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Abstract Previous research on males, undergraduates and delinquents has shown that high mating effort is significantly correlated with delinquency, promiscuity and coercive sexual behaviour. Mating effort is defined in terms of the r/K trade-off with parental effort, such that persons at the r-end of the continuum seek to produce many offspring without great investment in their welfare, whereas the K-end of the continuum involves the production of fewer offspring and greater nurturing. A priority to gain and guard short-term mates potentially provides an evolutionary basis to offending. The Mating Effort Scale (MES) was administered to 564 (M:F 308:256; mean age = 14.1 years (SD 0.92)) unselected adolescents in mainstream education. Delinquency was measured using Moffitt’s Self-Report Early Delinquency Instrument (SRED). Results show that MES and the SRED correlated at r = 0.5 (p < 0.001), and at a similar magnitude for the SRED’s subscales. Even with the highly restricted range, age correlated positively with mating effort and delinquency. Correlations were found to be of equal magnitude in both males and females. These results suggest high mating effort in both sexes is strongly related to delinquency in a normal population confirming the putative use of concepts from evolutionary psychology to understand forensic issues.

1. Introduction The positive correlation between delinquent and criminal behaviour and mating effort in males has been established for some years (Ellis, 1988), and recently reaffirmed by Rowe, Vazsonyi, and Figueredo (1997) and Lalumière and Quinsey (1996). Mating effort is defined as “energy expenditure allocated to locating, courting, and sexually interacting with individuals of the preferred sex and age” (Lalumière & Quinsey, 1996, p. 34). Sexually interacting need not necessarily mean sexual intercourse, it may refer to any sexual contact. What Lalumière and Quinsey describe as mating effort can also be understood in terms of the r-end of the r/K continuum. Individuals towards the r-end of this continuum show rapid development of sexual functioning, non-bonded copulations, little effort in rearing their young and high fertility ( Ellis, 1988). Wilson and Daly (1985) studied homicide and other violent crimes in Detroit. One of the most striking aspects of their research was the apparently trivial reasons that young men gave for committing violent and often fatal acts. Examples included a murder resulting from a man being embarrassed and another murder that followed name calling in the street (p. 65). These acts of violence seem to stem from an individual feeling the need to save face in the light of an insult (be it perceived or actual). Wilson and Daly (1985) postulated that the reason so much violent crime is perpetrated by, and against, young males is because they are in competition with one another for resources. These resources include political influence, social status, access to material wealth, and females. In most human societies females are a contested resource and it is routinely seen that males who have achieved high status have more access to females. This has been demonstrated repeatedly through studies during the last 70 years which showed no change in the female preference for high status males (Buss, 1999, p. 106). At the other end of the continuum there are males who may suffer complete reproductive failure. Complete reproductive failure is the worst possible evolutionary outcome, so a male may engage in a variety of behaviours (however socially unacceptable) that he believes will reduce the likelihood of him experiencing this complete failure. These socially unacceptable behaviours may take the form of risky and/or violent competition, success in which may give reasonable prospects of improving status. Improved status results from successful risk taking often evoking admiration. It is assumed that those who succeed have some special quality which facilitated their success and which will ensure success in the future (Wilson & Daly, 1985). Those who fail in their risk taking may be expected to fail again and consequently lose status and face. The need to save face and improve status is thus established as a powerful motivator for reckless male behaviour. This motivation is considered by Bogaert and Rushton (1989). They examined the gene-based r/K theory as an approach to mating effort and delinquency. Essentially the r/K relationship represents the trade off between mating effort and parental effort. Extreme r represents maximum egg production and no parental care whereas extreme K represents minimum birth rate and maximum parental care. According to Bogaert and Rushton this relationship is responsible for many aspects of a person’s physiology and personality. “Individuals … higher in K, relative to those lower, should be larger in size, maturationally delayed, longer lived, intelligent, altruistic, sexually restrained, and come from smaller more stable families…” (p. 1017). Earlier research by Rushton (1987) found that women who produced dizygotic twins (greater egg production) experienced earlier menarche and menopause, more pregnancies and shorter menstrual cycles. The results of their study found that although the correlations between r/K factors and delinquency were small, they still existed in the directions predicted. It should be noted that Bogaert and Rushton (1989) used a sample of undergraduates for their study, thus reducing the intellectual and socio-economic variation that would be found in the general population. Writing at the same time, Ellis (1988) found seven universal correlates of crime which could be understood in