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PostPosted: Tue Jan 18, 2011 9:38 pm 
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I was planning on making my Conworld bigger than earth. The gravity would range from 1.2-1.5 times as strong as Earth's, depending on what I finnaly decide on. I basically wanted to figure out what all the implications would be. I understand it would lead to stockier lifeforms, but to what degree? Also, any other effects that don't necessarily pertain to biology?

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PostPosted: Tue Jan 18, 2011 9:55 pm 
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A larger planet will lead to bigger gravity more slowly than you probably think, since you need to consider that gravity decreases with the square of distance. A bigger planet will have its surface be further away from the core, and will therefore have slightly smaller gravity than a same-mass planet with the radius of earth.

Bigger gravity should also mean that plants have a harder time growing, and at some point should prevent forests from being viable. It will also give a huge advantage to water-based things, and make erosion more prominent since rain hits harder when it falls. this should lead to a world where savanna and plains are more prominent, and where cliffs are rare.

Also, you can twist your ankle in such a world

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PostPosted: Tue Jan 18, 2011 10:09 pm 
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The planetary body could be more dense than Earth, which would affect the gravity directly without being mitigated by the planet's radius.

Surface air pressure would be higher. (I'm horrible at gas/fluid dynamics, but I think it would be lower at high altitudes; you could simply put more atmospheric mass on the planet though.) Very lightweight flying things would be able to fly more easily because of that, but larger things like birds would find it difficult or impossible to fly. This would also promote erosion from wind; you wouldn't have a completely flat world, but rather flat areas are more favored.

Large land animals would be more rare: the square-cube law already works against them, but increasing the gravity without increasing their bone strength will make it hard on elephants. You should be able to find the maximum weight fairly easily.


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PostPosted: Tue Jan 18, 2011 10:11 pm 
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This is a concern that I have had with my conworld, since I plan on having humans (biologically compatable, able to interbred producing viable and fertile offspring, thus human but not "terran"). Perhaps I don't wish to deviate too far from Earth norms.

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PostPosted: Tue Jan 18, 2011 10:32 pm 
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Curan Roshac wrote:
This is a concern that I have had with my conworld, since I plan on having humans (biologically compatable, able to interbred producing viable and fertile offspring, thus human but not "terran"). Perhaps I don't wish to deviate too far from Earth norms.


dude, humans on any world that isn't earth or has been colonized by humans, by scientific standards, requires a huge handwaving, so don't worry about that. if there's more gravity, just make them stockier and shorter, and probably with stronger muscles and a huge diafragm and heart as well. And give them beards. short and stocky doesn't work without beards xD

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PostPosted: Wed Jan 19, 2011 1:15 am 
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Ever hear about Korpiklaani? "Wooden Pints" is my favorite song by them.

Anyway, yes, some handwavium is required to make my story work. This is a fact of Sci-Fi, especially the hybrid Space Opera-Cyberpunk universe I'm leading the creation on.

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PostPosted: Wed Jan 19, 2011 2:11 pm 
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Basically the maximum linear size of an animal of a given shape should be inversely proportional to the gravity, if I'm not mistaken. That would mean that your elephants would have to be 1.2-1.5 times shorter.

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PostPosted: Wed Jan 19, 2011 5:01 pm 
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Torco wrote:
Curan Roshac wrote:
This is a concern that I have had with my conworld, since I plan on having humans (biologically compatable, able to interbred producing viable and fertile offspring, thus human but not "terran"). Perhaps I don't wish to deviate too far from Earth norms.


dude, humans on any world that isn't earth or has been colonized by humans, by scientific standards, requires a huge handwaving, so don't worry about that. if there's more gravity, just make them stockier and shorter, and probably with stronger muscles and a huge diafragm and heart as well. And give them beards. short and stocky doesn't work without beards xD


I think Gimli would feel right at home on my planet.

Also, at what point would bipedal organisms cease to evolve? I want to push the limit without eliminating the possibility

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PostPosted: Wed Jan 19, 2011 9:12 pm 
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Depending on atmospheric density, I'd say that bipedalism isn't negated by a high gravity so much as height. I don't think legs work over 3G, however.

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PostPosted: Thu Jan 20, 2011 2:44 am 
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One important thing to consider: higher gravity may mean stockier creatures generally, but some will be stockier than others. There will be a whole range. On this planet, as on Earth, avoiding twisted ankles and broken bones would be just one Darwinian pressure alongside plenty of others. It's entirely possible that your planet could have higher gravity than Earth, and yet have spindlier humanoids than on Earth. It's entirely possible, if they were reacting to a cocktail of evolutionary pressures, some of which rewarded spindly-ness. Too many world builders think "Right, gravity is 10% higher, so my humanoids must be 10% shorter." Nonsense.

