Natural selection meant only 2 in five kids lived to adulthood due to now easily preventable diseases. Natural selection is hardly a concern anymore..
How do genetics determine who you are and how you act?
Culture changes over time. American culture is quite different than the 90s or the 1950s and hose were different than during the Great Depression. Great Britain was different in the 18tu century than in the 19th century, much less today. Mixing of people have been happening for centuries and you'd know that if you read any history.
What success are we suppose to resent? You're whining about how your genetics tell you who you are and how to act.
Immigration has been happening since anatomically modern humans first appeared. You're not being replaced.