terms of the r/K relationship. He suggested that those individuals who are closer to the r-end of the continuum are more likely to perpetrate “victimful criminal offences” as these acts are “manifestations of r-selection” (p. 699). The victimful offences of which Ellis writes typically involve detrimental effects on the victim’s reproductive fitness and positive effects on the perpetrator’s. Lalumière and Quinsey (1996) used undergraduates, to assess the correlation between mating effort and coercive sexual behaviours. Lalumière and Quinsey found self-identified coercive males had higher mating effort scores than non-coercive males. They also found that these coercive males had perceptual and cognitive biases such that they had “more difficulty reading female negative cues, and [were] more likely to attribute sexual desire to a rape victim” (p. 34). In addition to this, and pertinent to the current study, was the significant positive correlation between mating effort and antisocial behaviours which was found. Hunter, Figueredo, Malamuth, and Becker (2003) also found that mating effort was not only correlated with sexual offending, but also with non-sexual delinquency and other deviant behaviours in juvenile sex offenders. Weiss, Egan, and Figueredo (2004) found that (in undergraduates) mating effort correlated with an interest in sensational topics which are often associated with violent or criminal behaviour. These topics included guns, martial arts, pyrotechnics and the armed forces. There appears, therefore, to be a definite link between mating effort and delinquency and its associated risk taking, violence, promiscuity, and coercive sexual behaviour. These negative behaviours may be triggered by a perceived need to improve status, or a gene-based set of behaviours which individuals are unable to significantly alter. Whatever the mechanism for the behaviours, it is agreed that the results of high mating effort are often socially undesirable. Rowe et al. (1997) suggest an alternative perspective on the behaviours of high mating effort individuals, in which antisocial behaviour is an evolved adaptive strategy: “in this view, characteristics such as the lack of a conscience are not viewed as a deficit, but instead as an advantage in the context of an exploitative reproductive strategy” (p. 105). Egan and Angus (2004) show that both adult males and females with high mating effort are more likely to engage in extramarital affairs than those with low mating effort. Extramarital affairs require individuals willing to “betray another’s trust and intimacy” ( Egan & Angus, 2004, p. 584) which in this context is a reproductive advantage. Rowe et al. (1997) offer two possible evolutionary models for high mating effort. The first is the ‘conditional strategy’ where individuals may have genetically identical nervous system characteristics, but their responses may be environmentally contingent. The second is the ‘alternative strategy’ whereby pre-existing genetic variation causes varying behavioural dispositions among individuals. Taking the alternative strategy into consideration, some males would already be “genetically predisposed to strong mating effort tactics and delinquency, whereas others would be genetically resistant to the same behaviours” (Rowe et al., 1997, p. 107). This has implications for the idea of competitive disadvantage. Instead of competitive disadvantage being a result of delinquency it would be the predetermined outcome of a particular genetic combination. A perspective more like the conditional strategy is that of Quinsey (2002). He states in his review that general delinquent and antisocial behaviour which starts late and ceases early “appears to be a manifestation of mating effort and inter-male competition in response to competitive disadvantage” (p. 9). The research presented so far supports a model whereby antisocial, promiscuous, coercive behaviour occurs among males of varying ages with high mating effort. Although there is agreement on what mating effort is and its relationship with parental effort, there are mixed opinions regarding its relationship with other behaviours and its significance to crime. Previous research has concentrated almost exclusively on males with only incidental mention being given to females if they were included in the sample. Given that females have been considered the resource to compete for, and with greater fitness variance in males, it makes sense that research should have taken this direction. However, females have been found to display a similar relationship with mating effort and crime ( Rowe et al., 1997). Campbell (1995) also highlighted this lack of focus on females and the correlation over age between males and females for assault, which is 0.89 (p < 0.001). If the pattern of delinquent behaviour is so similar between the sexes, the question of it having the same underlying cause must be considered. Campbell (1995) argues exactly this, suggesting that the reproductive strategies of females can account for the majority of their violent behaviour towards each other and for other delinquent activity. Much of the research discussed (with the exception of Campbell) has been carried out on undergraduates who are selected for intelligence and tend to be socially homogenous. This study measures mating effort and delinquency in a large, representative sample of Scottish adolescents with a view to understanding the relationship in a diverse and younger adolescent population. It is predicted, based on existing research, that there will be a significant positive correlation between mating effort and self-reported delinquency, and that this correlation will exist for males and females.

