So because I’m a nerd and it’s also useful to debunk crazy conspiracy theorists who think the Great Pyramids were built by giants or something, I’ve been looking into the square cube law and specifically how it affects biology and evolution, why it’s impossible for there to just be bigger versions of smaller animals, past a certain point. I understand the basic principle, height is determined by length (x), strength is determined by the cross section of bone and muscle (x^2,) and weight is determined by volume (x^3.)
So sadly, no giant humans or dragons. But here’s the thing I don’t understand: evolution (probably) doesn’t work by just coding in “human x2,” it’s complex and occurs extremely gradually. So, if there was for some reason an evolutionary pressure that suddenly made it REALLY beneficial to be way bigger, wouldn’t it be possible for an organism to slowly evolve to be both larger and also have thicker joints and bones and more muscle mass, as well as all the other adaptations, to cope with that?
I mean, isn’t that basically what giraffes did, at least as far as their necks go? Is there something I’m not understanding here? Is it possible, just very improbable since there’s very few scenarios in which it’s both beneficial and practical, since all the issues involving energy and heat, for something to be that big? Please enlighten me!
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The thing is, it’s also in large part about the overall structure of the organism. Humans are about as big as they can safely be with our structure – bipedal, 4 limbs, a curved lumbar spine, etc.
Larger animals have almost always been 4-legged, as the square-cube law is going to make the support of the weight much easier. Just look at the joint/back problems the largest humans invariably get – supporting that much weight on 2 ankles is rough. Especially ankles and that are super flexible like ours, made up of a lot of bones. Elephants get away with it by having much simplified ankles and feet – they can’t wiggle their toes or turn their ankles much.
Our lumbar spine is also about at capacity – we already suffer from back problems all the time because of the extra weight on a curve that was never meant to be upright. Not to mention other things like our lung capacity – relative surface area of our lungs for gas exchange is going to reduce also because of the square-cube law, larger mammals have to have larger torsos to accommodate larger lungs.
So yeah, we could theoretically evolve 2x larger humans if there was pressure for it, but a 15 foot tall man would really stop looking very human – they would probably adapt their posture to slouch much more, be really barrel chested like a gorilla, lose a lot of dexterity in the feet as some of the bones fused to support their weight, etc. They would be much less agile than current humans, as the price we pay for agility and skeletal articulation is an inability to support much more size.
If survival necessitated it, then you would only see the survivors anyway.
> So, if there was for some reason an evolutionary pressure that suddenly made it REALLY beneficial to be way bigger, wouldn’t it be possible for an organism to slowly evolve to be both larger and also have thicker joints and bones and more muscle mass, as well as all the other adaptations, to cope with that?
Sure. That’s how the dinosaurs worked, although rather simply than evolving to be super ripped and muscley after working out at the dino-gym, they also evolved to be super light for their size, with hollow bones and everything. Back then, there was more food to sustain them, so larger herbivores could defend themselves better, and getting bigger meant predators could subdue them better. It’s also how giant sea creatures like whales work.
There are other concerns about evolutionary pressures like that – will another species beat you to that niche and outcompete you? Is the pressure so strong that it kills your species before they can adapt? Will you even adapt in the first place? Natural selection is just throwing darts at the wall and seeing what sticks, and sometimes you don’t hit what you need.
There arent many bipedal creatures much larger than us.
For us to be scaled 2x. weighing 800kg… thatd be rough. We probably woudlnt want to be walking upright when so heavy. That poor spine would suffer under that mass.
More likely we would adapt some gorilla like walk. Hunching and using arms alot for support.
Evolution is not that complex, and doesn’t even occur necessarily gradually. It’s shortcut for “random gene mutations which survive and become more prevalent across generations”. And “occur” means “how many individuals carry that mutation in the next generation”. Also, “immediately” means “in one generation” and “quickly” means “in a few generations” – which in calendar years depends obviously on the length of a generation, i.e. how much times goes in average between birth and reproduction.
