The Modern Synthesis as a Limited Consensus 545
higher-level selection based on features of populations that cannot be explicated as
additive results of organismal properties—in other words, "emergent" characters.
He correctly defines a population ripe for selection at its own level as "an inclusive
entity with emergent characteristics that transcend the summation of the attributes
of the component individuals" (1960, p. 307).
But, having legitimately defined the problem, he then launches into an almost
rhapsodic, and simply illogical, claim that almost anything with definable
boundaries can be recognized as a unit of natural selection: "Natural selection
operates at each level of integration from the gene and complex polygenic
characters within the individual, to the whole individual, and to various levels of
intraspecific population systems and interspecific inter-adapted community
systems and ecosystems" (1960, p. 340).
This argument can be defended in theory so long as the higher unit operates as
an interactor with surrounding environments and remains in a genealogical nexus
engaged in differential reproduction (see Chapter 8). But how can Darwinian
selection possibly operate directly on an ecosystem? However we may choose to
define such an entity, ecosystems do not mate and do not produce children (see
Chapter 8, pp. 597-613 on criteria of Darwinian individuality). No argument can be
made about their differential reproductive success, and no Darwinian calculus can
therefore be applied to their history through time.
Emerson doesn't seem to grasp that selection works by differential
reproductive success, not by design for immediate, self-serving utility: "It would
be extremely difficult," he writes (1960, p. 319), "to explain the evolution of the
uterus and mammary glands in mammals or the nest-building instincts of birds as
the result of natural selection of the fittest individual." But if milk-rich mammary
glands promote the survival of offspring, then the mother acts in her own
Darwinian interest. In short, Emerson's paper gives us an unintended insight into
the confusing lack of definition that natural selection has always suffered, even at
the moment of its greatest explicit influence.
Second—and more important in its virtual ubiquity—leading evolutionists,
though well aware that orthodoxy identified individual organisms as the focus of
selection, did not grasp the logical necessity or centrality of such a claim in
Darwinian theory, and therefore often indulged in vague, perhaps unconscious, and
often fuzzy, statements about the efficacy of higher levels. (I say "fuzzy" because
most of these claims about populations and groups only invoked the non-emergent
effects of organismic characters—and therefore do not necessarily qualify as valid
statements about higher-level selection. I don't think that many evolutionists had
properly formulated this crucial issue at the time.)
Dobzhansky, for example (1957, p. 392), states that selection operates on
organisms, but then proposes that such phenomena as heterozygote advantage
might record some populational "extra" in exposing the reduced fitness of
homozygotes as a kind of organismic sacrifice "for" the group: "Natural selection
operates through differential survival and differential fertility of individuals,