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Q & A: King Kong vs. Galileo: are bigger animals possible?

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Most recent answer: 03/09/2011
Q:
Do Laws of Physics clearly pose limitations to the size of living organisms? Long time ago I read somewhere that a giant Gorilla, like a King-Kong, is something that can not exist mainly because of its weight. The article went on to explain with more detail about the Physics and the Mechanics that are involved. It talked mostly about the role of the Gravitational force here on Earth. I don’t remember much unfortunately but the emphasis I think was in Physics rather than Biology. Actually I really need to know if it is impossible for a huge and obviously really heavy animal to exist on Earth’s environment and conditions. I don't care about the evolution process, it’s the physics that I am interested. An elephant today can reach 10 tons but there were Sauropod dinosaurs 17 meters tall that weighted 73 to 122 tones and there are speculations about one reaching more than 200 tones. And these guys were around for millions of years. Walking in all fours off course it’s easier to support the weight. Let’s hypothesize that indeed there were perfect conditions in the past on Earth for such a huge animal to exist. In general everything to have been just right for such an animal to develop. And for the sake of the argument no Evolution trait for economizing on energy and other similar “guidelines”. Let’s take for granted that Nature gave the green light to go ahead with this. I am talking about a gigantic creature more than 100 meters tall (Gorilla shape). Would it be possible then for such a huge animal to exist? I mean regardless of birth and development, as an adult animal would it be able to move around normally? Would his muscles be enough to lift his arm? Would his limbs function normally? Does the length of the limbs play any role? I am talking about Physics here. Let’s assume that Biologically it is possible and that it wouldn’t have issues with internal organs and other details. Do you think that its own weight would be the main problem? And the bone structure, necessary to carry (without breaking) the rest of his muscle tissues and organs, would that have to be enormous, adding more weight to the whole? Is it all a matter of the Square-cube Law and the cross sections of the bones as presented in J.B.S. Haldane essay “On Being the Right Size”? (The Question is not very different than asking about a really huge man made airplane. If we could build a 4 miles long airplane with some super light and super strong materials and very long wings off course and some powerful engines would it fly? Strength of materials aside in the case of an airplane we need to care about its weight and aerodynamics only right? So if the weight is right, then size doesn’t matter. Or is there a limit posed by characteristics of Air /atmosphere and friction? I don’t know about that.) If this is the case, the problem caused by the strength of the bones actually, could we go a step further and say that IF and only IF its bones were made of another material, a super light but super strong material (like carbon fiber and better) then it might be able to walk and move normally without problems? Is the weight the only issue here or am I missing something else? So, my question is this, aside of biological factors, would a huge animal be so heavy that it couldn’t function and if yes then what if its weight was kept below a figure somehow, is there any other Law in Physics that would make it impossible for such a huge organism to move and function without problems? It is really important to me to understand this thing so please take your time and give me an answer when possible. Thank you very much for your work so far.
- Tony (age 23)
Greece
A:
You've put your finger on the key point- that the cross-sections of limbs scale as the square of the lengths but the weights scale as the cubes. As a result, if you just try scaling things up too much, the weights are too big for the limbs to support. Of course if you could replace the bone with something stronger, you could buy a little room for further growth, but the basic scaling constraints still hold.  Notice that if the earth were smaller, then it could support larger animals, since gravity would be weaker.

I hadn't known about Haldane's essay. Presumably he did not claim credit for the idea. It was set out clearly by Galileo in Dialogue on Two New Sciences.

Mike W.

(published on 03/09/2011)

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