Fig. 1.

Relationship between reproductive biology and paternal investment. (A) Caregiving vs. testes volume residuals after testes volume was regressed against height. The dotted line indicates the score (72) at which mothers and fathers are equally responsible for their child’s daily care. Scores below 72 imply that the mother does more than the father and scores above 72 imply the opposite. (B) Caregiving vs. plasma testosterone levels. (C) Plasma testosterone levels vs. testes volume residuals (regressed against height).