On gravity and human endurance

[Zor]

This is a fairly basic question that i want to ask in regard for purposes of worldbuilding. Here we have some basic members of H. Sapiens Sapiens without any fancy genetic engineering or cybernetic re-inforcements or stuff like that. For perminant living what would be the upper limit of gravity said people could take and fuction more or less normally?

Zor

[Mayabird]

What do you mean by normally? People will have higher death rates in high gravity because their hearts will have to work harder at pumping blood everywhere. A lot of accidents would be more dangerous as well, like falling. It probably depends on what people consider acceptable losses. People back in the day (and still in a few very bad areas) considered normal to be dying before age 40.

[Oskuro]

I guess he means at wich point teleporting into said planet would result in instant death or incapacitation.

[Bedlam]

I've been meaning to ask a similar question recently. I was thinking on what gravity range would it be possible to set up human colonies on without genetic engineering or huge amounts of equipment. So what gravities could you live resonably confitably for atleast 30-40 years and have children on.

[Temujin]

There was a past thread about something like this with, I believe, a link to an official site outlining the various extremes of gravity, atmospheric pressure, etc. that a human could reasonably adapt to unaided. I thought I had it booked marked, but can't seem to find it now. I'll post the link if I can find it.

[Broomstick]

I seem to recall participating in that thread as well. I'll try looking for it as well.

An important factor is whether people will be given time to acclimatize to the increased gravity, or will suddenly have to deal with it all at once. I suspect having some time to acclimatize (perhaps by living in a gradually accelerating centrifuge sort of arrangement) would result in a higher tolerable gravity, as it would give the body time to adjust and strengthen muscles, bones, and the cardiovascular system.

I'm taking a wild ass guess here, but I'm assuming 2 g's is tolerable. After all, we do have examples of people twice normal body weight for their size living a fairly normal lifespan. It's not entirely the same thing, as presumably for the 2 g dweller more body mass would be muscle and less flab, but it does seem that the human body can accommodate twice normal body weight. I'd also expect some physical issues, such as blood pressure problems and joint problems. In theory, I'd expect less osteoporosis as weight bearing seems to deter that.

Right now, though this is a theoretical concept as no one has tried living long term in higher than 1 g (that I know about).

[Serafina]

Why i can't say anything about an upper limit, the lower limit is pretty clear:
You can live just fine in zero G pretty much indefinately.

You will get into trouble if you ever want to visit a planet, especially if you do not train properly (and even then), but life functions just fine without any gravity at all.

[Oskuro]

I was wondering, could the negative effects of high gravity be mitigated somewhat by having people spend some time (for example the time spent sleeping) inside water? Sort of like the tank Luke was submerged into in Empire Strikes Back, with a breathing mask attached, yet completely submerged.

Not sure if it would help the circulatory system, but muscles and joints would have more time to regenarate damage, I guess.

[Junghalli]

Obligatory Great Mambo Chicken Experiment mention:

There was the hyper-G work done on chickens, for example, by
Arthur Hamilton ("Milt") Smith in the 1970s. Milt Smith was a gravity
specialist at the University of California at Davis who wanted to find
out what would happen to humans if they lived in greater-than-normal
G-forces. Naturally, he experimented on animals, and he decided that
the animal that most closely resembled man for this specific purpose
was the chicken. Chickens, after all, had a posture similar to man's:
they walked upright on two legs, they had two non-load-bearing limbs
(the wings), and so on. Anyway, Milt Smith and his assistants took a
flock of chickens -- hundreds of them, in fact -- and put them into
the two eighteen-foot-long centrifuges in the university's Chronic
Acceleration Research Laboratory, as the place was called.

They spun those chickens up to two-and-a-half Gs and let them
stay there for a good while. In fact, they left them spinning like
that day and night, for three to six months or more at a time. The
hens went around and around, they clucked and they cackled and they
laid their eggs, and as far as those chickens were concerned that was
what ordinary life was like: a steady pull of two-and-a-half Gs. Some
of those chickens spent the larger portion of their lifetimes in that
goddamn accelerator.