Another interesting bit: Planets with higher gravity have atmospheres that lay closer to the surface. The atmosphere may be thicker, but if it's the same as Earth, space would be much closer. We see that with Mars. Its atmosphere is very sparse, but extends very far up.

And as for smaller mountains, on Earth very large mountains and volcanoes are limited by gravity, but I wonder if the same is true of smaller mountains. Is there really any reason why they would be shorter? Surely when tectonic plates collide, they collide just as hard on a high-gravity world. All that rock has to go somewhere.

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PostPosted: Thu Jan 20, 2011 10:31 am 
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Indeed, but the OP is thinking about 20-50% stronger grav... of course, with enough oxygen and muscularity you get pretty agile designs that are big... like a T-rex or allosaurus or stuff, so you're probably right, stocky is ceteris paribus, and that never happens.

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PostPosted: Thu Jan 20, 2011 10:43 am 
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brandrinn wrote:
It's entirely possible, if they were reacting to a cocktail of evolutionary pressures, some of which rewarded spindly-ness.
Such as? What could overrule the problem of falling over, breaking half your bones, and dying?


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PostPosted: Thu Jan 20, 2011 10:55 am 
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hito wrote:
brandrinn wrote:
It's entirely possible, if they were reacting to a cocktail of evolutionary pressures, some of which rewarded spindly-ness.
Such as? What could overrule the problem of falling over, breaking half your bones, and dying?


Starving

Also, we're not talking 10 gees here, just like 50% weight. I've weighted 120 kilo and 87 kilo in the last three years, like a 40% difference, without my ankles and other stuff changing much, and sure, at 120 I did fuck my ankles more, but it's not like I couldn't walk either.

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PostPosted: Thu Jan 20, 2011 11:07 am 
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Torco wrote:
hito wrote:
Such as? What could overrule the problem of falling over, breaking half your bones, and dying?
Starving
So you're saying that animals evolve to be taller because food evolves to be taller? It's a circular argument. Care to try again? Perhaps with more than one word?


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PostPosted: Thu Jan 20, 2011 11:12 am 
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no, it makes sense the way it is

other animals eat the things that are lower, so most of the food that you can get to is higher up

see: giraffes

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PostPosted: Thu Jan 20, 2011 11:39 am 
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Nortaneous wrote:
see: giraffes

Thank you. I was beginning to think that I would have to argue both sides of this issue by myself, since the others seem content to give assertions without supporting argument or evidence, or one-word replies which barely even qualify as assertions.

Now then: Giraffes are the exception. You won't get an entire planet of giraffes. It's very unlikely for your intelligent species to be the giraffe of their world. Furthermore, a giraffe-oid that evolved to eat things higher than other animals could reach would still be shorter, because its competition is shorter, because the competition finds it economically infeasible to adapt to being able to reach higher up due to the gravity increase.

On Earth, the giraffe has extra adaptations because of its spindly nature: a huge heart, high blood pressure, a "miraculous net" to keep the head from exploding when it's lowered to drink, and so on. On a higher gravity world, a giraffe-oid would need even more adaptations, and eventually one of those adaptations would need to be stronger bones so it can support its own weight.

Furthermore, what of the tree-oids the tops of which the giraffe-oids browse? Huge trees are still possible, but higher gravity would favor climbers -- squirrel-oids, say -- over giraffe-oids, since a squirrel-oid only needs to make sure it won't fall off the tree-oid.

This is, as pointed out, a continuum: very tall mountains/trees/animals would be more rare. Shorter things would be more common. Yes, you can have a giraffe, but higher gravity makes things shorter in general.


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PostPosted: Thu Jan 20, 2011 2:25 pm 
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hito wrote:
Now then: Giraffes are the exception. You won't get an entire planet of giraffes. It's very unlikely for your intelligent species to be the giraffe of their world. Furthermore, a giraffe-oid that evolved to eat things higher than other animals could reach would still be shorter, because its competition is shorter, because the competition finds it economically infeasible to adapt to being able to reach higher up due to the gravity increase.

Of course you won't get an entire planet of giraffes; if that happened, some of the giraffes would evolve to be shorter, so they can get to the lower branches more easily and without having to worry as much about the gravity.

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Furthermore, what of the tree-oids the tops of which the giraffe-oids browse? Huge trees are still possible, but higher gravity would favor climbers -- squirrel-oids, say -- over giraffe-oids, since a squirrel-oid only needs to make sure it won't fall off the tree-oid.

I don't know about that; if the gravity is high enough, I'd expect it to be too hard for a squirrel-sized animal to pull itself up a tree.

