Human development in different gravity

I'm writing sci-fi novel now, and it mainly revolves around 2 planets in the same solar system.
Humans arrive there on the arkships from earth, but the ships are built as a one-way vessels, and it takes both planets thousands of years to enter space age again and finally be able to meet.
So there's no contact between them.

A question I have is how would humans look if the gravity on the planet B was 10-20% higher than on the planet A? Would they be taller and with thicker bones, more developed musculature?
My idea is not so much about evolution as natural selection.

What do you think? Am I off the mark? How would height change over, say, 3000 years on two planets with different G?
Or will they stay largely the same?

I think I will go with higher & more muscular humans anyway, even if it's not scientific to expect the difference to occur in such a short time. But I still want to know what yall think.

Height depends on more factors than just gravity, but all other things being equal I would expect heavy-worlders to be shorter rather than taller. That, however, is just an intuitively reasonable-sounding bit of SF convention and all other things are rarely equal, so I would say do what you feel. There are some interesting answers to this question, or one like, on StackExchange here.

That said, what other factors can affect average human height over thousands of years to be higher? I don't mind scratching out gravity altogether, I just want this one race to look taller and bulkier on average.

I think the major long-term factor is availability of nutrients, especially protein. Populations with better access to quality proteins will grow taller on the whole than those without. Muscle mass is a question of lifestyle. So I would say if you want them tall and bulky, giving them an extremely high-protein diet and a strenuous cultural occupation combined with the high gravity would just about do it.

To build off of what Cyranoj said. Perhaps you could have it so that the people that are taller and bulkier had a harder time with the colonization. Their arkship crashed and left them with a bare minimum to work with? That would require them to put in much more physical labor along with hunting and foraging for a different diet. The other colony had no issues and have led lives of near luxury in comparison.

Perhaps you could have it so that the people that are taller and bulkier had a harder time with the colonization.

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That's exactly the case. Basically, the first planet has a rather mild climate and not very challenging nature. It's basically very similar to earth in this respect.

The second planet is closer to the sun and hotter (so much so that the equator couldn't be easily populated without special buildings and machines to cool everyone off. This planet is mostly jungle, savannah and deserts, with no winters to talk about (but rain seasons instead).
The fauna is very large and aggressive, so yeah - they've had a rough time colonizing it.

Do you think it's plausible to make them muscular and taller as a race just based on the challenging environment and nature? They aren't supposed to be very tall, but described as a head taller than the people of the first planet, on average, and with wide shoulders and strong frame. But not like gorillas and Hulks. Just your average image of a college soccer team captain

I kind of agree with CyranoJ except I keep thinking of the elephant? Would it still be the same size in a lighter gravity or even a heavier gravity?

I also think about how much taller modern humans are than just a century ago.

My theory is that heavy gravity would produce a large, thicker humanoid. Much like the mastodons or dinosaurs of long ago. Supposedly, the large dinosaurs live in a time when the earths gravity was less or the poles were changing or something like that.

A lighter gravity would produce a taller, thinner humanoid. Kind of like a stork or flamingo today.

Most sci-fi writers I have read in the past, Heinlein, Reynolds, etc., have used these two in their character development. I have read nothing to contradict this.

Hope this helps.

3000 years wouldn't be enough for substantial evolution to take place, but there might be some evolution if the environment was really severe, creating intense natural selection pressure.

Diet would be the biggest factor, in two ways. Evolution aside, the group with access to better nutrition would be taller. Another factor would be what they have to eat. A hunter gatherer society would evolve differently from a plant cultivation society -- more emphasis on being able to run.

Basically not much is actually known about how high gravity would affect people's development. The short-and-stocky-heavyworlder trope common in SF is just loose, marginally-informed guesswork.

It might be more worthwhile to think about what will feel poetically true to your audience. In this sense, the tropical hot planet may well feel less likely to produce the kind of specimens you require because tropical Earth environments tend to be sparse and difficult nutrient-wise. Though even so such enviornments did produce the Maasai, or could produce a taller noble cast among otherwise nutrient-starved peasants.

"Earth-like" environments of course could mean many different things. An "Earth-like" environment in a heavily-glaciated context could mean something like prehistoric Earth, which was favourable to megafauna (and that could include your large humans, again poetically rather than scientifically-speaking).

That said, maybe the tropical planet has protein sources that wouldn't exist on Earth, that your football captains subsist on. You have a lot of freedom of movement here, is my point. If you want to put some quasi-scientific work into justifying your decision, you can probably find a rationale for anything you choose with a little effort.

Nezhul said:

A question I have is how would humans look if the gravity on the planet B was 10-20% higher than on the planet A? Would they be taller and with thicker bones, more developed musculature?
What do you think? Am I off the mark? How would height change over, say, 3000 years on two planets with different G?
Or will they stay largely the same?
I think I will go with higher & more muscular humans anyway, even if it's not scientific to expect the difference to occur in such a short time. But I still want to know what yall think.

