Tribal Betrayal - Tribal Loyalty, Biden vs. Trump

How did the behavior of Tribal Betrayal survive in human evolution?

Joe Biden:
“Folks like me who are Caucasian, of European descent, for the first time in 2017 we’ll be in an absolute minority in the United States of America, absolute minority. Fewer than 50% of the people in America from then and on will be white European stock. That’s not a bad thing, that’s a source of our strength."
Key to U.S. economic strength is the "constant, unrelenting stream” of immigrants into the country. “Not dribbling,” Biden said. “Significant flows.”
https://www.foxnews.com/politics/flashback-joe-biden-constant-unrelenting-immigration