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Question

How small could a human scale down to?

Requirements

Must be able to work stone, metal, and wood.

Notes

-If we can assume they evolved in a place with temperatures where they wouldn't freeze or cook to death, and figured out how to make clothes/fire to keep them warm so they could expand out into new areas.

-There are primates out there that are only ~5" tall. Along with a lot of mammals born hairless/nearly hairless of extremely small sizes and adult sizes.

-As I noted above, the smallest human I've found was less than 2' tall without mental disabilities, only minor physical disfigurements, capable of weaving garments for a living, walking unassisted, and died at 75 years old in a remote village of third world country.

-Humans wouldn't be dwarfed by everything in this scenario. I would also selectively scale down the flora and fauna of the world to give them similar conditions to what we have in the real world.

-Resources would obviously be much more plentiful

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  • $\begingroup$ I still find panda weird how can the cub smaller than a fist grow into a big furry baby standing 1.8m (assisted)? Skipping the adult stage entirely and still doing fine in the wild and behind bars maybe your homo parvis(small) can learn a thing or two ;D $\endgroup$
    – user6760
    Jan 31 '21 at 8:08
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    $\begingroup$ Scaling down has limits. 1) temperature control, smaller has more surface per mass thus cools to quickly. 2) neurons & cells cannot shrink, so if you reduce brain size you sacrifice neuron count. How small can a brain be and still be fully human? $\endgroup$
    – PcMan
    Jan 31 '21 at 9:53
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    $\begingroup$ For questions on what changes with scaling people up or down, I highly recommend the "The size of life" series on Youtube by Kurzgesagt - In a Nutshell. $\endgroup$
    – Mookuh
    Jan 31 '21 at 12:29
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The square-cube law works in both directions, scaling up and scaling down.

When you scale up you hit the wall of the mass (it grows with the volume) to be supported by the bones (it grows with the area), so at a certain moment your upscaled being would collapse under its own weight.

When you scale down the area through which you waste heat to the outside grows more than the volume producing the heat, so you reach a point where your internal engine is throttling at full speed just to stay idle.

I think the size of a newborn is the smallest a human body and metabolism can handle with no big issue. I mean, newborns need to be covered and protected, but I suspect mostly because their thermo-regulation mechanism is still not well tuned. When we were still roaming in the open we didn't have caps, suits and blankets but we managed to survive birth.

However mind that if the adult is the size of a baby, you need to handwave how their baby can survive, considering that they would be born way smaller.

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    $\begingroup$ Excellent answer. Possibly worth nothing that the effects of scaling down can be empirically observed in nature. Almost all mammals that are significantly smaller than an adult human have both a higher core body temperature and a higher resting heart rate, and both tend to go up as the size of the animal goes down. $\endgroup$ Jan 31 '21 at 16:05
  • $\begingroup$ Fur or feather solves the heat-loss issue. Hairy people, sounds fine to me. $\endgroup$ Feb 1 '21 at 4:02
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Fully functional with no problems:

You CAN have people be pretty small. People with disorders and health conditions are, unfortunately, the folks most represented by the very short.

But there is a fully functional population of extremely short people, who's size appeared to have no adverse effects on them - their size was normal for them. Homo floresiensis was only about 1.1 meters tall (quite short) but appeared to have comparable technology to the modern humans of their time.

Small humans can, through tool use, perform almost any function of larger humans. In a warm climate, heat loss should be relatively minor as an inconvenience (these folks lived in the tropics).

It is entirely possible to get to smaller sizes if these folks could reach this small stature. But they are the smallest fully stable population to have an entire society based around them. I'd stick with "hobbit" people as your standard.

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You don't need to scale down too much. A 2m Man has a big advantage over a man with 1m80 when fighting. Take swords or fists, it doesn't matter. The bigger man has a longer reach with his fist. He can also use a longer sword than the smaller man, which emphasises the size advantage further.

So if you scale down your humans, you don't need to be too extreme. It would totally work if your humans have 1m20 and your giants have 2m10. Throw in the New Zealand eagle, which had a wing span of up to 3 meters, and you have all you need for a fantasy world.

1m20 is like a child with 6 or 7 years. Just as you can easily lift that kid, or win against it when it decides to "attack" you, those giants would have a tremendous advantage in real fights.

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No need to go into prehistory or fancy genetic modifications - the Pygmies is/are a group of people wih the average height about 150cm, living in or around Congo. Throw in 2.2m perfectly functioning basketball players (or elite warriors) and you have the settings.

See this photo (from 1890, courtesy of Wikimedia): enter image description here

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    $\begingroup$ "Pygmies" is a term from Greek mythology, but races of short stature such as the Batwa are quite alive and well today. For all humans met to be short, an RPG could be set in the past (the island Flores, where 4-foot people fought 18-foot Komodo dragons, and cooked them for dinner), or in the future, where such humans would be expected to have a small but steady advantage in interstellar colonization. $\endgroup$ Jan 31 '21 at 22:58

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