Can races die out?

So I have a world I’ve had for a while and it’s an all human world but I’ve noticed that everyone is light black and no one is white so do some ethnicities just die out over time or is this some kind of anomaly?

So I have a world I’ve had for a while and it’s an all human world but I’ve noticed that everyone is light black and no one is white so do some ethnicities just die out over time or is this some kind of anomaly?