Environmental epigenetics is the study of how environmental signals affect gene expression. Within this growing field of molecular biology, experiments on the epigenetic effects of 'maternal care' on offspring health have received much scientific and public attention and are often called upon to showcase how environmental epigenetics will create a new understanding of life as inherently 'biosocial.' While, on the one hand, this research is exciting and offers possible opportunities for collaboration between molecular biology and the social sciences, it is also necessary to consider its political dimensions. In this paper, we show how commonsense assumptions about sex, gender, sexuality, and class are present in the design, interpretation, and dissemination of experiments on the epigenetic effects of maternal care. As these experiments come to support claims about human motherhood through a dense speculative cross-traffic between epigenetic studies in rodents and psychological and epidemiological studies in humans, current research trends work to illustrate rather than interrogate existing stereotypes about maternal agency and responsibility. With this analysis, we offer a cautionary perspective regarding the potentials and challenges for new forms of collaborative biosocial knowledge practices emerging out of environmental epigenetics.