Well, it was easy to predict what would happen. Their bones
would get stronger and their muscles would get bigger--because they
had all that extra gravity to work against. A total of twenty-three
generations of hens was spun around like this and the same thing
happened every time. When the accelerator was turned off, out walked
. . .GREAT MAMBO CHICKEN!

These chronically accelerated fowl were paragons of brute
strength and endurance. They'd lost excess body fat, their hearts
were pumping out greater-than-normal volumes of blood, and their
extensor muscles were bigger than ever. In consequence of all this,
the high-G chickens had developed a three-fold increase in their
ability to do work, as measured by wingbeating exercises and
treadmill tests

Going by that, 2.5 G should be tolerable.

[Sky Captain]

While humans maybe could adapt to live in 2G enviroment what about doing hard physical labor in that environment? Living like just walking around and sometimes moving some light stuff is one thing. But imagine if you have to walk long distances while also carrying some heavy gear like on an expedition in jungle where terrain is too broken for vehicles. I think it would be nearly impossible for anyone who hasn't lived in that 2 G environment his entire life and evolved enough reserve strength to handle such extra loads.

[Broomstick]

Even if someone HAD lived their entire life in 2 g's they probably would not be able to carry as much mass or exercise as long as someone in 1 g. The human body evolved for 1 g. If we can adapt to 2 g's that is because we are adaptable, that doesn't mean we'd function as efficiently.

Certainly someone raised in 2 g's would have an advantage over someone raised in 1 g and having to adapt later. It's probably analogous to high altitude - the native Tibetans (who not only live their lives at high altitude but actually have some small genetic advantages) do better than lowlanders. Nonetheless, Tibetans Sherpas still usually use oxygen to summit Everest, just like anyone else. There are definite limits to human tolerances.

[Alerik the Fortunate]

Well, I imagine also, still barring significant gene modification, that over numerous generations you'd probably have selection pressures for people with physiologies better adapted to high g environments. After 500+ years on this colony, you may have a portion of the population that functions nearly as well in 2g's as a baseline human would in 1g (maybe it would take longer, I have no expertise in estimating time frames for this sort of thing).

[Junghalli]

Well, I imagine also, still barring significant gene modification, that over numerous generations you'd probably have selection pressures for people with physiologies better adapted to high g environments. After 500+ years on this colony, you may have a portion of the population that functions nearly as well in 2g's as a baseline human would in 1g (maybe it would take longer, I have no expertise in estimating time frames for this sort of thing).

Well, evidence indicates that most Europeans were lactose-intolerant 7000 years ago, so that should give a lower limit to how quickly a selective sweep of an advantageous mutation can happen in humans.

I'd expect after sufficient time on a high-G world you'd get a race of humans with adaptations paralleling the Great Mambo Chicken physique: less body fat, more powerful hearts, bigger muscles, maybe denser bones. Probably they'd get shorter too: a smaller body would inherently be less work to move around, and it would make falls less potentially harmful.

[Serafina]

Well, evidence indicates that most Europeans were lactose-intolerant 7000 years ago, so that should give a lower limit to how quickly a selective sweep of an advantageous mutation can happen in humans.

Actually, you could call that "weak selective pressure". It was advantageous, but you did not die if you did not have that trait (not being able to digest lactose).
As opposed to strong selective pressure where you die when you don't have a trait.

That should have a significant impact on how fast a treat spreads, if only because strong pressure reduces the population.

[Broomstick]

A trait that kills the owner is only strongly selective if it kills early - if it kills you at 50, after you've reproduced several times, the selection pressure is much weaker than if it killed you at 25 and cut short your reproductive years.

[Purple]

What about artificial selection? You know, only the best adapted get to produce offspring.
Or, maybe more likely, the best adapted have to produce much offspring while the less adapted are only allowed 1 child to preserve minimal genetic diversity.

