Growth hormone helps shape the body by regulating the growth of muscles and bones. It is released by the pituitary gland at the base of the brain and travels through the bloodstream. To act on a cell, the hormone must bind to a receptor on its surface, which then passes the signal into the cell. An international team led by Hugo Zeberg of Karolinska Institutet and Philipp Kanis of the Max Planck Institute for Evolutionary Anthropology found that the Neandertal version of this receptor has two changes that are not present in the version most common in modern humans.