The way I understood evolution wasn't that "some mutations will have a positive impact", it's more like, when a species hits hard times, "some mutations allow i

The way I understood evolution wasn't that "some mutations will have a positive impact", it's more like, when a species hits hard times, "some mutations allow it to survive long enough to reproduce". Sure, you have dominant genes like eye colour. But evolutionary changes to a whole species are more about weeding out genes that cannot survive, right? Because if a species has no specific sexual selectors for breeding and all mutations survive and reproduce, then how does a specific gene thrive? Edit: but chatting to my wife, she mentioned that species is a difficult concept, generally taken to be a generic group that actual mate in the wild. There are several different species that could technically produce offspring but through sexual selection, do not.