Turns out, there is now some evidence that the gender of session organizers has a significant influence on who ends up speaking in the more prestigious symposia sessions.
A recently published paper in PLOS One, "Stag Parties Linger: Continued Gender Bias in a Female-Rich Scientific Discipline", examined participation by women and men at conferences in a field in which women are in the numerical majority. Based on an analysis of 21 annual meetings of the American Association of Physical Anthropologists, they found that in the subfield of primatology:
1. Women gave more posters than talks; men gave more talks than posters.
2. The proportion of female participants was lower in symposia organized by men (29%) compared to those organized by women only (64%) or by both men and women (58%).
They found the same pattern for 12 annual meetings of the American Society of Primatologists.
Primatology is a field that has had more female than male participants since the early 1970s and where women have achieved substantial peer and popular recognition for their achievements (Jane Goodall, Dian Fossey). The results of this study suggest that even numerical dominance by females in a scientific field does not prevent gender bias. By looking at symposia participation, which is typically by invitation of the organizer, in relation to the gender of the organizer(s), the authors were able to say something about whether the underrepresentation by women at conferences might be due to lack of assertiveness by females or to bias. Whereas posters and regular talks are self-motivated, the more prestigious symposia reflect a choice made by the organizer. The results suggest that when men are the organizers, fewer women are invited to participate, but that men and women are equal participants in symposia organized by women (despite the larger numbers of women in the field).
Such bias may be unconscious on the part of the male symposia organizers. I'm just guessing that this is the case as the authors have no data either way. The authors of this paper, however, do state that they "cannot rule out" the possibility that male primatologists are more homophilic (homophily is preferential interaction with others who have similar attitudes, beliefs, or personal characteristics) than women. The idea is that male symposia organizers have to spend more time interacting with their invitees, both before and after the symposium (e.g., to jointly prepare a conference proceedings) and simply prefer to work with other males. Perhaps. The jury is still out on that one. But my guess is that this behavior is not restricted to male primatologists.
The finding that women gave more posters than talks and men the reverse is troubling and suggests the possibility that women are preferring the less visible presentation mode. Although the study indicated that men were 12% more likely to request an oral talk over poster than women, which might explain the gender difference, the authors suggest that there still might be some bias occurring at the presentation selection/assignment stage (by the conference organizers). Their data were pretty weak on this point, however.
In any case, this is yet another example of why it is important for women to be assertive in promoting themselves and their science. We may need to encourage female students to give oral presentations. As for bias in inviting speakers, one solution is for more women to organize conference symposia and ensure that women are well represented in the speaker lineup.