a significantly more powerful pump to force the required level into the bottle over the same period.

Even if you had a mix of both the above, it would still only help for a certain period of time. There will eventually come a point where it can't sustain you adequately.
PF Patron
P: 635
 Quote by jarednjames Volume of a 'pipe' is irrelevant when it comes to flow rate - in so far as length goes. A longer pipe does not mean a higher flow rate. What matters here is how much the face area of the wind pipe increases with body height, not the overall volume due to length increases (in fact, length increases wouldn't help things either). Like I said previously, it doesn't matter between a certain range of heights. There will be a point where the wind pipe face area isn't enough to allow the required amount of oxygen into the lungs. As you increase a human in size, the lungs increase to the cube. But the airway surface area is a square increase. You could counter this problem by slowing breathing and taking long, deep breaths, but of course the moment you try to exert yourself and increase your rate of breathing you risk not getting enough oxygen. If you imagine a bottle being fed by a pipe, you enlarge them both as above, there will be a point where it takes: a) a significantly longer time for the pipe to fill the bottle to a useable level (in this case the required level of oxygen). b) a significantly more powerful pump to force the required level into the bottle over the same period. Even if you had a mix of both the above, it would still only help for a certain period of time. There will eventually come a point where it can't sustain you adequately.
Or another experiment you could try Crowbird2 (rather than just an imaginative one) is try breathing through a straw. Like the kind you get at McDonald's.

If you're really healthy you might be able to pull it off for a bit. If that is the case, now go and run around while breathing through the straw
P: 3,390
 Quote by bobze Or another experiment you could try Crowbird2 (rather than just an imaginative one) is try breathing through a straw. Like the kind you get at McDonald's. If you're really healthy you might be able to pull it off for a bit. If that is the case, now go and run around while breathing through the straw
Ooh, I like it.

I was trying to think of something for ages, eventually got stuck on filling a pond so decided it was best I just give up.
P: 15
 Quote by jarednjames Volume of a 'pipe' is irrelevant when it comes to flow rate - in so far as length goes. A longer pipe does not mean a higher flow rate. What matters here is how much the face area of the wind pipe increases with body height, not the overall volume due to length increases (in fact, length increases wouldn't help things either). Like I said previously, it doesn't matter between a certain range of heights. There will be a point where the wind pipe face area isn't enough to allow the required amount of oxygen into the lungs. As you increase a human in size, the lungs increase to the cube. But the airway surface area is a square increase. You could counter this problem by slowing breathing and taking long, deep breaths, but of course the moment you try to exert yourself and increase your rate of breathing you risk not getting enough oxygen. If you imagine a bottle being fed by a pipe, you enlarge them both as above, there will be a point where it takes: a) a significantly longer time for the pipe to fill the bottle to a useable level (in this case the required level of oxygen). b) a significantly more powerful pump to force the required level into the bottle over the same period. Even if you had a mix of both the above, it would still only help for a certain period of time. There will eventually come a point where it can't sustain you adequately.
Theoretically Agreed, but a short calculation of maximum size limit considering biological adaptation would change things beyond our assumptions of 4th grade mathematics.

For example, smallest species of whale is about 3.5 m long and the largest of them can breath with 10 times bigger size.

