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388 years ago, Galileo worked out why human giants can't exist

scientificamerican.com

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Re: 388 years ago, Galileo worked out why human giants can't exist

#21

Post by dahart »

> for if his height be increased inordinately he will fall and be crushed under his own weight

> scaled-up wooden houses would not support their own roofs

Hmmm this argument fails to mention giraffes, elephants or dinosaurs. (Edit: ooops it does mention elephants and dinosaurs) But clearly, land animals with bones can be quite a bit larger than humans. Similarly the houses comment ignores that large multi-story wooden buildings that support their own roofs exist, and already existed in Galileo’s time.

There might be reasons today’s evolution of human anatomy can’t get any larger than 9 feet tall, but this argument about physics and bones and square vs cube growth rates is pretty unconvincing. The argument skips right past the idea of “giants” that are only 1.5x or 2x or 3x taller, rather than 10x or 100x taller. Sure animals cannot be “inordinately” bigger, but that does not explain why they can’t be twice as big.

Re: 388 years ago, Galileo worked out why human giants can't exist

#22

Post by adrian_b »

stevenwoo wrote: post #12
vivekd wrote: post #4

I don't know how convinced I am. First there were dinosaurs in the past, the brachiosaurus was 4 x as big as an elephant and there are probably yet undiscovered dinosaurs that were even bigger given discovery of partial fossils like the Sauroposeidon. Also we know in the past there were dargonflys with wingspans greater than 2 feet and centipedes that grew as long as a car.

They were larger but not as dense as mammals, we know had adaptations like less denser bones and different respiratory systems that allow for more efficiency and much more rapid growth into maturity. Modern birds show evidence of all these traits. When the Chicxulub extinction event happened it reset things so mammals got the upper hand on large sizes and eventully won out for the most part. Highly recommend The Rise…

You are right that they had pneumatic bones and air sacs and they were not as heavy as mammals with the same volume would have been.

Nonetheless, the biggest dinosaurs were several times heavier than the heaviest terrestrial mammals that have ever lived, which in turn were several times heavier than the biggest elephants of today.

So probably dinosaurs were close to the size limit that is imposed by the mechanical properties of vertebrate tissues like bones, tendons and muscles, while in the present terrestrial mammals the size is limited by the availability of food and by the humans who have always hunted preferentially the biggest animals they encountered, and not by the strength of their bones.

Re: 388 years ago, Galileo worked out why human giants can't exist

#23

Post by CM30 »

TV Tropes calls it the Square-Cube Law, and cites Galileo in the real life examples section:

https://tvtropes.org/pmwiki/pmwiki.php/Main/SquareCubeLaw

It's the reason why giant robots probably couldn't be as agile or powerful as in something like Transformers or Gundam, and why kaiju like King Kong or Godzilla couldn't exist in the real world.

Re: 388 years ago, Galileo worked out why human giants can't exist

#26

Post by Melatonic »

timedude wrote: post #19

Important to keep in mind that the earth was smaller back then with lower gravity. The earth grows like all other living organisms.

So does the moon though so it all evens out. Bigger gravity of earth pulls you down and bigger moon stretches you out.

Hopefully no cheese eating space mold gets up there or we're done !

Re: 388 years ago, Galileo worked out why human giants can't exist

#27

Post by r3trohack3r »

dahart wrote: post #21

> for if his height be increased inordinately he will fall and be crushed under his own weight > scaled-up wooden houses would not support their own roofs Hmmm this argument fails to mention giraffes, elephants or dinosaurs. (Edit: ooops it does mention elephants and dinosaurs) But clearly, land animals with bones can be quite a bit larger than humans. Similarly the houses comment ignores that large multi-story woode…

> dinosaurs

True for Scientific American today, not true for Galileo.

“Dinosaur” wasn’t a thing we started knowing about until the early 1800s. Benjamin Franklin died not knowing Dinosaurs were a thing.

But Galileo would have certainly known about elephants though.

Re: 388 years ago, Galileo worked out why human giants can't exist

#28

Post by Retric »

dahart wrote: post #21

> for if his height be increased inordinately he will fall and be crushed under his own weight > scaled-up wooden houses would not support their own roofs Hmmm this argument fails to mention giraffes, elephants or dinosaurs. (Edit: ooops it does mention elephants and dinosaurs) But clearly, land animals with bones can be quite a bit larger than humans. Similarly the houses comment ignores that large multi-story woode…

Yea, we’ve scaled wooden buildings to 25 stories.

Arguments around bone scaling ignores the impact forces of running. Scaling often means trading margins not just keeping all constraints the same.

Re: 388 years ago, Galileo worked out why human giants can't exist

#29

Post by dahart »

r3trohack3r wrote: post #27
dahart wrote: post #21

> for if his height be increased inordinately he will fall and be crushed under his own weight > scaled-up wooden houses would not support their own roofs Hmmm this argument fails to mention giraffes, elephants or dinosaurs. (Edit: ooops it does mention elephants and dinosaurs) But clearly, land animals with bones can be quite a bit larger than humans. Similarly the houses comment ignores that large multi-story woode…

> dinosaurs True for Scientific American today, not true for Galileo. “Dinosaur” wasn’t a thing we started knowing about until the early 1800s. Benjamin Franklin died not knowing Dinosaurs were a thing. But Galileo would have certainly known about elephants though.

> True for Scientific American today

Right, that’s what I was implying. However, I looked again and the article does mention elephants and dinosaurs.

Re: 388 years ago, Galileo worked out why human giants can't exist

#30

Post by ndr »

necovek wrote: post #16
ndr wrote: post #7

Earlier quoted context omitted.

1. They stand on 4 limbs, rather than 2. 2. That would be assuming that human legs are sized at the max capacity they can carry, which is not true.

Regarding 1, horses in particular are known to jump off two hind legs and land on their two forelegs, putting a lot more force on them than their stationary weight. On 2, I believe that's the GP's point too — human leg bones (or horses') can obviously take a lot more than their standing/walking/running weight.

Agree re 1, but point 2 still stands.

They can take more stress than standing, but the scaling law is still there.

If you scale linearly height/section the max stress won't scale linearly because the weight will scale cubically.

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