Ellen Breen is part of the Research Faculty in the Section of Physiology, Division of Pulmonary Critical Care and Sleep Medicine, Department of Medicine at the University of San Diego, California. Her research has focused on the molecular biology and physiology regulating the oxygen transport system. In particular she has focused on the interaction of the lungs, skeletal muscle and brain to provided sufficient oxygen during exercise and how these systems are compromised in many chronic diseases, such as chronic obstructive pulmonary disease. Recently, she started studying a very interesting evolutionary change in Hominins that took place about 2 million years ago. This involves the expression of the gene for CMP-Neu5Ac Hydroxylase (CMAH). Other primates express CMAH but due to a genetic mutation humans lost this hydroxylase which modifies a cell surface sugar, sialic acid. Her recent studies show that replicating this biochemical change in mice leads to remarkable improvement in endurance exercise capacity, mitochondrial function and overall oxygen utilization.