Middle childhood growth and development in the evolution of human life history

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Humans are characterized by a uniquely extended period of dehydroepiandrosterone (DHEA) secretion, yielding blood concentrations 10-fold those of chimpanzees, our species' closest living relative. This adrenal neurosteroid has been associated with longevity and plays an important role in regulating brain development. A number of non-human primates secrete very low levels of this hormone and the reason for these interspecies differences is unclear. The investigators use comparative primate endocrine, genetic, and morphological data to examine whether DHEA secreted by the adrenal gland may have contributed to brain steroid input during human evolution and provide insights into the biological mechanism of adrenal steroids in primate body and brain. This research fosters international collaboration, supports the training of undergraduate and graduate students, and develops public science outreach activities at zoos.The developmental period in humans and great apes is marked by middle childhood growth (adrenarche), the post-natal increase in the adrenal hormones dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS). Both hormones are also secreted in the brain and have been associated with longevity and brain maturation. However, adrenarche is not apparent in lower primates, and the reasons for these interspecies differences are not well understood. This project uses endocrinology, microscopy and genetics in a comparative framework to examine the origins of adrenarche and its potential impact on primate brain and life history traits. Adrenal steroids and the enzymes necessary for steroid synthesis are quantified peripherally in living nonhuman primates as well as centrally in human and nonhuman postmortem brains to determine the connections between age, brain function, and adrenal steroids in primate life history. This study can impact our understanding of adrenal function in regulating primate development and contribute to debates about the role of DHEA in human evolution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.