What third party?!?
The people deciding whether or not you get to breed even though they’re not in competition with you for a mate. Natural selection is all about direct interaction, you acquire food and live longer or you don’t, you become food and help something else live longer or you don’t, you acquire a mate and carry on your genetic traits or you don’t. Eugenics is all about indirect interaction some third party is deciding who breeds and who doesn’t, heck they might even go so far as to decide who gets to eat and who doesn’t.