[ivanbakel]

Natural selection can only work at the granularity of whole organisms, since they're the things that compete and reproduce. There is no finer pressure on specific concepts like efficiency, except that they may help the organism survive - but whatever solution works for the whole organism, works.

[dredmorbius]

More accurately: of populations of organisms, so long as there's direct genetic transmission throughout that population (e.g., sexual reproduction or possibly if sufficiently prevalent forms of horizontal gene transfer). Heritable differentiation which benefits the population as a whole will tend to be selected for, so long as those aren't overtly nonbeneficial to individuals, and may well explain various non-overtly beneficial adaptations.