在一项研究了交配和抚养之间可能存在的权衡关系的研究中，科研人员发现，与其他男性相比，睾丸尺寸较小的男性更有可能参与对孩子的抚养。一项叫做生命史理论的进化论假说认为，交配与抚养会争夺动物用于繁殖而付出的有限的能量。此前的研究已经提出，睾酮的减少可能会抑制为交配做出的努力，这可能会把资源导向对新生儿的抚养上。考虑到睾丸体积与精子制造以及睾酮水平有联系，James Rilling及其同事研究了睾丸尺寸和男性参与抚养孩子之间的联系。这组作者招募了亚特兰大及其周边的70名21岁到43岁的生育有1到2岁子女的父亲，然后使用磁共振成像（MRI）测量了这些男性的睾丸体积，并且在这些男性观看他们自己的孩子、陌生人的孩子或者一名成年陌生人的时候测量了大脑参与父母动机的一个区域的活动。这些男性的伴侣也回答了一个关于抚养的问卷调查，该调查询问了父亲对诸如带孩子去医院和夜间照料孩子等任务的参与情况。这组作者报告说，父亲的睾丸尺寸与他们观看自己孩子的照片时触发的与抚养有关的大脑活动存在着负相关的联系。尤其是对子女的有表情的面部做出更大反应的父亲倾向于有较小的睾丸，并且会更多地参与新生儿护理。这组作者说，睾丸尺寸与抚养相关大脑活动之间的这种联系提示了在交配和抚养之间的一种权衡的关系。（生物谷 Bioon.com）
生物谷推荐的英文摘要
PNAS doi: 10.1073/pnas.1305579110
Testicular volume is inversely correlated with nurturing-related brain activity in human fathers
Jennifer S. Mascaro, Patrick D. Hackett, and James K. Rilling
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.
