Fig. 1.

Males classified as escalating aggressive had lower levels of circulating steroids than stable aggressive types. Circulating steroid hormones titers after the dyad show males in the escalating aggression category had lower levels of estradiol, cortisol, testosterone but not 11-ketotestosterone. Data are plotted as concentration (ng/ml). Top and bottom of boxes represent the first and third quartiles, respectively; whiskers extend to the most extreme data points no more than 1.5 times the interquartile range from the box; and horizontal lines within the boxes represent group medians. Asterisks indicate a statistically significant difference (*P<0.05, Mann–Whitney).