“Low Gravity Makes You Tall”

A common idea in much of science fiction literature is that those otherwise normal humans who are raised in lower gravity environments (Mars, on the Moon, or even zero-g space stations) will be taller. The idea is that without Earths crushing gravity, a persons bones will grow longer. Commonly (like in John Varley’s “Rolling Thunder,” which I just finished) authors posit Moon/Mars-raised humans being about 20% taller than Earth-raised. That would turn these pioneering folks…

Into either these people (assuming a purely vertical “stretch”):

Or these people (assuming a 3-D scaleup in all dimensions):

Personally, I doubt it, or at least I doubt that it would make a meaningful difference. Those who have spent extended periods in zero-g *have* come home taller, due to the relaxation and expansion of the softer materials in the joints in the spine; but in time they squish back down.

Since we have not, sadly, given birth to whole generations in space (and it’s a damned crime that we haven’t… let’s face it, had we not cheaped out in 1968, but instead made an actual effort, we could have had permanent space settlements of some sort by 1980… and the kids born there would now be THIRTY FRICKEN’ YEARS OLD by now, with kids of their own), this is a tough one to test. My recommendation for those *truly* interested would be to examine the records of those who spent their whole lives bedridden due to disease or paralysis, from childhood to adulthood. These people have not spent their lives being squished by gravity in the normal standing direction, and thus should demonstrate the supposed lengthening of bones.

One area that’s typically *not* examined with sufficient criticality is the arm. Rather than spending time standing around being compressed by the weight of the body, the human arm typically just hangs there… in tension. So if lower gravity would result in bone length change in bones that are normally compressed, then this same effect should also work on bone that are normally in tension. But here, since the tension is reduced, this should make the arm bones *shorter.* So here, kids, is roughly what these superbeings, these gods among men, would look like:

Urrrrmmm…

To me, these look like long-legged dwarfs (Midgets? Little people? Whatever the hell the PC term is these days). Note that with leg and torso stretched 20% and arms shortened 15%, you wind up with a whole race of people who can’t… hmmm. In an effort to avoid causing any possible offense to delicate reader sensibilities, what’s a good euphemism for “wipe their own asses?”

Additionally: notice that apart from the arms, I didn’t do differential scaling of the bits and pieces. Such as the heads. Would the skull get bigger? If so, why? The underside of the skull only needs to support the brain, and the sides and top obviously don’t need to support even that much. So the skull is not exactly getting crushed out of shape by gravity. And lets face it… the guys nads aren’t getting stretched (well, not by gravity at any rate). And there’s no real gravity stress on the hands, and while the foot clearly is under a great deal of weight, the length of the foot would not seem to be gravity-driven. So, the final sketch shows 20% stretched legs and torsos, 15% reduced-length arms, normal heads (which now look tiny), necks, hands (which now look huge), feet and nads (which now look… well…).

Ick.

And this is why “low gravity makes you tall” is a feature of science fiction literature, but not so much science fiction TV or movies, or even art. Because if low gravity causes your bones to grow differently, you’re gonna wind up goofy lookin’.