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Assuming a bi-pedal, upright animal, I think that those on the stronger gravity planet would be short & stockier. But not by much.
3000 years isn't a lot in anthropology.

Nezhul said:

I'm writing sci-fi novel now, and it mainly revolves around 2 planets in the same solar system.
Humans arrive there on the arkships from earth, but the ships are built as a one-way vessels, and it takes both planets thousands of years to enter space age again and finally be able to meet.
So there's no contact between them.

A question I have is how would humans look if the gravity on the planet B was 10-20% higher than on the planet A? Would they be taller and with thicker bones, more developed musculature?
My idea is not so much about evolution as natural selection.

What do you think? Am I off the mark? How would height change over, say, 3000 years on two planets with different G?
Or will they stay largely the same?

I think I will go with higher & more muscular humans anyway, even if it's not scientific to expect the difference to occur in such a short time. But I still want to know what yall think.

Click to expand...

You mentioned natural selection. Keep in mind that if the species is advanced then natural selection is not going to be a substantial issue in evolution, because the species will have sufficient medical know how to maintain a low death rate. It's not likely that some individuals will be more likely than others to die because of gravity, so gravity likely won't affect evolution, except over a very long time -- maybe.

What's likely to create natural selection pressure on one planet over another is things like food scarcity, dangerous predators, and/or disease. If you can think of a way that higher gravity actually kills people, then it would create selective pressure and cause evolution.

The other possibility is that the species has sufficient know how to guide or cause its own evolution and adapts itself to the gravity via artificial means.

Nezhul said:

I'm writing sci-fi novel now, and it mainly revolves around 2 planets in the same solar system.
Humans arrive there on the arkships from earth, but the ships are built as a one-way vessels, and it takes both planets thousands of years to enter space age again and finally be able to meet.
So there's no contact between them.

A question I have is how would humans look if the gravity on the planet B was 10-20% higher than on the planet A? Would they be taller and with thicker bones, more developed musculature?
My idea is not so much about evolution as natural selection.

What do you think? Am I off the mark? How would height change over, say, 3000 years on two planets with different G?
Or will they stay largely the same?

I think I will go with higher & more muscular humans anyway, even if it's not scientific to expect the difference to occur in such a short time. But I still want to know what yall think.

Click to expand...

Natural selection is the major mechanism of evolution, so to say your "idea is not so much about evolution as natural selection" indicates you don't really understand either. Not to worry; you're in the same boat as most people.

I won't try to give you a whole course in evolution, but I will try for a brief (simplified) bit before addressing your question. Evolution is, simply enough, changes in the genetic structure of populations. Changes in individuals represent environmental effects on development or acclimatization; these are not transmitted to the offspring, and aren't part of evolution. Natural selection is, also simply speaking, differential reproduction. If an inherited characteristic results in its possessors leaving more, fertile, offspring than those without the trait, its frequency in the gene pool will change. Natural selection is the major factor in evolution. Mutation is the next significant factor, and it is heritable changes in genes. This is the source of new variation in populations. The next mechanisms are the "population effects," including genetic drift - random variation from one generation to the next, mostly of significance in small populations, population admixture - when two populations with different gene pools merge, and founder's effect - where a smaller population, with only a portion of the parent populations gene pool, splits from a larger one to start a new population.

Founder effect and genetic drift would give the major foundation for your situation, with natural selection left to act on the resultant gene pool. 3000 years is about 120 human generations, not much time for natural selection, but it is possible, particularly if the was some factor in the selection of the space travelers that would provide a basis for rapid change. If, for example, the travelers had been selected for height and strength, the genetic components of this would provide a narrower base (founder effect) for more rapid evolution.

Unfortunately, however, height and strength are highly plastic human characteristics: genes set upper and lower limits, but environment plays a major role. For example, genetic twins reared apart are known to differ by as much as 30 cm (1 foot) in stature as a result of nutrition, living space, and many other factors. In general, though, tall people with a lot of surface area through which heat is lost tend to be found in hot areas (the Masai, for example), while short, stocky is favoured in colder climes (for example, the Inuit). But this is only a trend, not a guarantee.

Gravity does, however, have a significant effect on individuals' skeletal tissue. In low gravity, such as on the MIR space station, bone mass is lost; that is why NASA runs so many studies of exercise in space. Your space travelers would need some sort of a "gravity mimicker" to avoid arriving at the new planets with any bone at all; 6 months at the space station means 12% of bone mass lost.

