Miller's hypothesised greater role for sexual selection in human cognitive evolution is welcomed, but we suggest that it has two limitations. First, omitting consideration of intra-sex competition, and of necessary constraints on creativity. Second, Miller's empirical focus is restricted to obviously creative products, rather than on more fundamental cognitive processes. We suggest that addressing the first limitation leads to empirical implications that address the second. We note some of the findings of our recent research in this area.
2. Miller's key argument is that sexual selection and the resultant challenges produced for mate selection has had profound effects on cognitive evolution for both sexes. Although many studies of animal mate selection have focused on the physical attributes that species' use to display and to select mates, Miller generalises this focus to cognitive display attributes. The role of physical display signals has been demonstrated in species as diverse as peacocks to humans, with the bright plumage of a peacock's tail and the size and muscle-tone of a man's chest both acting as basic signals of genetic fitness and high potential as a mate. Miller's precis, comments on the current limitations of both natural and sexual selection. Many species of animal display using attributes that have a cognitive basis and whose evolution has been affected by sexual selection. An example being in many species of birds, in which the males have developed increased sizes of hypothalamus to cope with the required song repertoire for effective display.
3.Thus argues Miller, the use of cognitive attributes as signals of high mate potential, ought to be emphasised. Skills that might appear to have limited evolutionary importance, such as art, humour and creativity actually play an essential role in mate choice and sexual selection acting as cognitive fitness indicators. Miller (1997) has argued that intelligence is an indication of an individual's ability to problem-solve - essential for effective survival. Hence the use of intelligence in display could act as indicators of the high mate value. Problem-solving intelligence would have both short and long-term benefits: short-term benefits during that male's life; and long-term, in the potential continuation of any genetically predisposed component of their intelligence.
4. An equally important aspect of the thesis is that females must have evolved converse receptivities to these displays: a particular liking for novelty or neophilia. This would reinforce males' use of creativity in display, providing the foundation for a runaway selection of the trait of novelty-production within males.
5. We suggest that the basis of Miller's argument is plausible(although he does not provide any new evidence to support his thesis -largely relying on evolutionary logic, and previous research). However, some elements are under-emphasised which may result in a somewhat different picture of how sexual selection might have impacted on cognition. Miller has under-emphasised the role of constraints on the productive mechanisms of creativity in male display. Second, he has not paid sufficient attention to the complementary receptive neophilia in females. Both of these limitations may result in part from the necessary lack of detail in such a wide ranging book as Miller's, potentially to be developed in further work. However, they become more important in the context of the book's other under-emphases, concerning the key roles of group-living and intra-sex factors in sexual selection.
6. Group influences are an essential aspect of human mating psychology, as Social Psychology demonstrates, and well-supported by recent research by Dunbar et al (see Dunbar, 1996). They found differences in male-group conversation topics depending upon whether females were present. In male only groups, conversation was based on ephemeral topical items, for example sport, women and material goods. However, they found that when women were present, male conversation shifted to more intellectual topics, such as politics, business and finance.
7. Considering creativity in male display first, Miller supports his hypothesis with examples from the world of arts, ornamentation and proteanism (random behaviour). Although the latter is linked most specifically to survival in individuals via predator avoidance capacities, Miller suggests that a protean mechanism might also underpin cognitive creativity. Miller supports creativity's sexual selection in males with the converse female neophilia. This allows a runaway selection of novelty production.
8. However, successful display products require constraints on creative production. Firstly, there are "product-typical constraints" - the novel product must be recognisable as a member of its category (e.g., recognisable as a joke), and as a display (i.e., it must be encodable as a reason for being attracted to the male). For many aspects of human communication and cognition, females must be aware that the product is actually intended as a display for it to be recognisable as a display. (cf., Relevance Theory).
9. Secondly, there are "species-typical constraints" - any display must be recognisable as display behaviour within that species. Miller employs Ryan's Sensory Exploitation Theory: species-specific perceptual biases within females shape the display of males via the sensory modes of display successfully recognised by females. Furthermore, a female may have several males displaying(either sequentially or concurrently) and will need to compare their displays. Those displays outside the species-specific parameters would be in danger of being rejected since their display is simply incomparable and unrecognisable as a display.
