This was written in 1993 because of a requirement to address the circularity issue. It is reproduced here for what it adds to a companion essay and what they together say about the importance of variation vis a vis selection over evolutionary history.
For the purposes of this essay, we will consider not the hackneyed phrase familiarly identified with evolutionary selection since Darwin, but rather a phrase which may well have been equivalent had it instead had that century plus of familiar use. It is not our task here to make a linguistic case for the purported equivalence of the two phrases, but rather to employ their hypothetical equivalence as a premise from which to commence to deconstruct the populist theory of selection and its pervasive influence on western culture.
Selection theory is an attempt to ascribe the fact of evolutionary history to local cause and effect mechanisms. To account for the historical fact of continuance of lineages, the theory requires individual organisms to have a tendency to maintain their identities over sufficient time for some of them to undertake, within their species, one or more reproductive acts of sufficient fecundity. (Accounting for the related facts of adaptation and division of lineages is the task of a separate essay.) This essay is particularly concerned that reproductive acts generally require collaboration between individuals and often between species—collaborative acts that are more obvious though possibly no more important than those involved in simply staying alive.
Had it been used, as it might well have, late last century to describe a tendency to reproductive success, 'sexy' may have established connotations beyond its still essential but entirely superficial characterisations of today. Deeper sexiness would include the ability to stay alive long enough to have a chance to reproduce as well as behaviours eliciting collaboration. Caterpillars and honey bee workers could have an agreed sexiness metric from which their contribution to the prosperity of genotypes could be derived; at least in the ecological isolation of a genetics laboratory.
In order to reject accusations as to the circularity of a theory of the prosperity of the sexiest, it is necessary to establish independent measures of prosperity and sexiness, to show an historic correlation between these measures, and to show significant success in predicting future prosperity from measured sexiness. A sexiness metric could only sensibly be applied to phenotypes. On the other hand, a metric for prosperity could at least theoretically be ascribed to individual genes. While validation of estimates of future prosperity based on outcomes of biological evolution is fraught with methodological obstacles, within the often analogous domain of social evolution, consumer marketing is one obvious area in which such a theory is assumed to be both historically valid and predictive.
A counterpoint, seemingly supporting the circularity claim is that our highly evolved perception of sexiness may be an unavoidable adaptation through a long history of interaction with the prosperous and potentially prosperous. Any capability to anticipate prosperity should have selective advantage, so perception of the prosperity metric may be disguised as sexiness for reasons of cognitive dynamics—analogous to the claimed rationale for adaptive self deception as to the sources of morality. From another angle, a bee's view of a flower could be ascribed as identifying the flower's sexiness (in the broad sense), although the reciprocal of such a claim would certainly be obscure. No matter by what means it is perceived, sexiness will be a rating for individual entities which does not biologically accumulate or distribute in the way that is implicit for any metric of prosperity.
In developing a metric for sexiness, the easy bit is to temporally equate it to expected fecundity, that is the likelihood of an individual getting productive sex. The hard question is to define the most appropriate temporal extent over which the productivity of a sex act is assessed, from, at one extreme, the instant of gratification to, at the other, the generation cycle from one such act to the same point in the life of a child resulting from the first act, or even a little further to account for any 'sexy grandmother' factor. It is reasonable to predict that increasing the time considered would at least marginally increase the correlation with prosperity, but that such a gain might be incurred only at a much higher cost in making such measurements over extended time.
Numerous species of fishes and marine invertebrates disperse their fertilised zygotes to the mercy of the currents as planktonic larvae, while closely related species may care for their young during early development. Species with planktonic larvae necessarily extend over a broad geographic range and have a 'conservative' genotype, while those making an ongoing investment to their young are able to undergo rapid adaption and local speciation. For the former, it would make no sense to ascribe any component of sexiness beyond the point of zygote dispersal, but for the latter and for non-cuckoid birds and mammals, productive parenting could well be considered a legitimate component of deeper sexiness.
Now how can we measure the prosperity of a gene or of a species? Simplistic answers such as biomass and entropy dissipation are heavily biased in favour of those forms which accumulate cellulose, analogous to the simplistic measure of social prosperity provided by decorated rectangles of reprocessed cellulose. Measurement of cellulose is easy, but measurement of more anthropophilic indicators of prosperity presents significant challenges. An ecological metric of prosperity would account for the value of complex webs of collaboration from sexual reproduction to human society.
Complex systems form to dissipate some kind of energy flux. Civilisation has seen the flux of human sexiness pushed to ever higher levels through social proscriptions and the contemporous invention of complex social forms for dissipation of that sexiness flux. Complex systems are also vulnerable to collapse when sufficiently stressed, be it by an asteroid impact or other totalising regime. Importantly, the very notion of optimality which is generally treated as implicit in selection for sexiness cannot lead to a monopoly on prosperity. The historical fact of evolution is of a succession of viable species becoming increasingly prosperous through extended webs of interdependence. In the dynamics of complexification, optimal equals static equals dead(end).
In conclusion, it can be seen that sexiness is an important factor in determining prosperity. Holding other factors constant, sexiness can be shown to be a proximate cause of prosperity and will therefore be selected in such circumstances. However, it is not the only cause—the important contribution of innovative capacity over many generations being the subject of a related essay. The fact that sexiness is an evolved characteristic of phenotypes does not make prosperity of the sexiest a circular argument. History shows increasing diversity of life over time which would not be the case if prosperity was an efficient cause of sexiness, and locally or temporally decreasing diversity seriously degrades ecological prosperity in clear denial of the circularity claim.