I’ve just found this surprising study in Psychological Science that found a link between the point in the menstrual cycle of 77 white women and various measures of race bias.
Race Bias Tracks Conception Risk Across the Menstrual Cycle.
Psychol Sci. 2009 May 4. [Epub ahead of print]
Navarrete CD, Fessler DM, Fleischman DS, Geyer J.
Although a considerable body of research explores alterations in women’s mating-relevant preferences across the menstrual cycle, investigators have yet to examine the potential for the menstrual cycle to influence intergroup attitudes. We examined the effects of changes in conception risk across the menstrual cycle on intergroup bias and found that increased conception risk was positively associated with several measures of race bias. This association was particularly strong when perceived vulnerability to sexual coercion was high. Our findings highlight the potential for hypotheses informed by an evolutionary perspective to generate new knowledge about current social problems-an avenue that may lead to new predictions in the study of intergroup relations.
The research paper is online as a pdf if you want the full details.
The authors explain the findings as suggesting that women show a preference to their ‘in group’, those who more closely match their own background and lifestyle, when most fertile.
Menstrual cycle has been found to influence numerous preferences in women in earlier studies, including dressing attractively, preference for the type of fanciable person, including a preference for more ‘masculine’ features.
Indeed, cycles in oestrogen are known to alter dopamine function in the striatum, a deep brain structure.
pdf of menstrual cycle and race bias study.
Link to PubMed entry for same.
Mind Hacks 
Understanding these connections is interesting and has its uses, but I’m tired of having my gender medicalized and pathologized. Why are hormone fluctuations in men not studied as closely or publicized as widely? Women have been told plenty already about how their ‘instability’ resulting from having a menstrual cycle disqualifies them from any number of activities, especially leadership and responsibility positions, and in some countries, even being considered equal citizens. “What are you, on the rag?” is a common way of silencing a woman’s voice and invalidating her point of view. Research like this, presented without appreciation for the social context, only furthers and more deeply entrenches these harmful stereotypes.
Studies like this are patronizing to minorities, a typical British trait.
The unconscious patronization of minorities does not help anyone. For example, a study by Kent Harbor (1998) asked white university women to evaluate a poorly written essay. When they believed the writer was black, the women gave significantly higher scores and never strongly criticized essays. On the other hand, the women expressed harsh criticism when they thought the essays were written by a white person. Liberal authors will typically go on to cry about how this “inflated praise and insufficient criticism” could hinder minority achievement, but what about the effect on whites?
Even in social science where definitions are supposed to be explicit, the word prejudice has been overextended by guilt-ridden or just plain biased liberals or stupid leftists. Prejudice should be clearly defined as prejudging an individual. There is plenty of that going around everywhere in the world. Prejudice is not perception of general characteristics of some culture or ethnic group. Perception of general characteristics of a culture or ethnic group could be true (intelligent) or false (biased). To dislike some perceived characteristic of a culture or ethnic group is not prejudice. If an individual starts exhibiting some behavioral characteristic that one does not like, then it is not prejudice to dislike the individual for it.
I agree with Beth. I’m a historian of women’s health and when I see studies like these I feel like I’m in a time warp.
I seem to recall being told somewhere along the line in this discussion that men don’t have hormonal fluctuations. I came back here after seeing this article: http://jezebel.com/5498832/how-wall-streets-men-act-like-menstruating-women to point it out, but am not finding those comments again. Maybe I was thinking of another thread.
Still, here’s at least one example of a hypothesis about male hormonal fluctuations’ influence on behavior that could be tested / explored, were anyone so inclined.