“The complex of problems falling under the ‘levels of selection’

rubric includes an intriguing mix of empirical, conceptual and

philosophical issues. Roughly speaking, the key question concerns the

level of the biological hierarchy at which natural selection occurs.

Does selection act on organisms, genes, groups, colonies, demes,

species, or some combination of these? Evolutionary biologists and

philosophers of biology have devoted considerable attention to this

question over the last forty years, so much so that in some quarters

the debate is now regarded as stale. Despite this perception, recent

years have in fact seen interesting and important new work on the

levels of selection, some of which has significantly re-defined the

terms of the traditional debate. This paper aims to introduce the

reader to these new developments.” — Samir Okasha, Human Nature Review 2003 3:349-356