title: Testicular volume is inversely correlated with nurturing-related brain activity in human fathers.
abstract: Despite the well-documented benefits afforded the children of invested fathers in modern Western societies, some fathers choose not to invest in their children. Why do some men make this choice? Life History Theory offers an explanation for variation in parental investment by positing a trade-off between mating and parenting effort, which may explain some of the observed variance in human fathers' parenting behavior. We tested this hypothesis by measuring aspects of reproductive biology related to mating effort, as well as paternal nurturing behavior and the brain activity related to it. Both plasma testosterone levels and testes volume were independently inversely correlated with paternal caregiving. In response to viewing pictures of one's own child, activity in the ventral tegmental area--a key component of the mesolimbic dopamine reward and motivation system--predicted paternal caregiving and was negatively related to testes volume. Our results suggest that the biology of human males reflects a trade-off between mating effort and parenting effort, as indexed by testicular size and nurturing-related brain function, respectively.
authors.affiliation: Department of Anthropology and Center for Translational Social Neuroscience, Emory University, Atlanta, GA 30322.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Mascaro
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Hackett
authors.forename: James K
authors.initials: JK
authors.lastname: Rilling
mesh_terms: D000328:Adult; D001519:Behavior; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D002675:Child, Preschool; D005220:Fathers; D005260:Female; D006801:Humans; D007223:Infant; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D016487:Parenting; D013737:Testis / Q000033:anatomy & histology*; D055815:Young Adult
keywords: empathy; sperm competition
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