It's an odd science story, which make people go and ponder upon things.
After Scott Kelly went off into space for roughly eleven months.....he returned. He has a twin brother. DNA-wise, the two should match up very closely. After the trip though....they took another DNA test of Scott, and came to this odd conclusion.....SEVEN percent of his DNA changed after this trip. The general things that changed? The immune system, DNA repair structure, bone formation networks, hypoxia and hypercapnia.
If Scott had made two or three trips over a decade period? There's probably a heck of a lot about the DNA structure of Scott that would be totally different.
So, we come to this topic of science conversation. Any serious space travel....means that your DNA changes....for better or worse. If you did go off on some seven-year adventure....you would return in a very different way, with probably more than a quarter of your DNA revamped, and it would lead to general expectations going to some far extremes.
But using this same logic....it means that some other folks (aliens, if you like) are stuck into this problem as well, and if they went off on some great fifteen year expedition....their DNA wold be modified and changed as well. In fact, if you hauled a dog aboard the space ship....you'd find their DNA swapped around and changed as well.
While the PhD guys avoided the topic....you'd sit and pause over the next issue....plants have DNA as well. If you blasted a dozen plants into space for a year....would all of them be altered as well? The odds are....yes.
The odds of vast space travel ahead for humans? Once you admit that your body is undergoing constant 'renovation' upon itself, and medical folks can't predict how they'd treat these things while on a voyage....the idea of vast space travel will likely go away.
