Why should we choose the United Nations of Earth for our first game?
Because aliens disliked the United Nations of Earth. Playing it on your first run meant losing a huge amount of goodwill with aliens, getting ganged up on by them early in the game, and ending your wicked life right there. (Ironman mode only.)
If you got crushed in your very first game, your morale would crumble too. Better to stick with the United Nations of Earth. Xenophilia improved aliens' opinion of you, so they would leave you alone and let you build up peacefully.
You wanted to play the United Nations of Earth and build up peacefully? Were you kidding? Wasn't the whole point of playing it to wage early wars?
Early warfare and peaceful development were completely different playstyles. If you didn't know how to play, just stick with the United Nations of Earth, lest you step into the Sea of Stars only for a Fallen Old Bastard to take offense at your policies and beat your national pride out of you in three blows. "Sir, I'm from the United Nations of Earth!"
Because of its xenophilic nature, the United Nations of Earth would sooner or later accumulate a collection of alien species within its borders. You would see a whole bunch of species appear in the pie chart on your demographics screen, commonly known as the color palette.
Suppose you had already established diplomatic contact with several nations and signed migration treaties, bringing lots of alien pops into your country. You would then need to manage those aliens.
So find the species screen in the UI on the left and open it.
Your primary species was, of course, human. You could easily find humans on the species screen, where you could also see their corresponding