With a sufficiently large population it could eventually produce a results far faster.

[Broomstick]

It wouldn't require genetic engineering. Those who come from families who live longer under 2 g's should simply have more children. This might not even need to be legislated - under such a hypothetical situation those who endure 2 g's better and live longer (or come from longer-lived families) might be seen as more desirable mates and thus be likely to reproduce more often and more successfully.

That, by that way is NOT artificial selection, it is sexual selection, that is, choosing a mate based on specific criteria which may or may not be arbitrary.

[Purple]

That, by that way is NOT artificial selection, it is sexual selection, that is, choosing a mate based on specific criteria which may or may not be arbitrary.

No, sexual selection is what you suggest eg. a system without fixed legislation.
What I suggest is cattle like controlled reproduction including artificial insemination and abortions to ensure genetic quality. There is a difference.

[Broomstick]

Yes, your method is coercive as all hell and would likely lead to rebellion. Oh, wait - that's right, you favor police states.

Why don't you just engineer personal initiative and free will out of the populace, too, while you're at it. Would make things ever so much easier for the rulers of your little cesspit.

Tell me - would you consent to having your balls removed and your only biological children created at the whim of the all-powerful state? Or are you assuming you'll be one of the ones in charge?

[Purple]

That depends on the situation.

If the conditions were such that a group of colonists has to stay alive in a hostile environment like 2-3Gs and possibly domed cities, a hostile ecosystem and what not you would be able to ideologically justify it.

This is especially true if we are in a non FTL environment where they can expect resupply in many years if not decades or even centuries time (if at all) and absolutely have to become self sufficient. In that case I can clearly see my method as being chosen and employed and even being used as an ideological tool to bind people together. Sacrifice everything for the sake of the future.TM


On the other hand, if it is a quite hospitable little place with earth like conditions (other than the gravity load) and FTL resupply to the colony is readily available, friendly natives and plentiful game and plant life to live off than it would be a foolish notion.


It all really depends on the conditions of the story and that is not up for debate right now.
What you can't deny however is that under certain conditions such measures could be used to produce valuable results and that because of this they should not be discarded even if they do not match your carefully crafted sense of morality.

[Alerik the Fortunate]

You did somewhat dodge Broomstick's question in that you won't answer it from a personal viewpoint: would you personally accept being judged the genetic undesirable and effectively castrated? How people respond emotionally determines whether authoritarian cattle breeding of humans is really viable. Though I suppose that you could assume that all the colonists are already under psychoactive drug regimens placing them under complete control of the colonial authority.

This brings up another point: what is the composition of the colonists? Presumably there were robotic expeditions or reasonably accurate long distance observation of the destination world before the colony ship was launched, otherwise how would they have any idea what to prepare for? Were the colonists pre-screened for genetic predispositions most favorable to what was known about the conditions on the destination world? Were they selected primarily for useful technical skills? Are they all political/ideological cultists dedicated to promoting the group ideology? Are they a diverse group, physically or culturally?

Anyway, it seems that we don't have much hard evidence for very long term exposures to elevated gravity in humans, since most work seems to be focused on maximum survivable forces over relatively short durations, and maintaining lifelong g-forces on Earth is quite impractical. Though this mentions that negative g's and forces from different directions have much more serious effects than vertical or forwards/backwards oriented forces. So it might affect people's behavior in some ways: no more headstands on a 2g world. Acrobatics as we know it will fade from the culture.

P.S. Purple: though it may be an aspect of your inscrutability, "thou shall" should be conjugated as "thou shalt".

[Purple]

You did somewhat dodge Broomstick's question in that you won't answer it from a personal viewpoint.

But I did, I said that under certain conditions everyone and not just me would accept that.
Maybe I was not clear thou so for the official record:
My opinion on the justification of such measures should they be presented upon me would fallow the paten described in my last post.

So if the society is in a state of hardship and I had to give up having children for the sake of the future I would. I would maybe not be too happy about it but I would accept the survival future generations as a worthy goal.


