Fitness: Philosophical Problems


Fitness plays many roles throughout evolutionary theory, from a measure of populations in the wild to a central element in abstract theoretical presentations of natural selection. It has thus been the subject of an extensive philosophical literature, which has primarily centred on the way to understand the relationship between fitness values and reproductive outcomes. If fitness is a probabilistic or statistical quantity, how is it to be defined in general theoretical contexts? How can it be measured? Can a single conceptual model for fitness be offered that applies to all biological cases, or must fitness measures be caseā€specific? Philosophers have explored these questions over the last several decades, largely in the context of an influential definition of fitness proposed in the late 1970s: the propensity interpretation. This interpretation as first described undeniably suffers from significant difficulties, and debate regarding the tenability of amendments and alternatives to it remains unsettled.

Key Concepts:

  • Actual offspring production is an unsuitable definition of fitness.

  • The propensity interpretation of fitness was proposed as a way to base fitness on expected, rather than actual, offspring production.

  • The propensity interpretation is problematic, as it makes fitness difficult to measure, relies centrally on the arithmetic mean and fails to take into account local environmental factors.

  • Some philosophers have rejected the propensity interpretation in favour of an ecological fitness concept or a purely statistical fitness concept.

  • Others have attempted to modify the propensity interpretation in order to resolve its problems.

  • The debate over which of these concepts of fitness best solves the philosophical problems at hand remains unsettled.

Keywords: environment; evolution; fitness; drift; measurement; natural selection; propensity interpretation; tautology


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Ramsey, Grant, and Pence, Charles H(Jun 2013) Fitness: Philosophical Problems. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0003443.pub2]