Sex Differences in Disease (IMAGE) Arizona State University Caption There are longer-term evolutionary explanations and more immediate explanations for sexual dimorphism in immune function. The female immune system must compensate for the unique DNA of the placenta and immune-modulation during pregnancy. The placenta is phylogenetically shared across therian mammals, but with additional unique evolutionary pressures including invasive hemochorial placentas in eutherian mammals. Dimorphism in immune function in response to placentation and pregnancy occurs via the direct impact of reproductive hormones on immune function, as well as through heritable variation in sex chromosome gene content and dosage. Although evolution has shaped these sex differences over millions of years, industrialized urban populations experience exacerbated sex differences in hormone mechanisms as well as reduced pregnancies compared with non-industrialized populations. Credit <em>Trends in Genetics</em> Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.