So “beneficial” is only about a random mutation giving the carrier a better probability at reproduction overall. It’s not about the individual per se.
Say that a mutation occurs which makes carriers much stronger than average but almost always infertile. This mutation would be very likely beneficial for the carriers’ survival, but catastrophic for their reproduction: so it will disappear quickly. It’s not “beneficial” evolutionary, even if it plainly it is for the carrier as an individual.
A giraffe which got a “longer neck” random mutation would have had all considered a reproductive advantage with respect to giraffes without it.
All considered involves the environment where the giraffe lives, but also the thermodynamics of the individual and of course other random mutations that may be present in the same individual(s).
It’s just the total probability of reproducing that matters.
Arguably, the probability of survival of the offspring is also critical, but that’s just another type of all considered, and for example human brain is exactly skewing that specific bit of all considered enormously: by allowing us to create social structures, we both greatly increased the chances of survival to reproduction and the survival of the offspring.
So about size: can certainly happen. For example certain dinosaurs were apparently very big. Obviously they evolved because being very big gave them some reproductive advantage in their environment.
For humans, if the environment changed (gradually enough not to cause extinction) so that food was available only to taller individuals, you would see the height and size of individual increase, if that overall increased the chances of reproduction (for example, accompanied by another random mutation that reduces the minimum age of reproduction).
The square-cube law doesn’t mean no giants at all.
It just means you can’t take a plan meant for something small and scale it up without changing anything else.
If you scale up an object to be twice as tall and keep everything else the same, it will have 4 times the surface are and 8 time the volume.
If you keep the density the same, 8 times the volume means 8 times the mass and weigh.
So if you were twice your size and not have any of your proportions changed you would weigh 8 times what you do now.
The bones in your legs would weigh 8 times as much and would need to hold up 8 times the weight.
However the strength of your bones is determined by the cross section. A bone twice the size in every dimension would only have 4 times the cross section are.
So if you simply scale up the design you would have a problem.
If you scaled up a human to 10 times their size ala attack of the 50 foot woman. The giant person would weigh 1000 times of what a 5 foot person would weigh with bones that could carry 100 time the weight.
A giant that tall would break their bones trying to stand on their own legs.
And it is not just bone strength.
Everything in the design of the human body is optimized for our normal size and going to far beyond the range it is designed for will cause issues.
The surface are of your skin only grows with the square of your size, this will cause problems with heat dissipation.
Your heart will need to pump blood though your body which can lead to all sorts of problems is you need to pump blood up from the ground to several stories high.
All sorts of body functions won’t work at different scales.
There is a reason while toddlers can fall on their face and be fine, but adults can die from similar fall. Also animals like horses have necks so long that throwing up is not really a thing they can do.
Small animals basically can fall from any height and be fine, while large animals can’t.
It is not just humans and animals.
All sorts of living things and natural and man made structures are designed either by natural selection or by humans to be optimized in the way they are build for the size they are.
You can’t scale up ow down most machines, buildings, structures, animals or plants and expect them to still work.
This however doesn’t mean that you can’t have very big or very small things.
Elephants exist. They are big. Elephants are closely related to hyraxes. Hyraxes are very small and elephants are very big and evolution had no issue in creating both from a common ancestor.
The issue is that evolution did just scale up and down the same body plan, but instead optimized everything for the new size.
Elephants have very thick leg bones. Hyraxes are furry.
You couldn’t scale up a human to giant size and expect the body to still function, but that doesn’t mean that evolution could not adapt a human body plan to work at larger sizes.
The proportions would need to change and lost of other anatomy would need to be different and the taller you made the giant the less they would look like a human.
In fact we think that there was a primate (a close relative of us humans) alive not too long ago who was much large than any human or other ape alive today.
Gigantopithecus was like some sort of Orangutan relative that walked the earth right up until the first anatomically modern humans appeared on the scene. We don’t know how large that ape could have been because we only have found a few bones and a number of teeth, but twice as tall as a human seems likely.