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PostPosted: Thu Jan 20, 2011 5:37 pm 
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hito wrote:
Torco wrote:
hito wrote:
Such as? What could overrule the problem of falling over, breaking half your bones, and dying?
Starving
So you're saying that animals evolve to be taller because food evolves to be taller? It's a circular argument. Care to try again? Perhaps with more than one word?

how about this

gravity isn't the only factor

five full words

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PostPosted: Thu Jan 20, 2011 6:59 pm 
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Taking another example, we've evolved to have a speech system that was 'deemed' more important than being sure not to choke ourselves when we swallow, which no other animal does because they don't have a descended larynx like we do and their oesophagus and trachea are separate. You'd think that choking to death would be enough for anything not to evolve away from that, but it turned out to be incredibly advantageous when we did.

There are plenty of reasons why a specific species could easily be X height. So things are smaller on average... don't let that stop you from making humans the same height... after all, we're already well above average for our own planet.

Also that kind of circular argument is exactly how evolution works. Plant doesn't want to be eaten → evolves to be taller. Plant is too tall to be eaten → animal evolves to be taller in order to eat plant.

In another example, pandas have evolved by have unconstrictable faces and incredibly hard teeth so that they can eat bamboo. They also spend every waking moment munching away, and don't hibernate, because this is all they eat. You'd think for all that effort they'd go 'fuck this' and start eating meat. Or some plant that's easier to chew. I don't even know why they don't. But they don't. Now say an animal on your planet evolves so that it can only eat a certain kind of plant, and the plant grows taller. It's gonna fucking grow taller or starve, brittle bones be damned. The bones will catch up later if enough brittler folk fall over and die as a result.

Koalas munch on eucalyptus leaves all day, sleep for 22 hours of the day, and don't drink water (because they get it all from the leaves).

Besides, you could get much worse than 1.2 g. I'm reading a book at the minute ('Mission of Gravity' by Hal Clement) set on a world which ranges from 3 g to 500 g, or something (it's also a superhuge planet whose day is 18 minutes long, so it is very, very oblate, causing the distortion). And in the 3g zone the author described a large elephant-like creature with 10 legs (although granted, it was closer to the ground than it would be on Earth), and big forests. OK, so it's all smaller than it would be here, but it's nothing compared to the main alien characters who come from something like a 300 g zone and are basically caterpillars. At 1.2 g there is more gravity and humans would be maybe tired out easier, but it wouldn't create as much of an effect of lesser-sized creatures; only when you take the whole biosphere as an average would such a figure be produced.


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PostPosted: Fri Jan 21, 2011 1:00 am 
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Torco wrote:
hito wrote:
Torco wrote:
hito wrote:
Such as? What could overrule the problem of falling over, breaking half your bones, and dying?
Starving
So you're saying that animals evolve to be taller because food evolves to be taller? It's a circular argument. Care to try again? Perhaps with more than one word?

how about this

gravity isn't the only factor

five full words


Is there as much as one reason why increased robusticity would not be sufficient to adapt to a relatively minor increase in gravity like 20-50%? I experience that much and more from normal car travel.

What's more, working and walking normally in such an environment would increase your skeletal and muscular robusticity, which would protect you from falls; there are also behavioral adaptations to falling that increase the protection garnered from simply living in an environment that experiences a certain amount of gravity. Yes you would hit the ground harder, but you would also be used to it.


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PostPosted: Fri Jan 21, 2011 2:55 am 
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If you don't mind I would like to way in. Dinosuars got bigger because carbon dioxide levels rose. The plants grew faster but less nutritous. The beasts grew to hold more food and suck in more air, as levels of co2 rose they grew. The largest of dinos was still growing. Gravity doesn't play that big a role yet.


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PostPosted: Fri Jan 21, 2011 4:09 am 
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Just to be annoying, let me also point out that there is no particular reason why animals should evolve to have legs. The could just as well have, say, wheels, or they could be stationary, or they could all swim or fly, or they could be composed of massless particles...

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PostPosted: Fri Jan 21, 2011 11:50 am 
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Chuma wrote:
Just to be annoying, let me also point out that there is no particular reason why animals should evolve to have legs. The could just as well have, say, wheels, or they could be stationary, or they could all swim or fly, or they could be composed of massless particles...


This topic shows what I plan to do.

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PostPosted: Sat Jan 22, 2011 2:32 pm 
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I have a blog post on the response of human beings, evolved for one gee, to life in various gravities. It has a diagram with one fairly reasonable estimate as to the variation of human morphology.

I intended to throw it out really quickly in response to this thread. It took quite awhile to put together, but at least it looks like it was thrown together on the spur of the moment :roll: .

Basically, human size is unlikely to vary in a linear manner with gravity.

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PostPosted: Sat Jan 22, 2011 3:31 pm 
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