Stereotypes, role models played by teachers and social norms influence girls' academic self-concept and push girls to choose humanities rather than science. Do recruiters reinforce this strong selection by discriminating more against girls in more scientific subjects? Using the entrance exam of a French higher education institution (the Ecole Normale Superieure) as a natural experiment, we show the opposite: discrimination goes in favor of females in more male-connoted subjects (e.g. math, philosophy) and in favor of males in more female-connoted subjects (e.g. literature, biology), inducing a rebalancing of sex ratios between students recruited for a research career in science and humanities majors. We identify discrimination by systematic differences in students' scores between oral tests (non-blind toward gender) and anonymous written tests (blind toward gender). By making comparisons of these oral/written scores differences between different subjects for a given student, we are able to control both for a student's ability in each subject and for her overall ability at oral exams. The mechanisms likely to drive this positive discrimination toward the minority gender are also discussed. (Contains 15 tables, 3 figures and 33 footnotes.)