It is possible (we don't have any studies - they're not possible) that increased gravity would result in greater bone mass and density since bone is laid down more densely where there is stress (that's how we can tell your activities from your skeleton - using different muscles places particular stress on the bones to which they are attached, and more skeletal tissue is laid down to support the stress).

So my best suggestion for your story is to have your travelers selected for the characteristics you're looking for and then have them land in an environment that favours those characteristics, remembering that the characteristics are as much environmental (nutrition, exercise, etc) as they are genetic.

Good luck with your story.

SimonDoom said:

You mentioned natural selection. Keep in mind that if the species is advanced then natural selection is not going to be a substantial issue in evolution, because the species will have sufficient medical know how to maintain a low death rate. It's not likely that some individuals will be more likely than others to die because of gravity, so gravity likely won't affect evolution, except over a very long time -- maybe.

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Beat me to it.

Only thing to add really is that environment does have an effect on the body's development, for example if you've lived all your life at low altitudes and then go visit a mountainous area, you'll be huffing and puffing out of breath a lot, but people who have lived there in the mountains their whole lives will be going about with no problem. Also, astronauts in space long-term experience atrophy of their muscles since moving in microgravity requires much less effort.

Probably for the most part the people on the two planets would live very similar lives, but if they go to each other's planets they will notice a substantial difference in what they can do compared to the natives.

BTW as far as height goes, people on Earth are taller than they used to be a long time ago. Don't think I've seen any particular theories as to why, though. Somebody mentioned nutrition, which could very well be it. Availability of good food and basic knowledge of avoidance of illness plays a huge role in general health and longevity.

PervOtaku said:

Beat me to it.

Only thing to add really is that environment does have an effect on the body's development, for example if you've lived all your life at low altitudes and then go visit a mountainous area, you'll be huffing and puffing out of breath a lot, but people who have lived there in the mountains their whole lives will be going about with no problem. Also, astronauts in space long-term experience atrophy of their muscles since moving in microgravity requires much less effort.

Probably for the most part the people on the two planets would live very similar lives, but if they go to each other's planets they will notice a substantial difference in what they can do compared to the natives.

BTW as far as height goes, people on Earth are taller than they used to be a long time ago. Don't think I've seen any particular theories as to why, though. Somebody mentioned nutrition, which could very well be it. Availability of good food and basic knowledge of avoidance of illness plays a huge role in general health and longevity.

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A few notes...

Lowlanders acclimatize to the rarefied conditions at high altitude in about 3 months. The is evidence of genetic adaptation (natural selection) to high altitude among the peoples of the Tibetan Plateau.

In most areas of the world, populations of Homo sapiens are around the same height they were in the historic and ancient past. In Europe, for example, skeletons from Neolithic and Iron age burials are the same stature as current people. We tend to think of them as smaller when viewing artifacts like armor in museums. These look like they were worn by shorter people because the armor is resting on itself rather than being worn by a live person. In the early 1900s, however, Franz Boas did document a significant difference in height between immigrants to the US and their US-born offspring. He thought the greater stature was due to environmental influence such as nutrition and living space.

PervOtaku said:

Beat me to it.


BTW as far as height goes, people on Earth are taller than they used to be a long time ago. Don't think I've seen any particular theories as to why, though. Somebody mentioned nutrition, which could very well be it. Availability of good food and basic knowledge of avoidance of illness plays a huge role in general health and longevity.

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Nutrition is the key to this. It's why average heights have gone up a lot just in the last 100 years or so. 80 years ago Americans were taller than Europeans because we ate better. That's not true anymore, and some European countries, the Scandinavian countries in particular, have caught up to us and passed us in average height.

I'm with the crowd that thinks heavy worlders would be shorter and more heavily boned and muscled. Shorter because they're struggling against higher gravity and leaning over would be more of a strain the taller you are. Also falls would be more dangerous, the shorter the fall, the less damage. After all one would accelerate in a fall faster there than here.

The dog is telling me he needs to go out, better put my shoes on and go.

49greg said:

I'm with the crowd that thinks heavy worlders would be shorter and more heavily boned and muscled. Shorter because they're struggling against higher gravity and leaning over would be more of a strain the taller you are. Also falls would be more dangerous, the shorter the fall, the less damage. After all one would accelerate in a fall faster there than here.

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Not particularly relevant. Earth has giraffes, elephants, wolves, and hogs, all with radically different sizes and bulk.

I'm not sure about this but I would think that in general if gravity were greater living things would be smaller, the reason being that as a living thing gets bigger its mass grows faster than its height or exterior surface area. That's why insects can only get so big, and why whales are much larger than any land animals. If gravity were greater than earth's, the maximum size of given types of animals would shrink. Over time people would be smaller; so would other things. Birds would be smaller because large birds would be unable to fly. Trees would be shorter. Bulkiness would not necessarily be a good thing in a high gravity environment, because, as I noted, as gravity increased the mass:surface area and mass:height ratios would increase.

