Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.
In this issue of Cell Host & Microbe, OhAinle et al., 2008 report that APOBEC3H, a potent innate retroviral restriction factor in primates, lost its function twice independently during recent evolution in humans, stressing an ever present trade-off between benefit and cost of protection against pathogens.