Philosophy of Biology

LEVELS OF SELECTION

Robert A. Wilson

1 INTRODUCTION

The generality of the theory of natural selection is both a virtue and, if not quite
a vice, at least the source of much spilt ink, spirited discussion, and occasional
despair. The theory of selection is general in that the conditions usually held to
be necessary for natural selection to operate — that there be heritable variation
in the fitness of some trait within a population — is itself neutral about just
what entities natural selection operates on. This kind of neutrality has provided
evolutionary biologists with much room in which to develop the theory of natural
selection, giving rise to “universal Darwinism” [Dawkins, 1983; Dennett, 1995], to
both dualistic and integrative accounts of natural and cultural selection [Durham,
1991; Boyd and Richerson; 1985; 2004] and to debate over the levels of selection.
It is this final issue that will be our focus in what follows. Sections 2–5 will cover
basic issues and views in this debate, while sections 6–8 will take up some more
specialized topics that are of current debate: pluralism (section 6), the conception
of groups (section 7), and evolutionary transitions (section 8).
If the Darwinian theory of natural selection is neutral in the way the people have
typically thought that it is, then there is a real question as to what the agents of
natural selection are. What are theunitson which natural selection acts? Darwin
himself formulated his theory of natural selection withorganismsin mind as the
principal (and near exclusive) unit of selection. They were the bearers of the
properties amongst which there was variation in a population, the raw material
on which natural selection operates, and through their reproductive behavior were
the source for the transmission of these traits across generations, and so important
entities for inheritance. It is true that in several often quoted passages, Darwin
also entertained the idea thatgroups of organisms could also serve these roles,
but it is clear that Darwin appealed primarily toindividual selection and only
rarely togroup selectionas the mechanism through which patterns of descent
with modification were established in the natural world.

2 FROM ORGANISMS TO GENES AND GROUPS

Such a view of natural selection was largely taken for granted by advocates of
Darwin’s theory until the Evolutionary Synthesis in the 1930s and 1940s. While

General editors: Dov M. Gabbay,
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Handbook of the Philosophy of Science. Philosophy of Biology

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