Not a giant or King Kong, but much bigger than you could scale a human body and keep the human healthy.
Humans that grow super tall tend to be really thin and have all sorts of health problems and tend to die young.
If there was enough evolutionary pressure to do so, evolution could scale up primates quite a bit. If there was enough food and a good reason why growing that tall would make you more likely to pass on your genes, evolution would find a way.
The largest land mammal ever was Paraceratherium, an extinct rhinoceros relative that was more than 15 feet tall at the shoulder.
The whole two legged gait might seem like it could be a problem, but T-Rex walked on two legs too.
So giant humans relatives are not prohibited by evolution, Evolution just never had a reason to make any and if it did they would not look like scales up humans.
a bit of a sidestep here, but if i recall correct, what’s happening is chance: there’s a chance you’re bigger than your parents, which has a chance of you getting more offspring, which has a higher chance to also be bigger/taller.
Now that’s only one part of the equation. Remember giant insects? that was during the Carboniferous period, or close 300 million years a go. Why could they exist then, and not now? oxygen levels. Apperently the oxygen level was around 35% back then. So when the oxygen levels dropped, the big insects did not have enough energy to move, or survive. Getting smaller gave them a better chance of survival, more offspring, etc. and there we go.
Evolution is purely chance, and the result of that chance. IF your genetic differences aren’t advantageous for procreation, your differences will be outbred.
If f.i. someone has a genetic difference which would make him/her larger, and it has no advantage, chances are, it will die out. We see this all the time: Klinefelter syndrom, xyy syndrom are just examples of genetic differences which make people larger. however, there is no real advantage here.
For humans you can even consider the opposite is true : we tend to compensate for genetic differences. People with bad or no eyesight, hearing or limited fertility. We find solutions so they can be an active member of society instead of just leaving them to die as inferior babies, which a lot of animals do. Keep in mind, i’m not mentioning this to offend some sensitive person, but it is how life in nature goes. If a lion cub is born with 3 legs, or a blind horse, it will be abandoned and die, or it won’t be able to keep up, and die that way.
It is however a sensitive subject, because before you know it, you’re going in to directions which can spiral out of control. Think f.i. to gene therapy, or selective breeding. While we do this all the time with plants and animals, this is a taboo subject when it comes to humans, and imo it should stay that way. We’ve done this f.i. with bananas, and we’re pretty close to losing them since only one cloned version of bananas still exist, and it’s very vulnerable to a fungus. Since other versions are all gone, there is little diversity and we can not crossbreed it in to a better resistant version.
Large animals exist and all large animals were at some point a smaller animal. I think it’s obvious the answer is yes, of course with evolutionary pressures animals will adapt to be larger. Otherwise why would whales or dinosaurs or even elephants exist? Even insects used to be giant back in the day. The square cube law doesn’t prevent animals from getting large, it just prevents you from magically scaling up an animal and expecting it to function.
Op you might like the “your dinosaurs are wrong” episode about sauropods. Fascinated me since they’d have structural air sacs to help hold their head up without insane bone mass
The square cube law doesnt dictate that animals cant exceed a certain size. It just means that if you magically scaled up an animal 10x its current size, it would not be able to stand, move, or support itself.
Theoretically there should be no real limit on how big an animal can get. Just look at the massive sauropod dinosaurs. But the challenges you would have to get are basically 1. Being able to pump blood around your massive body, 2. Have a strong enough skeletal structure to support all your massive muscles and organs, 3. But still be light enough to move around in a meaningful way otherwise you cant eat or mate, 4. Have enough food around the sustain your size. Oh and yes have some kind of selection pressure that actually leads to larger and larger offspring as a sustainable trend. Its incredibly unlikely to occur but theres no reason why these perfect storm of conditions couldnt come together to create a super megafauna like the sauropod.