Dr Alessio Fassano, a world renowned researcher on celiac disease, said recently that even travelling from one continent to another changes your gut microbiome, and for some people this exacerbates autoimmune disease.
This made me think that if that’s true, then there’s no way in hell that we will ever be able to colonize other Earth-like planets. Not even if we terraform them. Humans require very specific bacteria & yeasts to stay alive, we are actually a shell made out of these colonies. We are not “I”, we are “them”, science has found in the last 3-4 years. Some doctors now wonder if we’re “humans with trillions of bacteria within us, or bacteria having a human experience”. Ponder on this for a second.
So just because a planet might have good levels of oxygen and gravity won’t mean sh*t. We won’t be able to leave our space suits and sealed colonies to just breathe that air. IF we do, and IF we survive that (I don’t believe we can), then in a few generations these people won’t be humans anymore. They’ll be something else.
In that light, I believe there are only two ways to visit “other places” out there. One, is a hybridization program. You make a hybrid between a native species, and humans. It’s possibly the way we’re going to go. Second way is to never leave your planet, learn to live sustainably here, and then visit other worlds with mind alone (e.g. meditation). Now, that second method is a more “out there” than most people feel comfortable with, but it’s the least intrusive method.
I, too, wish that the sci-fi wishiful thinking of simply finding a “habitable” planet was possible, but I just don’t see it happening. And that’s not because there aren’t any Earth-like planets, or that we don’t have the right inter-stellar travelling technology for it. I feel these are easier problems to solve than going around the problem of gut microbiome and actually surviving on a planet that we weren’t evolved with.