PervOtaku said:

Not particularly relevant. Earth has giraffes, elephants, wolves, and hogs, all with radically different sizes and bulk.

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There's a lot of variation, but overall, the taller a creature is, the chunkier it will be. You will never see a land animal the weight of a horse with the proportions of a mouse, let alone those of an ant.

Simplifying a bit, the amount of weight that your bones can support when standing upright is equal to the cross-sectional area of those bones. If you keep constant proportions, that area increases with the square of height. But with constant proportions, volume and mass increase with the cube of height. So if you double the height, weight increases 8x but bone strength only increases 4x. Similar issues apply with muscles.

So bigger animals tend to have thicker legs, relative to their body size. Compare a cow's leg bone to a lamb's.

Plausible evolutionary adaptations to heavier gravity are likely to include some mix of:

Creatures get shorter
Creatures get broader limbs (more muscle, wider bones)
Creatures get stronger bones with some tradeoff elsewhere e.g. higher food consumption etc.

I agree that 3000 years is a very short time scale to see this in humans, and short-term physiological effects are hard to predict.

Side note - for a space mission you want small people, because weight is very very expensive.

SimonDoom said:

I'm not sure about this but I would think that in general if gravity were greater living things would be smaller, the reason being that as a living thing gets bigger its mass grows faster than its height or exterior surface area. That's why insects can only get so big, and why whales are much larger than any land animals. If gravity were greater than earth's, the maximum size of given types of animals would shrink. Over time people would be smaller; so would other things. Birds would be smaller because large birds would be unable to fly. Trees would be shorter. Bulkiness would not necessarily be a good thing in a high gravity environment, because, as I noted, as gravity increased the mass:surface area and mass:height ratios would increase.

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FWIW, insects aren't just limited by weight issues. Insects don't have the same sort of circulatory system as vertebrates do; instead of pumping oxygen around the body they rely on diffusion. This does not scale well. Back when the atmosphere was 30% oxygen, we had dragonflies with two-foot wingspans because it was easier for them to supply their tissues.

Weight issues certainly would prevent horse-sized dragonflies in any case, but they run into oxygen limits first.

SimonDoom said:

You mentioned natural selection. Keep in mind that if the species is advanced then natural selection is not going to be a substantial issue in evolution, because the species will have sufficient medical know how to maintain a low death rate. It's not likely that some individuals will be more likely than others to die because of gravity, so gravity likely won't affect evolution, except over a very long time -- maybe.

What's likely to create natural selection pressure on one planet over another is things like food scarcity, dangerous predators, and/or disease. If you can think of a way that higher gravity actually kills people, then it would create selective pressure and cause evolution.

The other possibility is that the species has sufficient know how to guide or cause its own evolution and adapts itself to the gravity via artificial means.

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And don't forget the other part of natural selection, which goes along with longer life. The longer you live, in theory, the more offspring you can produce. But with evolved humans, as well as other animals, the appearance or characteristics of both male and females also tend to affect the number of offspring. There are, sadly, some humans whose personalities, cleanliness, appearance, and abilities will put them at the bottom end of the reproduction pool. Thus not producing the same amount of offspring.

With evolved humans, those traits might even be more important than the traits of fitness for 'survival' that formed our species in previous ages. Thus the reason for so much emphasis on the health and beauty industries - corrective surgeries, well researched diets, exercise, make up, contact lenses, clothing etc.

Oh, and don't forget beer goggles.

Please note that most of my above comments are a bunch of hooey that came off the top of my head while watching reruns of "Rick and Morty" on DVR.

Have growth-vs-gravity experiments been conducted? Have plants and/or cirtters been raised in low- (orbital free-fall) or high- (centrifuged) gravity environments? Such should answer the squat-vs-stretched questions.

As for the surge in USAnian heights over time: I blame growth-hormone-laced McFoods.

I think OP should ask Quora as well, for a greater range of answers.

Based on this I would think lower gravity (pressure) equals taller

Astronaughts grow in space

Did you ever wish you could be just a teensy bit taller? Well, if you spend a few months in space, you could get your wish - temporarily. It is a commonly known fact that astronauts living aboard the International Space Station grow up to 3 percent taller while living in microgravity. They return to their normal height when back on Earth.

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Also look at sea life The creatures that live in deep sea for the most part tend to be smaller than those living closer to the surface.

When a submarine submerges the pressure makes the hull shrink.

Based on my (admittedly limited) understanding of physics, I would think based on the above that Humans on a higher gravity world would tend to be shorter, but if they moved to a lower gravity world their descendants would be normal height.

THis is not due to evolution, it's die to environment. If you want tall, then low G if you want strong high G.