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I'm currently working on an alien humanoid race that lives on a planet with twice the gravity of earth. Despite this however, the humanoids are about the same size as an average human if not slightly taller. They also possess great strength and speed. Is this possible? How could a bipedal creature endure the pressures of gravity? Would their bones and muscles be stronger? What about things like their diet? All in all, how would they look like, if their possible at all?

Edit: Also, what about their blood pressure?

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  • $\begingroup$ Why do you need twice the gravity? Anyhow, biochemistry developed more or less by chance over billions of iterations and is highly complex. You can always say they just are. Nobody knows what small changes to you on a chemical level would really do. They might use slightly more effective molecules and be exactly like we are as a result. Nobody can prove you wrong as long as you don't overdo it and leave it at small changes (twice the gravity is small enough, you can't prove me wrong, that's my point). Please don't try to argue with our biology on alien worlds, that's just unrealistic $\endgroup$ – Raditz_35 Oct 14 at 8:03
  • $\begingroup$ It's fantasy; you want it, you make it. The question is rather how to bent reality in your favour. How could these features be explained despite their contradictory circumstances. $\endgroup$ – Backup Plan Oct 14 at 8:14
  • $\begingroup$ We have animals on Earth which are much taller than us; and some of them also both taller and much heavier. And that's in the present; in the past there were bipedal animals very much taller and very much heavier than humans. So it is obviously possible. $\endgroup$ – AlexP Oct 14 at 10:49
  • $\begingroup$ @Johnara I don't know why you want or need the planet to have a (surface?) gravity twice that of Earth. Do humans visit the planet and spend much time there? As I remember centrifuge tests indicate that spending as little as a week in significantly higher gravity is bad for human health. If you don't have human characters visiting your planet and comment on how much heavier they feel, how will the readers know that the planet has twice the gravity of Earth? The gravity will seem normal to the natives. $\endgroup$ – M. A. Golding Oct 14 at 17:15
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Yes: Consider terrestrial creatures with significantly more mass than humans as an example.

This creates a situation functionally similar to a 'normal-ish' human on a super-earth. A body with enormous mass and internal pressure. For example, look at the physiology of a giraffe. In order to contain the massive blood pressure in their bodies, their skin must be incredibly thick and tight, growing thicker and tighter the closer to their feet/hooves you get, because the pressure the further down you go increases non-linearly. This is the same reason water towers progressively get more rings the closer to the base of the container you get. enter image description here

The other thing a giraffe needs is extremely thick arteries and veins, as well as a huge heart to deal with having to pump all that blood at high pressure around the body. Plus huge thick bones capable of taking the strain that, like the skin, get tougher the lower you go on the animal.

If you give these humanoids features roughly similar to this, it should be possible for them to exist. Interestingly, these similar properties would be needed for giants to exist on earth.

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