that this proposition is plausible. For example, testosterone is lower in fathers as compared to non-fathers, and preliminary evidence suggests that men may be able to discern cues of fertility in women. The support for the challenge hypothesis in non-human animals provides a foundation for which to explore the relationship between testosterone and aggression in humans. The Dual Hormone Hypothesis as an Extension of the Challenge Hypothesis The challenge hypothesis claims that there is an association between testosterone and aggression in mating contexts, and more broadly status-seeking behaviours. However, findings linking testosterone to status-seeking behaviours, especially in humans, are often inconsistent and leave room for critique. In some cases, testosterone has been seen to positively correlate with status-seeking behaviours such as aggression and competitiveness, however, testosterone has also been found to have weak or even null correlations with the same behaviours. Some scholars blame these inconsistencies on limitations in study methods, but the dual-hormone hypothesis has emerged as a theoretical explanation to some of these inconsistencies. Dual-Hormone Hypothesis Stress plays a fundamental role in competition and mating, and therefore, the hormones released in response to stress should be considered as well as testosterone when looking at the challenge hypothesis. Cortisol is produced in the hypothalamic-pituitary-adrenal gland and is released when one is under physical or psychological stress; this is relevant to the challenge hypothesis as testosterone-linked status-seeking interactions are often stressful situations. According to the dual-hormone hypothesis, the correlation between testosterone levels and aggression/status-seeking behaviour is reliant on corresponding cortisol levels; there is a strong correlation between the two when cortisol levels are low, and a weaker or sometimes reversed correlation when cortisol levels are high. There is supporting evidence for this relationship from a study done on humans, which looked at social status, leadership, and aggression. Cortisol is seen as a moderator of the relationship between testosterone and status-seeking/reproductive aggression in this hypothesis. However, the dual-hormone hypothesis also has its own flaws, and current evidence appears to only partially support the hypothesis, according to a meta-analytical evaluation in 2019 by Dekkers et al. A proposed reasoning for the occasional weak evidence is that cortisol and testosterone, further interact with social context and individual psychology to regulate status-seeking behaviours. One such context is ‘victory-defeat’, where testosterone and cortisol will interact to increase desire to compete again more after losing than winning, as a method of regaining social status. Individual personality