I prefer to think that the people that will live on Mars for example, or travelling to other stars, will be able to adapt and evolve differently. Of course it is not easy. But it will be possible. They won't be able to go back to Earth and live with that strong gravity. Many will die, but some of them will evolve. Look at all the diversity of animals on the planet constantly evolving. Humans are no different. It's like telling a minnow... you are never going to be able to live outside the sea, in that solid rocks out there... don't go there you will die !!! You will never be able to breath out there or have legs to walk. One thing is sure... a minnow cannot become a whale in just one day hehe Give it time... a lot of time ;-)