The problem of under-representation of women in science, particularly at the most senior levels, is not going to go away. Public discussion of the issue often focuses on the extent to which girls are encouraged to pursue scientific interests at school, or to which they are discriminated against at work. But a more readily addressable impediment obstructs the career paths of many female researchers in early- and mid-career: the absence of suitable childcare arrangements.
The issue of child care tends to arise at a crucial juncture in women scientists' careers, and there is a growing consensus that it can play a significant role in thwarting scientific ambitions. All over the world, even as the number of women who pursue graduate education continues to grow, women remain under-represented in senior scientific positions. Among the major scientific nations, the situation is perhaps most acute in Japan and in Germany, where women make up 30% of those starting graduate school, but only 6% of full professors.
Advocacy groups such as the Association for Women in Science frequently emphasize the need to encourage girls to do science at school, and to mentor women scientists early in their careers. They should place equal emphasis on the need for affordable day care. Without it, women scientists can be forced to choose between putting off having children, or having their careers derailed by motherhood.
Most major universities and laboratories offer some child-care options, but uneven access and affordability prevent anything resembling a working, national system in all but a few countries. These programmes vary widely in quality and even the best ones have significant shortcomings, as we report in this issue (see Small steps towards campus child care). Scandinavian nations and France offer some of the most comprehensive arrangements, but these are stretched thinly, with long waiting lists the norm. Most US universities offer child care, but the cost can be prohibitive to junior researchers.
Some employers have sought to address the affordability issue: the European Molecular Biology Laboratory in Heidelberg, Germany, for example, charges a fee of 10% of parents' combined income. Individual senior researchers have also chipped in to tackle the problem: Nobel laureate Christiane Nusslein-Volhard, head of the Max Planck Institute for Developmental Biology in Tübingen, set up a foundation last year to give five women scientists at the laboratory 
400 (US$490) a month for babysitting and domestic help, when she noticed that talented female research assistants were dropping out of science once they had children.
Uneven access and affordability prevent a working, national child-care system in all but a few countries.
The only systems that really work, though, involve government subsidies or tax incentives that enable the considerable cost of child care to be spread between the state, the employer and the employed. If women's representation in science is truly their objective, governments and research institutions must find a way to share the child-care load.
