Essential differences between Darwinism and neo-Darwinism

Andre Ariew
University of Rhode Island

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     Last modified: February 15, 2005
     Presentation date: 07/15/2005 9:00 AM in MACK 237
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Abstract
Part of Double Session: "Population Thinking"

A central feature of Darwin's natural selection is that it explains exquisite adaptations by citing conditions that determine whether a variant will become prevalent in a population. In shorthand, natural selection explains adaptation by explaining trait spread. Two additional features of Darwin's theory are its generality or near universality (setting inheritance of acquired characteristics and sexual selection to one side), and that it is a causal/mechanical theory. By "causal" I mean, in short, natural selection answers the question 'what about this heritable variant allows it to spread in the population' by referring to the relation between the natural properties of individual bearers that possess the trait and their local environmental conditions. Consequently, natural selection is able to explain adaptation because it is causal.

On the conventional story about neo-Darwinism, Darwin's theory is redescribed in statistical terms and imbued with a genetical theory of inheritance. All of the central features of natural selection are preserved in this modification: A. it explains both spread and adaptation, B. it is general, C. it is causal. The genetical/statistical theory is Darwinism reborn.

I take issue with this conventional story. First, B. is inconsistent with C. The question what about a heritable trait allows it to spread may have nothing to do with the natural properties of its bearers. It may, for instance, have to do with the structure or dynamics of the population for which it is a member. To maintain generality neo-Darwinian theory tracks population dynamics; it models how traits spread. They dynamics do not underwrite a particular theory about the causes of spread. Consequently, neo-Darwinian theory, as opposed to Darwin's theory, decouples an explanation of spread from a theory of adaptation. As far as we are concerned with the features A-C, the genetical/statistical theory is not Darwinian.

Multiple Paper Session:
Other papers in this session:
Population Thinking: A Typology
Taking intra-generational success seriously for our understanding of fitness
Population Structure
Population Thinking and Virtue Ethics