(I will be glad if you answer with some analytical details and do not avoid this issue just telling "because they are not same species")
 P: 3,390 Firstly, we're not allowing evolution - as per my own clarification at the start of this thread, we cannot change current human factors. Anyway, let's do some numbers. Let's assume the following: The standard human has a lung capacity of 1m3. The opening to the lung is 0.1x0.1m (0.01m2). It takes them 4 seconds to fill the lungs completely. You need all of that capacity filled in 4 seconds to survive. (I know it's not quite like that, but it will do to demonstrate the point.) Now that gives you a volumetric flow rate of 0.25m3/s and flow velocity of 25m/s. Ok, so now we double the human in size: New lung capacity = 8m3 New opening dimensions = 0.2x0.2m (0.04m2) All other conditions remain equal. Now that gives you a volumetric flow rate of 2m3/s and flow velocity of 50m/s. Ok, so now we double the human in size again: New lung capacity = 64m3 New opening dimensions = 0.4x0.4m (0.16m2) All other conditions remain equal. Now that gives you a volumetric flow rate of 16m3/s and flow velocity of 100m/s. As you can see, the rough calculation is that every time you double the size of the human, the required flow velocity to sustain them doubles also. So far, we've only taken your average height human and doubled their size twice (equivalent of going from 5.5ft to 22ft in height) and already they've gone from breathing at 55mph (which we'll take to be the 'normal' breathing flow velocity our body can withstand) to requiring a 223mph wind down their throat just to get enough oxygen in their body. All else aside, the required air speeds would tear your flesh to pieces. And that's before we get to actually generating the required pressures to attain those speeds. (Consider what it takes to artificially generate those wind speeds). Now I know my figures are way too big, but it demonstrates how vast the increases are even when simply doubling the size. Now, so far as anything that isn't human goes, please leave it out. The only answer to what you pose in your post is that they are different species, specifically evolved to those conditions. There really is no more to it. Like I said previously, we're not allowing evolution as the moment we start allowing these factors to change, anything becomes possible - and also less human.
 P: 3,390 Just something for you here: Based on rough estimates, I have a lung volume of ~0.009m3. My wind pipe is ~0.0009m2. It takes me 5 seconds to completely fill my lungs. I need ~0.0045m3 to survive with per breath. This means I have a volumetric flow rate of 0.0018m3/s and a flow velocity of 2.00m/s (4.50mph). This is the rate purely for me to survive. Now let's double my size: New lung volume = 0.072m3. My wind pipe is 0.0036m2. It still takes me 5 seconds to completely fill my lungs. I need 0.036m3 to survive with per breath. This means I have a volumetric flow rate of 0.0144m3/s and a flow velocity of 4.00m/s (9.00mph). Again, this is the rate purely for me to survive. Now you'll note again that my breathing flow velocity roughly doubles when size is doubled. So far, I've gone from 1.78m to 3.56m in height (5ft 10in to 11ft 8in). So using this as a basic formula, vn+1=2vn, and iterating a few times, gives me my required breathing rate at heights within the OP's specified range: Height = 15m, Flow Velocity = 16m/s (36mph). Height = 30m, Flow Velocity = 32m/s (72mph). I'm not typing the pressure calcs here, but according to what I've worked out, going from 1.78m to ~15m (5ft 10in to 50ft) increases the required pressure drop in the lungs (from atmospheric) by two orders of magnitude to gain the required flow velocity. Even at only 30ft in height the required pressure is increased by one order of magnitude. Of course, if the body can't supply the required pressure drop at the new 100x larger value than previously, that means I end up breathing slower. If I can't get enough oxygen into my lungs in time, I won't be around very long. NOTE: Windpipe and lung sizes are estimates, based on rough approximations from myself and figures from various sources. Both have been assumed square for simplicity. So crowbird2, is this enough "analytical detail" for you? The only final detail will be working out the maximum size a human can be enlarged to based on lung capacity. To do this, you need to know the maximum pressure differential the body can create and then apply this to the above to gain the largest human size possible. If you wish to complete the above please feel free, I however have been awake 23 hours straight, drank 2 litres of energy drink and sat a 3 hour maths paper - the only thing I'm doing right now is passing out.
P: 15
 Quote by jarednjames Just something for you here: Based on rough estimates, I have a lung volume of ~0.009m3. My wind pipe is ~0.0009m2. It takes me 5 seconds to completely fill my lungs. I need ~0.0045m3 to survive with per breath. This means I have a volumetric flow rate of 0.0018m3/s and a flow velocity of 2.00m/s (4.50mph). This is the rate purely for me to survive. Now let's double my size: New lung volume = 0.072m3. My wind pipe is 0.0036m2. It still takes me 5 seconds to completely fill my lungs. I need 0.036m3 to survive with per breath. This means I have a volumetric flow rate of 0.0144m3/s and a flow velocity of 4.00m/s (9.00mph). Again, this is the rate purely for me to survive. Now you'll note again that my breathing flow velocity roughly doubles when size is doubled. So far, I've gone from 1.78m to 3.56m in height (5ft 10in to 11ft 8in). So using this as a basic formula, vn+1=2vn, and iterating a few times, gives me my required breathing rate at heights within the OP's specified range: Height = 15m, Flow Velocity = 16m/s (36mph). Height = 30m, Flow Velocity = 32m/s (72mph). I'm not typing the pressure calcs here, but according to what I've worked out, going from 1.78m to ~15m (5ft 10in to 50ft) increases the required pressure drop in the lungs (from atmospheric) by two orders of magnitude to gain the required flow velocity. Even at only 30ft in height the required pressure is increased by one order of magnitude. Of course, if the body can't supply the required pressure drop at the new 100x larger value than previously, that means I end up breathing slower. If I can't get enough oxygen into my lungs in time, I won't be around very long. NOTE: Windpipe and lung sizes are estimates, based on rough approximations from myself and figures from various sources. Both have been assumed square for simplicity. So crowbird2, is this enough "analytical detail" for you? The only final detail will be working out the maximum size a human can be enlarged to based on lung capacity. To do this, you need to know the maximum pressure differential the body can create and then apply this to the above to gain the largest human size possible. If you wish to complete the above please feel free, I however have been awake 23 hours straight, drank 2 litres of energy drink and sat a 3 hour maths paper - the only thing I'm doing right now is passing out.
Good job, Thanks.

