Female full professors are less likely than men to co-author papers with assistant professors of the same sex, finds a study (J. F. Benenson et al. Curr. Biol. 24, R190–R191; 2014). Study authors calculated the expected co-author combinations for papers published from 2008 to 2011 by psychologists at 50 US and Canadian universities. They found 14 pairings of senior and junior women, compared with the expected 29, and 76 pairings of senior and junior men, compared with the expected 61. Women's tendency to pair with another woman of the same rank impedes their academic mobility, says co-author Joyce Benenson of Emmanuel College in Boston, Massachusetts.