They suggest that this is because high testosterone is related to a "competitive-type relationship orientation" (van Anders et al., 2007) in men who have a greater propensity to enter new relationships. A reduction in testosterone will facilitate men who have a reduced investment in mating effort (such as pair-bonded men and/or fathers) to subsequently increase their inclusive fitness by alternative means, such as relationship maintenance and caring for offspring (Gray et al., 2002; Wingfield, Hegner, Dufty, and Ball, 1990). Using a median split analysis, participants who indicated that they had been in their relationship for less than 12 months were categorized as being in "new relationships" and those in longer relationships being categorized as in long-term relationships. The findings revealed men who received the testosterone gel were more honest when they self-reported their numbers. In a study published in PLoS ONE, men were either given testosterone gel or a placebo, and asked to roll the dice in private, report the numbers they landed on, and receive money based on the outcome. Surprisingly, testosterone can foster social behavior; specifically it can make men more honest. They were able to select multiple options and indicate "other" to describe their relationship status further. There also may be a connection between relationships and your testosterone levels. Furthermore, even though there was found to be significant differences between the different relationship types, no significant correlation was found between relationship length and levels of testosterone (however, it is worth noting from Figure 1 and the reported correlation size that this may be partly due to the sample size). This perhaps reflects that the internal psychological mechanism that mediates changes in the levels of testosterone in men in relationships is a complex one, and difficult to measure when using external indicators of "commitment" (be it marriage, fatherhood, or length and/or type of relationship). Similarly the negative effect that age can have on testosterone levels (e.g., Harman, Metter, Tobin, Pearson, and Blackman, 2001) is also not responsible for these differences, as there was no significant difference between the ages of participants in the different relationship categories. This suggests that the psychological change in motivation to compete (and with it, the subsequent drop in levels of testosterone) tends not to have occurred for those in new relationships. When your testosterone—the key male sex hormone produced by the testicles—is low, it brings with it symptoms like fatigue, a depressed mood, erectile dysfunction, and low libido—all things that can affect relationships. Future research can draw on these findings and progress our understanding further, for example by employing longitudinal methods to assess changes in levels of testosterone as men go through these different life transitions. Our contribution adds to this by showing that being in the early stages of a relationship is an additional variable that can be used to assess varying levels of testosterone in men. Our understanding of how a man's levels of testosterone changes over the course of a relationship is a good example of how research can successfully investigate evolutionary-based hypotheses of human behaviour. A potential limitation of this study is the median split of 12 months for "new relationships." This is acknowledged, but should not undermine the findings as it has acted as a reliable comparison in our analysis. To control for the potential influence of participants' extra-pair sexual interest, the original ANOVA was also repeated with participants' previous extra-pair sexual activity ("had engaged" vs "had never engaged") as an additional between-subjects measure. There were no further significant correlations between levels of testosterone and any other indicators of relationship quality, including relationship length (see Figure 1). This was measured using the original 7-item Sociosexual Orientation Inventory (SOI) devised by Simpson and Gangestad (1991). They were then asked how often they saw their partner each week ("Every day," "Every other day," "1–3 times a week," "Less than once a week") and the last time they saw them ("Today," "Yesterday," "Within the last five days," "More than a week ago"). A total of 76 heterosexual male university students from the north east of England, aged between 18 and 39, took part in the experiment. In other words, they do not show the same hormonal response to external cues (such as marriage or fatherhood) as have men who are "honestly" committed to reduced mating effort. These findings support the first study hypothesis, as long-term paired men had lower levels of testosterone than both single men and men in "new relationships." Furthermore, there was no significant difference in the levels of testosterone between men in new relationships or single men. Examples of this include the findings from multiple studies that pair-bonded men (who are either married or in long-term, committed relationships) have lower levels of testosterone than single men (Booth and Dabbs, 1993; Burnham et al., 2003; Gray, Chapman, et al., 2004; Gray, Kahlenberg, Barrett, Lipson, and Ellison, 2002; Mazur and Michalek, 1998; van Anders and Watson, 2006). Also, neither sociosexual orientation measures (SOI-behavior and SOI-attitude) nor interest in extra-pair sexual activity had a significant influence on the difference in levels of testosterone between the different relationship categories, nor did they have a significant effect on levels of testosterone overall. To examine the relationships between levels of testosterone and sociosexual orientation, Pearson's r correlations were conducted on levels of testosterone, age, scores for the two factors of SOI (SOI-behavior and SOI-attitude), and overall SOI score for all participants. We also conducted an analysis to examine if additional measures of sociosexual orientation and interest in extra-pair sexual activity affected how levels of testosterone vary between the different relationship types.