Specifically if you never go back to regular gravity. Ex: you go to live on another planet with say 3/4 Earth’s gravity and never return to Earth.
They did an experiment with two astronauts, both twins and well experienced… One twin spent a whole year on the ISS in low earth orbit and the other stayed on earth. Surprisingly, when the brother returned to earth, his DNA had altered from that of his brothers.
We don’t know exactly what is going to happen in the long term, we can only predict. But there will be changes, and they will be negative when it comes to living back on earth. The experiment proved that space will change us, we just don’t know exactly how it will.
A person cannot evolve in a single lifetime, only change physically due to external influences. So we don’t know if it may eventually prove fatal if someone stays in space for a lifetime. It will be that we have do it gradually and generational to ease people into the changes. Or alternatively we would have to genetically modify and create “longhaul space humans” or humans modified for a certain planet. All of which would probably not be able to survive on earth if altered enough.
It’s all very sci-fi and speculation atm, plus we are a long way off playing god with the ethics and technology involved.
Assuming you take a living thing from Earth and move it somewhere with lesser gravity…
– … the muscles and bones are no longer exercised by gravity and will atrophy
– … blood and other fluids will no longer flow properly as the circulatory systems account for gravity
– … the heart, no longer affected by gravity, will change shape to a more oval form and suffer more frequent faults
The Soviet Union’s space experiments have shown that these effects are mitigated by increased exercise, allowing astronauts to withstand microgravity for about a year.
A lot of these answers only concern microgravity in space. If we could colonize Mars, it would be a lot different. There would be gravity and I don’t *think* your bones and heart would waste away. You would be lighter and your muscles and bones wouldn’t need the strength they do on earth. I think the Expanse did it pretty good, although I’m not counting the Belters, that’s a bit more extreme. Again that is just my theory so feel free to knock it down.
A few examples:
Your heart has evolved to pump your blut up to your Head against gravity. With lower gravity, the blood pressure in some parts of your body will be to high and in others (the legs for example) to low.
Your bones loose density. This leads to them breaking more easily.
Your muscles will reduce, wich further increases risk of injury and this might also increase risk of heart failure or breathing problems.
Your eyes probably will get worse, because they would have higher internal pressure (because of point 1)
Your body will react to the high blood pressure by reducing the total amount of blood cells beeing produced, but this won’t fix the blood pressure problem, but will cause more problems.
In short: people in low gravity will get sick more often, will be weaker (in strength and impunity to sickness) and thus probably won’t get as old.