A new study based on astronauts Scott Kelly and Mark Kelly—identical twins—found that space travel can alter DNA, at least the way we’re doing space travel now. The study found that 7% of Scott Kelly’s DNA did not return to normal after a one-year mission in space. Gizmodo noted that the change is epigenetic in nature, rather than simply genetic. It’s the way Mr. Kelly’s genes are expressed, not the genes themselves, otherwise he would now be a new species. Important semantics aside, the changes were thought to be caused by “oxygen-deprivation stress, increased inflammation, and dramatic nutrient shifts that affect gene expression,” according to CNN. It’s important to both understand and solve these kinds of issues when it comes to prolonged space flight, travel to Mars, and other space-related activities, and the Kellys being part of this study will pay untold dividends towards that understanding. The video below on the topic is from NBC.