3. Results 3.1. SRED Parallel analysis and factor analysis of the 58 items produced five factors with an eigen value ⩾1.7 (accounting for 45.2% variance). The five factor solution is shown in Table 1. The KMO for the SRED data was 0.94 indicating excellent suitability for factor analysis. Bartlett’s test of sphericity was significant at the p ⩽ 0.001 level indicating the data does not differ significantly from the multivariate normal. Comrey’s (1973) criterion for ‘fair’ loadings was used in the factor analysis and loadings below .4 were suppressed in the table for the sake of clarity. Table 1 shows the loadings for each factor in bold. Split loadings above .4 are loaded onto the factor for which they load the highest. Table 1. Factor analysis of the SRED (N = 564) Item Varimax rotation (16 iterations) F1 F2 F3 F4 F5 Carrying a weapon .68 Fighting in the street .66 Breaking windows of empty building .66 Using a weapon .64 Hitting a person to hurt them .64 Getting suspended/expelled .56 .43 Throwing objects at people/cars .52 Going around in a group .52 Struggling with police officer .52 Damaging a parked car .44 Raising a false alarm .43 Gambling .41 .41 Letting down tyres .40 Getting drunk .78 Buying or drinking alcohol .77 Trouble through alcohol .60 Graffiti in public place .57 Truancy .56 Stealing alcohol .55 Smoking cannabis .46 .53 Drinking alcohol at school .49 Damaging public property .49 Trespassing .63 Going to see 15/18 rated films .59 Prank telephone calls .58 Swearing loudly in public .44 .51 Starting a fire .50 Fare dodging .40 .48 Stealing between 50 p and £10 .73 Stealing less than 50 p .65 Shoplifting .62 Stealing over £10 .55 Taking a car without permission .74 Breaking into a house .62 Stealing out of a parked car .61 Driving without a licence .50 Stealing a bicycle .48 Table options The five factors identified were labelled according to the nature of the items they contained. Factor 1 was labelled ‘Antisocial’ as it contained items of a generally disruptive or rule-breaking nature. Factor 2 was labelled ‘Alcohol and Vandalism’ (AlcVan) as the majority of items related to the consumption or acquisition of alcohol and the destruction or damage of public property. Factor 3 was named ‘Transgressive’ as some of the items were illegal acts whereas others related to less serious misbehaviour. Factor 4 was straightforward to label as all of the items related to theft. Finally, factor 5 was labelled ‘Criminal’ as all of the items involved breaking the law in a significant way e.g. breaking into a house. Reliability analysis of the five factors indicated acceptable to excellent alpha values: F1 = .9; F2 = .9; F3 = .8; F4 = .8; and F5 = .7. Independent samples t-tests showed that males scored higher than females on all but one of the delinquency factors. There was no significant difference between males and females on the alcohol and vandalism factor (see Table 2 for summary of the gender comparisons). Table 2. Gender comparisons Variable Mean (SD) df t Female Male Mating effort −2.05 (6.76) .48 (6.79) 523 −4.25⁎⁎ Antisocial 3.20 (4.62) 7.03 (6.5) 530 −7.62⁎⁎ AlcVan 5.12 (5.09) 5.53 (5.27) 517 −.901 Transgressive 5.09 (3.47) 6.75 (3.77) 517 −5.22⁎⁎ Theft 1.67 (2.03) 2.24 (2.39) 526 −2.93⁎⁎ Criminal .25 (.89) .82 (1.56) 541 −5.12⁎⁎ ⁎⁎ Difference is significant at the 0.001 level. Table options 3.2. MES Mating effort was measured on a −2 to +2 scale giving a range of scores from −20 to +20. Males scored significantly higher than females (t = −4.25, df = 523, p < 0.001) as predicted, and mating effort was also correlated with age. Analysis of skewness and kurtosis revealed the data for the MES had excellent psychometric properties ( George & Mallery, 2003). 3.3. Correlations A correlation matrix was generated to test the main hypothesis that mating effort and delinquency would be positively correlated. Table 3 shows the positive and significant relationships between the variables generated through factor analysis of the SRED, and mating effort score. There was also a positive correlation with age and delinquency as predicted. Table 3. Correlation matrix of measures (N = 564) MES Age Theft Antisocial AlcVan Transgress Criminal MES 1.00 .13⁎⁎ .32⁎⁎ .50⁎⁎ .44⁎⁎ .44⁎⁎ .28⁎⁎ Age 1.00 .16⁎⁎ .24⁎⁎ .41⁎⁎ .36⁎⁎ .12⁎⁎ SREDTheft 1.00 .50⁎⁎ .52⁎⁎ .53⁎⁎ .34⁎⁎ SREDAntisocial 1.00 .66⁎⁎ .65⁎⁎ .60⁎⁎ SREDAlcVan 1.00 .65⁎⁎ .40⁎⁎ SREDTransgress 1.00 .39⁎⁎ SREDCriminal 1.00 ⁎⁎ Correlation significant at the 0.001 level (two-tailed). Figures in bold demonstrate the relationship between the five factors of the SRED. Table options 3.4. Gender comparisons Given the clear differences in gender between scores on mating effort and delinquency, correlations for males and females were compared to see if the positive, significant relationship between delinquency and mating effort was as strong for both sexes. Fisher Z-transformations of the correlates show that the relationship between the two variables does not significantly differ between males and females, suggesting that a participant’s mating effort is a good predictor of their delinquent behaviour regardless of gender (see Table 4). Table 4. Correlation with mating effort and comparison across sex Male Female Fisher Z Antisocial .46 ⁎⁎ .49⁎⁎ .681 n.s AlcVan .44⁎⁎ .44⁎⁎ .93 n.s Transgressive .36⁎⁎ .48⁎⁎ .103 n.s Theft .29⁎⁎ .31⁎⁎ .846 n.s Criminal .25⁎⁎ .27⁎⁎ .821 n.s n.s. = not significant. ⁎⁎ Correlation significant at the 0.001 level (two-tailed)