But as everything it is higly conditional. We don't know what kind of colony it is, what kind of planet it is, what the composition of the colonists is, what preparations were made, what the culture and social structure of the society that sent the colonists there is, what the purpose of it is or any other factor.


All I said is that under certain conditions this sort of actions could be used and is not to be discarded as impossible.

P.S. Purple: though it may be an aspect of your inscrutability, "thou shall" should be conjugated as "thou shalt".

Thanks, will correct it. I am not that good with such thigns as you can see.

[Junghalli]

A Russian experiment with domesticating foxes produced significant differences after 50 years of selective breeding (ref). Foxes live 10-12 years in captivity and an average of 3 in the wild (ref), so call it between 5-33 generations. For humans that might correspond to anywhere from 125 to ~1000 years, depending on which number you use and what you assume average generation time is.

You should probably be able to produce faster results with artificial selection than natural selection, since artificial selection generally works by creating pretty extreme selection pressures.

As far as ethics goes, I'm not really going to get into that but evolution selecting for people better able to tolerate high Gs wouldn't exactly be a pleasant process either. It would be people without the advantageous genes dying earlier of high G related health problems or in accidents. Leaving aside implementation issues (which, granted, are huge), restricting everyone but those with advantageous genes to one child strikes me as a solution that could easily create less suffering - selection by people being born and then dying early creates suffering, selection by some people being encouraged to have more or fewer children does not inherently do so. Proper genetic engineering would nicely avoid most of the potential ethical issues with selective breeding of humans, of course.

[Broomstick]

You did somewhat dodge Broomstick's question in that you won't answer it from a personal viewpoint: would you personally accept being judged the genetic undesirable and effectively castrated?

It's not just that - he was talking about using artificial insemination and abortions - that is, treating women like we do cattle, without any mention of what restrictions, if any, men are under. A typical male blind spot, to be eager to restructure and control female reproduction without imposing limits on their own..

Really, there's a lot to be said for freezing ample sperm samples of men, performing vasectomies, then allowing unlimited sex (in a small colony you don't want men, particularly young men, sexually frustrated). In other words, totally disconnect sex from reproduction. Thus - conception solely through artificial insemination, so there will be no need for abortions (save for medical complications). You could even engineer such a society so that men have to earn the right to reproduce - perhaps they have to live to 50 before their sperm is used to father children - or otherwise demonstrate their fitness. It would certainly give them incentive to work hard and make positive contributions to society.

In fact, if the colonist bring lots of frozen sperm they'll have less trouble maintaining genetic diversity.

That is, of course, assuming conditions are such that such strict control is required.

[Purple]

It's not just that - he was talking about using artificial insemination and abortions - that is, treating women like we do cattle, without any mention of what restrictions, if any, men are under.

Well firstly, the abortions part was used in countries in our world (I think, but am probably wrong with at least 99% probability of being wrong) in case of birth control laws and we know it is used in our world in case of ultrasound detected heavy birth defects (abit with a choice for the parents).
And artificial insemination means that when a couple wants a baby and the male is "incompatible" they go to a clinic rather than doing it them self.

I was not actually advocating peening women up and force-sexing them you know...
You make me sound like some tyrant from a bad manga plot.

A typical male blind spot, to be eager to restructure and control female reproduction without imposing limits on their own..

You clearly underestimate the effect upon a male when he knows that he can not have children. Sure there are more things to life than having kids but the emotional stress is still there.

And just how do you say that being forbiden to have kids is "without imposing limits on male sequality".


Other than that the things you say is generaly what I say as well (part from the humiliation and what not).

Provide free but mandatory contraception and have babies only be born from selected preferred gene stock and than adopted by the families.

In the end, every family could get a child, just not every child would really be yours.

Also, you raise some very valuable points about incentives in such a society. Separate sex from procreation and you can make procreation into the ideological duty of the select few best thus making others strive to be like those best.