You know what happens when a caterpillar goes into it's crysilis? You'd think that it would slowly become a butterfly, one day it get antenna, then wings and whatnot. You'd be wrong. The entire caterpillar turns into mush. Only it's central nervous system remains as out of a soup of genetic material a butterfly is formed. Lets leap ahead in concept here, and say that human bodies are ill adapted to interstellar travel. It would be better to put your brain into an engineered body then try to adapt to every planet you come across. Able to breath more then oxygen, denser bones, better sight and hearing, these are all on the table. It also might be that other aliens need these bodies as well, and a general set of guidelines have been established, being basically humanoid in nature. It would explain why aliens always look like humans in make up. The new bodies would obviously need to have ridges for certain brain types, or pointed ears to better hear interstellar frequencies. I don't have to draw a map here. But what would you call this process, and this new body?