The diversity of the typical American research university is widely admired, but is fashioned mainly on the basis of students and staff recruited from abroad. The universities have done less well at harnessing the talents of the racial minorities within the US population.

So-called under-represented minorities — African Americans, Latinos and Native Americans — formed more than a quarter of the American population in 2000, and are projected to account for more than 40% of it by 2050. Yet according to a 2005 study of 50 élite universities, undertaken by Donna Nelson, a chemist at the University of Oklahoma, they account for only 3% of tenured or untenured faculty in mathematics, physics, chemistry, biology and astronomy. Numbers are only slightly higher in engineering (4.6%).

Sharp economic divisions between whites and minorities in the United States makes it unlikely that any solutions confined to academia itself will ever achieve parity. It remains the case, however, that universities and their science departments could be doing more to enrich the diversity of their faculty.

Departments often pin the blame for the lack of minority recruitment on the small 'pipeline' of minority PhD holders, saying that universities compete for the few qualified minority candidates available. That line of thinking has contributed to the emphasis on boosting the flow of minorities through PhD programmes, and several laudable mentoring and fellowship initiatives, such as the Ford fellowships, exist to do that. But studies show clearly that faculty diversity has not kept pace with increasing diversity in the PhD pool.

One aspect of the problem concerns the tendency of departments to go out of their way to recruit minority candidates only to replace previous minority representation. In one study of science and engineering departments in 27 universities, of 1,500 faculty hired during 2000–04, only 157 were African American, Latino or Native American. But nearly three out of five of the new hirings merely replaced minority faculty members who had left the institution.

This is the proverbial 'revolving door' in action. Under-represented minorities are brought in as assistant professors, sometimes through special programmes that aim to improve diversity, only to leave shortly thereafter. Universities that focus on recruitment without placing equal emphasis on retention are not going to achieve the diversity that they seek.

Any successful assault on the persistent problems that universities have faced in nurturing diversity is likely to require the active involvement of under-represented minority faculty themselves. But this group is hard to unify, comprising as it does people who hail from disparate backgrounds and who are shaped by different experiences and social pressures. It can be hard to unite such a diverse group behind a single cause, yet their ranks are so small that full participation is crucial.

Discrimination, where it exists, may be hard to prove in individual cases, but can be identified by collecting appropriate, campus-wide data. Universities need to keep careful track not just of how many under-represented minority researchers they hire, but of how long they stay. The 27-university study found that institutions were rarely tracking data about departures alongside data about hiring.

Tenured faculty members must also learn to recognize the modern face of racial discrimination. This can take many subtle forms: neglecting to recommend a minority colleague to speak at a conference, subconsciously assuming that a minority researcher has a lesser role in a collaboration, or failing to recognize the added time a minority assistant professor may spend advising minority students.

The controversy at the Massachusetts Institute of Technology (MIT) over biological engineer James Sherley's tenure (see page 762) has pushed the institute to embark on a new study that will evaluate racial disparities among its faculty. It is a project that MIT has discussed but left undone for years, and a step that could sensibly be followed by other leading universities. It shouldn't take a hunger strike to prod them into action.