It's that second one. Geneticists talk about genes being "conserved" when they are needed, and use the level of conservation to understand how essential a gene is to the functioning of an organism. For example, hemoglobin genes are highly conserved across all animals, because any mutation there is likely to produce an unviable organism.

If something is not conserved by selection, then the default is for it to be overwritten. So more like "need it or lose it". But I feel like that's pretty close to the article's phrasing.