Natural Selection and its limitations

On p.179, "Natural selection will modify the structure of the young in relation to the parent, and of the parent in relation to the young. In social animals it will adapt the structure of each individual for the benefit of the community; if each in consequence profits by the selected change. What natural selection cannot do, is to modify the structure of one species, without giving it any advantage, for the good of another species". Although natural selection does, in fact, increase the survival abilities of plants and animals, Darwin writes that with this change also comes advantages to other species. Although this isn't necessarily a bad thing, it does limit the effect to which one species can increase in relation to one another. It makes extinction much harder, and therefore aids the natural progression of specie developments.