Now let us consider some points.

According to your view, it seems like if we plot a air speed vs time curve, it will be alternating square wave. which will surely impose kind of shock on the internal membrane of breathing tube. But in reality it is no way like square wave. Air speed will gradually increase, reach to a maximum point then fall back to zero, then alter the direction and similar thing will happen. This will not put any sudden shock on the internal membrane of breathing tube.

Also, the breathing tube is not just like a pipe, it has a complex internal architecture. Many convergence and divergence with different cross-sectional shape together will come in consideration. You will need some numerical modeling with computer aided simulation to replicate that. Different part of this breathing tube will experience different speed and pressure.

There is a term, "Boundary layer" in fluid mechanics. You have to consider that. Also the viscous-elastic behavior of air will also have to be considered for impact analysis.

The internal surface membrane and bones will also increase thickness if you think of a scaled up version of human being. Increased thickness means better re-enforcement of the internal wall of breathing tube.

Biological adaptation is a very important factor here (I think you can call it micro-evolution). Human body has a tendency to adapt changes for additional protection against regular exercise. (For example, people who use mouse for computers, a thick-skin spot is created in the wrist, if you practice folding your knees to sit on the floor regularly, there will be some thick skin spot in different parts of your leg for adapting extra load bearing capacity of the impacted area of skin). If the breathing tube got little wider to allow extra wind in the lungs, would it be impossible to sustain extra wind speed (there may be many other factors that we are not considering here).
P: 3,390
 Quote by crowbird2 According to your view, it seems like if we plot a air speed vs time curve, it will be alternating square wave. which will surely impose kind of shock on the internal membrane of breathing tube.
I don't know where you got that but I've never claimed such a thing. In fact, I've never claimed any form of shock type effects due to breathing.
 But in reality it is no way like square wave. Air speed will gradually increase, reach to a maximum point then fall back to zero, then alter the direction and similar thing will happen. This will not put any sudden shock on the internal membrane of breathing tube.
It doesn't matter how long it takes to reach its maximum speed (remember, my figures are averages - I assumed you'd realise that on reading, there will be a higher maximum value to get the required average). Stand in a high speed wind and tell me if it hurts your skin. The membranes of your body have a certain structural make up. They can only take so much. The effects of 4.5mph wind on the membrane is not the same as a 72mph wind. What I'm saying is that as the wind speed increases, the potential for it to damage those membranes also increases - if only from friction (to keep it simple).

