Darwin's Selection Analogies

Jonathan Hodge
History and Philosophy of Science, University of Leeds

Gregory Radick
History and Philosophy of Science, University of Leeds

Roger White
History and Philosophy of Science, University of Leeds

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     Last modified: February 25, 2005
     Presentation date: 07/14/2005 4:00 PM in ROZH 107
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Abstract
Despite extensive recent discussion, no consensus has emerged about Darwin’s selection analogies. We (two historians of biology and a philosophical analyst of analogy and metaphor) propose as a basis for consensus an integration of three uncontroversial claims : (i) any analogy was traditionally understood as a statement of proportionality (ii)Darwin conformed the overall argument of the ORIGIN to the vera causa ( true or real cause ) ideal (iii) Darwin’s analogical arguments for the ability of natural selection to produce, diversify and adapt species include a fortiori arguments. For brevity: the PROP, VC and AFclaims.

PROP shows when Darwin is comparing relations between relata and when he is comparing or contrasting the relata .A PROP fundamental to Darwin’s arguments states that natural selection is to wild species formation as artificial selection is to domestic race formation. That is NS:WSF::AS:DRF. ( Cf. 8:4 ::24:12).The relation between NS and WSF is the same as the relation between AS and DRF. This PROP does not as such assert any similarity between NS and AS (Cf. Sheep are to lambs as people are to children); this is so even though the analogy entails its alternation: NS:AS::WSF:DRF (Cf. 8:4::24:12 entails 8:24::4:12)

Darwin accordingly gives independent arguments for likening NS and AS. For his overall VC argument requires establishing that NS exists, that it is like AS but vastly more powerful. NS is like AS because in nature as on the farm there is hereditary variation due to changing conditions (although there is more variation on the farm ) and because ,thanks to the struggle for existence in the wild, there is selection of variation there too; and this natural selection being way more prolonged, comprehensive and discriminating is way more powerful than AS despite the lesser variation . Given that AS has produced, diversified and adapted to man’s ends DRs, then NS is capable of producing, diversifying and adapting species to circumstances in the wild .Here there is an appeal to a fortiori arguments : if AS has been able to do so much, then ,a fortiori, how much more will the vastly more powerful NS be able to do. Here, Darwin’s AF arguments conform to Biblical and other theological AF precedents, appropriately since for Darwin, at the time when he first formulated his analogies, nature was the art of God.

By integrating PROP, VC and AF issues, we get new light on (a) how Darwin’s thinking was transformed when ,late in 1838, he first came the analogy (b) how NS as a metaphor relates to NS as analogy (c) how such systematic analogical theorising in natural science compares and, even more, contrasts with less systematic analogies and metaphors in other genres of prose and poetry.