people have a hard time grasping this concept for some reason.
my favorite example to illustrate this is the trait of being poisonous. if evolution cared about species and then every single one would be poisonous and all predators would have to hyper specialize in prey (arms race between a particular poison and its resistance). it's precisely because it's so difficult to elicit a benefit from this strategy for the lineage that it's so rare. almost always a mutation in coloration has to happen to set the lineage apart from the others first. and then the lineage has to survive the disadvantage long enough.
> acts on the molecular, cellular
this is rare and even more difficult to understand.https://en.wikipedia.org/wiki/Structural_inheritance
basically, the genes do not generally contain blueprints but rather processes utilizing existing cellular machinery. a "mutation" can occur in a machine which will allow a propagating difference.
and there is nothing special about populations. it's merely the only way to observe most changes. gene frequencies in gene pools.