Given that the air speed increases with the square law as per my calcs above, there is a point where your breathing air speed is high enough to damage your membranes.
 Also, the breathing tube is not just like a pipe, it has a complex internal architecture. Many convergence and divergence with different cross-sectional shape together will come in consideration. You will need some numerical modeling with computer aided simulation to replicate that. Different part of this breathing tube will experience different speed and pressure.
All highly irrelevant and unnecessary. I have shown you that in order to get enough air into my lungs, I need a certain air velocity when breathing (my average velocity - again see the note above regarding maximum values). It doesn't matter what part of the wind pipe experiences what speed / pressure specifically, the average is what matters. You can analyse it all you want, but for every value you find below the average, there must be an equivalent above to compensate for it - that's what gives you the average. So what you are saying here actually works against you in that it means that higher extremes are experienced.
 There is a term, "Boundary layer" in fluid mechanics. You have to consider that. Also the viscous-elastic behavior of air will also have to be considered for impact analysis.
I study aerospace engineering, I am very much aware of these terms. They really don't mean that much in this context, as per my above comment regarding the analysis.
 The internal surface membrane and bones will also increase thickness if you think of a scaled up version of human being. Increased thickness means better re-enforcement of the internal wall of breathing tube.
You can increase thickness all you like, but the outer layer (that is in contact with the air) will have to be strong enough to withstand the airspeed. If the outer layer isn't, it will be damaged. Remember, the strength of the outer membrane isn't increased. The factors must stay the same as per the OP. Otherwise, we could just allow evolution to increase the strength and deal with it.
 Biological adaptation is a very important factor here (I think you can call it micro-evolution). Human body has a tendency to adapt changes for additional protection against regular exercise. (For example, people who use mouse for computers, a thick-skin spot is created in the wrist, if you practice folding your knees to sit on the floor regularly, there will be some thick skin spot in different parts of your leg for adapting extra load bearing capacity of the impacted area of skin).
You're referring to a Callus? I don't know if they are the body adapting or simply an adverse reaction to extreme pressure. As far as I'm aware, it doesn't occur to aid the load bearing capacity. Can someone confirm this?
 If the breathing tube got little wider to allow extra wind in the lungs, would it be impossible to sustain extra wind speed (there may be many other factors that we are not considering here).
Well we'd need to know the physiology of the wind pipe. That would allow us to know how much it could withstand. There will be a maximum - even if it evolved to be solid steel.
 P: 3,390 I don't know why the issue of wind speed is so big here anyway. I've already outlined the major issue and that is pressure difference required to breathe. 1. You need a certain amount of air, within a certain amount of time in order to survive. That requires you meet a minimum average velocity for breathing. 2. To generate the above average velocity, you need to produce a pressure differential. As per my above calculations, the air speed increases by the square law and so you need a bigger and bigger pressure differential with each increase in height. I indicated above that you require a pressure differential two orders of magnitude larger than what I currently produce. You can't waive this away and it poses a lot of problems when it comes to the bodies "internal engineering". As an addition to my above post, an important note for you is wind chill. The faster you breathe, the greater the wind chill factor on your wind pipe / mouth. This can have severe effects on the body - heat loss rate for one.
P: 15
 Quote by jarednjames I don't know why the issue of wind speed is so big here anyway. I've already outlined the major issue and that is pressure difference required to breathe. 1. You need a certain amount of air, within a certain amount of time in order to survive. That requires you meet a minimum average velocity for breathing. 2. To generate the above average velocity, you need to produce a pressure differential. As per my above calculations, the air speed increases by the square law and so you need a bigger and bigger pressure differential with each increase in height. I indicated above that you require a pressure differential two orders of magnitude larger than what I currently produce. You can't waive this away and it poses a lot of problems when it comes to the bodies "internal engineering". As an addition to my above post, an important note for you is wind chill. The faster you breathe, the greater the wind chill factor on your wind pipe / mouth. This can have severe effects on the body - heat loss rate for one.
For a bigger human, the diaphragm muscle (Thoracic diaphragm, by which we pump our lungs) will also be bigger and stronger, it will not be a problem creating the pressure differential.

You need detail computer aided analysis (considering possible biological adaptations) for determining maximum possible lungs size. Just some high school math is not enough to decide about this type of issues.

 Related Discussions General Discussion 112 Biology 5 General Discussion 44