Digit ratio doesn't follow Rushton's rule

Chris Brand reviews a new book:
BOOK REVIEW of Manning, J. ( 2008), The Finger Book: Sex, Behaviour and Disease Revealed in the Fingers. Pp. 170 + xiii. London : Faber & Faber.

Reviewed by CHRIS BRAND. Available at Amazon

This book, by a British evolutionary psychologist at the University of Central Lancashire (formerly Preston Polytechnic), argues that there are links between ring-finger length (RFL), testosteronization in the womb, masculinity, personality, polygamy and race. It gets off to a slow start, but there is drama enough by the finish.

The ring finger is hairier in males than other digits, perhaps reflecting its being more under the influence of the sex hormone testosterone and its being assigned for the wedding ring. In any case, RFL, relative to index-finger length (the normal ratio in Whites is approximately 1:1), is greater in males and also in top athletes and sportsmen, autists, attention-deficit children and butch lesbians; and it correlates negatively with psychologists’ measures of agreeability, gentleness and femininity. Thus goes the first 90% of Manning’s (rather repetitive) book.

Of course there are some problems. It is not obvious why RFL should be measured from the point of the finger’s lowest skin crease with the palm rather than from the knuckle. The inter-observer reliability for RFL is not stated or even considered. There seems no special reason why testosterone should especially affect the growth of the ring finger. All the associations with RFL mentioned above are pretty slight (Manning does not give correlations but his occasional scattergrams indicate effect sizes of around .25). And other efforts to argue for links to RFL don’t really work at all: the promised link to left-handedness doesn’t materialize (though Manning might have tried ‘mixed-handedness’, often associated with mild personality difficulties), and the proposed link to schizophrenia is a mess (with too many complications arising from ‘testosterone inhibitors’ and genes determining the uptake of said inhibitors). But Manning has had no difficulty finding academic collaborators to undertake empirical work with him over the 15 years since the RFL links were first advertised to psychologists by Hans Eysenck’s ‘first lieutenant,’ Glenn Wilson; and there clearly is a case to answer.

[. . .]

All but the most piously anti-racist readers who have got this far with the present review will know of the claims of Philippe Rushton, Richard Lynn and the London School that the main established psychological gradation between the human races is that running from East Asians through Caucasians to Negroes and characterized primarily as one of inherited general intelligence (cf. IQ) though also being linked to law-abidingness and sexual restraint. Well, Manning likewise has a broad dimensional claim to outline – set out finally in a graph on the penultimate page of his book.

Though not especially motivated to study race – and thus apparently never having read any London School work – the empirical studies which he has found or organized have yielded a clear and interesting picture, bringing together Blacks and East Asians (Zulus, Jamaicans, Chinese and Japanese) as high-RFL and distinguishing them from the typically low-RFL Europeans (Polish, Spanish, English and Hungarian – with Germans and Gypsies scoring a little higher, intermediate with Chinese levels). For just what this means (if it replicates), Manning’s readers are left to refer to the book’s earlier claims. But the finding of a marked and allegedly important similarity between Blacks and East Asians will amaze many – and not just Rushton and Lynn. This is particularly because, having started his book by tending to play up the advantages of early testosterone (good for the heart, supposedly), Manning ends by making the human shift to right-handedness (long called ‘the right-shift factor’ by the equally unmentioned Marian Annette) fundamental to language and civilization as we know it and attributing it to foetal oestrogen and thus linking it to short RFL.

I've previously demonstrated black-white differences in circulating testosterone are minimal in adult males.

It's certainly conceivable there are racial differences in pre-natal androgen exposure, though--considering the major races are known to vary in any number of anthropometic indices not putatively linked to androgen exposure--it's not clear to me how meaningful unadjusted cross-racial comparisons of digit ratio are. Regardless, digit ratio can't be dragged out by those trying to shore up "Rushton's rule" with respect to androgenization.

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