10. Miller's posited adaptive mechanism of neophilia is apparently not subject to any constraints. The hypothesis is that novelty is attractive due to its indications of intelligence leaving females possibly attracted to anything outside their species' display behaviour. Arguably not an adaptive strategy since madness can be associated with extremes of creativity but is not necessarily indicative of a good mate. Similarly, extra-species males, using similar sensory bases for display, would become attractive
11. Female comparison of male displays introduces the lack of emphasis on inter-male competition in sexual selection. Kodric-Brown & Brown (1984) have argued that inter-male competition is an important influence on sexually selection. Resources, display opportunities and access to females are essential to male mating success. Competition for these can be high and a male successful in intra-sex competition, has an increased chance of success in inter-sex display. This has both short and long-term ramifications: males successful in intra-male competition have increased opportunities of and likelihood of success in display, with better resources to offer to the female, and thus a wider, higher-value range of females to whom to display. In the long-term, a male who has attributes endowing success in intra-sex competition has an increased likelihood of passing these on within his genetic material.
12. Thus far, we have focused on theoretical aspects of Miller's book. Theoretical assessment links to an empirical assessment to which we now turn. In order to test Miller's hypotheses, reliable and standardised ways of considering creative production and assessment in higher cognition need to be developed. Miller's examples come from general, mainly art-based domains. Although these domains might be readily identifiable as creative, they lack a standardised measure. Since Miller's thesis is intended to have general consequences for cognition, rather than just obviously creative activities such as painting, it is necessary to go beyond prima facie creative domains into more mundane cognition. Only in this way can the generality of the thesis be assessed.
13. Key issues which would otherwise remain untestable include: the strength of the effects of sexual selection on creativity (e.g., what are the relative contributions of display to females as compared to competition between males?); explanations as to the presence and role of creativity in females; and whether, as a sexually selected adaptation creativity has had an impact on fundamental aspects of cognition, or "merely" on the operation of more obviously "artistic" skills; how extensive intra-female competition is and its potential effects on evolution and display; and, whether the operation of any such mechanism is context-dependent or context-invariant. To consider these and other issues, research needs to be developed within a testable area.
14. One area of "higher" cognition that may facilitate empirical evaluation of some of these issues, relates to the representation of concepts. As elements of thought and communication, concepts' properties of productivity and generality support their use in novel productions. Previous research on concepts and concept combinations in research on novelty production and assessment has shown this (Gerrig & Murphy, 1992). Following this, research is currently being carried out considering Miller's hypotheses, using concept combinations. The research considers the creativity of participants' interpretations of novel concept combinations. Experimental conditions produced either a stimulus for males to display (to a female) or to compete (with another male). Immediate results support Miller's findings, with the additional limits for which we have argued above.
15. Considering some of the implications of this research for Miller's hypotheses, we find that as predicted constraint occurs in the production by males and appreciation by females, of novelty. Analysis of explanations has shown that, overall, males were more 'creative' than females' (using type of interpretation as a standardised quantification, Gagni, 2000). However, in terms of content, the range of explanations was limited. Males had constrained the contents of their explanations. This meant that their explanations were appreciable and understandable as explanations of the target phrase rather than being completely creative or protean (only 6.2% of all responses were considered unconstrained). Preliminary analysis on female assessment of the males' explanations produced also supports the idea of constrained neophilia - a liking for interpretations independently assessed as creative but constrained.
16. Competition was also considered. In the control, there was no significant difference between male and female creativity. However, when motivated to both display or compete, males produced more creative explanations than females. Again, this supports our predictions. Additionally, analysis of the effect sizes between display and competition conditions suggests that when displaying males are motivated to be more creative than when competing. Further research is considering this finding.
17. Overall, we are very supportive of Miller's hypotheses. Effective, engagingly written, interesting and providing the foundations for important angles of research, Miller has produced a culmination of core ideas and research. Now additional research needs to commence, taking up some of these unfinished issues and unresolved questions; to continue furthering our understanding of evolution and cognition.
Dunbar, R.I.M (1996). Grooming, Gossip and the Evolution of Language. Faber and Harvard University Press.
Gagni, C. L. (2000). Relation-based combinations versus property-based combinations: A test of the CARIN theory and dual-process theory of conceptual combination. Journal of Memory and Language, 42, 365-389.
Gerrig,R.J & Murphy,G.L. (1992) Contextual Influences on the Comprehension of Complex Concepts. Language and Cognitive Processes Vol 7. Pp205-230.
Kodric-Brown, A & Brown, J.H. (1984) Truth in Advertising: the kind of traits favoured by sexual selection. American Naturalist vol 124 pp309-323.
Miller,G.F. (1997a) Protean Primates: the evolution of adaptive unpredictability in competition and courtship. In A.Whiten & R.W.Byrne (eds) Machiavellian Intelligence II: extensions and evaluations. Cambs: UP.
Miller,G.F. (2000) The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature. Heinemann
Miller,G.F. (2001) Precis of: The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature. PSYCOLOQUY 12(008) ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/2001.volume.12/ psyc.01.12.008.mating-mind.1.miller http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?12.008