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It may seem obvious, but biological males differ significantly from biological females in many aspects of physiology and behavior. These differences have profound implications for the treatment and prevention of diseases such as cardiovascular disease, asthma, renal failure, cancer, and diabetes — implications long overlooked, but gaining currency perhaps due to the increasing number of women in research.
Many studies, including mine, have demonstrated striking sex-based differences in the brains of rodents. For example, my research is focused on the medial preoptic area (MPOA), a small cluster of cells at the front end of the hypothalamus near the bottom of the brain. This area plays a critical role in the regulation of male sexual behavior.
I study hamsters, which are strongly influenced by pheromones. Using fos (a protein that reflects neuronal stimulation), my research has determined that pheromones stimulate the MPOA in males but not in females. My colleagues and I then showed that the lack of stimulation in the female is the result of sex differences in the density and plasticity of synapses.
We also found that the number and type of neurons in the MPOA were sex-specific. Unlike in males, the female MPOA contains a large population of neurons with multiple nucleoli (structures that translate ribosomal RNA into proteins). While the role of these neurons has yet to be determined, fewer of them are stimulated by pheromones. Thus, males and females show fundamental differences in both the structure and the function of the MPOA that may underlie differences in behavior.
While my studies are focused on a tiny yet important area of the brain, many studies, aided by enhanced optical imaging technologies, have identified sex-based differences in the neurons, synapses, and chemistry of the hippocampus, amygdala, and cortex of a variety of laboratory species. They have also been reported in the human brain in areas linked to social behavior, stress, and addiction. Moreover, additional studies have shown that differences in the brain can be correlated with differences in behavior, supporting a role for the morphological findings. Yes, the two sexes have very different brains.
Why is this important, and what should we do with this data?
Well, for one, we must remember that different means just that; it does not imply less or more. In fact, some areas of the brain are larger in males and others are larger in females. Instead of judging one sex against the other, we should continue to investigate these findings. Efforts to understand human behavior in health and in disease can only be helped by understanding fundamental differences in morphology and function.
For example, leadership practices have recently begun to celebrate more collaborative and inclusive styles because they are ultimately more successful. Research suggests that inclusive leadership is a hallmark of female leaders. The difference in style could very well be related to differences between the male brain and the female brain. For example, the brains of female laboratory animals contain more oxytocin, the hormone that promotes social interactions — and, if confirmed in humans, it could underlie females’ bent to be more collaborative.
It is important to keep an open mind and remain curious rather than make facile judgements. We should take an object lesson from Lawrence Summers, a former president of Harvard University who resigned, in part as a result of a 2005 speech in which he suggested that the under-representation of women in science and engineering might be the result of a “different availability of aptitude at the high end,” and less attributable to bias and socialization. In fact, it has been well-documented that men and women produce similar math scores until about middle school, when social norms disrupt innate abilities.
So we must be slow to generalize until we have all of the facts. And we must remember that scientific data is derived from populations that, by definition, include variety and overlap in the regions between the traits. These differences should be approached with curiosity and appreciation, because they provide the tools we require to learn and thrive.
Meet the author
Jennifer Swann, Ph.D., is a professor in biological sciences at Lehigh University in Bethlehem, Pa., focusing on behavioral neuroscience. She is also the director of the school’s Student Success program in its College of Arts Sciences.
Swann is an accomplished scientist who has published more than 100 peer-reviewed articles, abstracts, book chapters, and proceedings in neuroscience, endocrinology, and circadian rhythms. Her work has defined multiple circadian oscillators, identified the sex-specific effects of gonadal hormones, and uncovered a novel role for growth factors in the expression of sexual behavior. Swann has served on professional development committees for the Society for Neuroscience and the Society for Behavioral Neuroendocrinology, in addition to a number of advisory boards, among them the Capstone Institute at Howard University, the neuroscience program at Delaware State University, the Ascend program at Morgan State University, and the Penn State Eberly College of Science.
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