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Some species in which females are dominant to males. Clockwise from upper left: spotted hyena, marmoset (photos by Jeff French), rock hyrax (Abraham Badenhorst) and ring-tailed lemur (James Barker).

Biology and Sex Differences Redux

A recent Pew survey showed that in 40% of American households with children, women were the major 'bread-winners'. In an interview on Fox News, conservative political blogger Erick Erickson responded to this survey by stating that it was "anti-science" for society to accept this role for women. "When you look at biology, when you look at the natural world – the roles of a male and a female in society and in other animals, the male typically is the dominant role. The female, it's not antithesis, or it's not competing, it's a complementary role", said Erickson. These statements ignited anew the discussion regarding "biologically-determined" sex roles in men and women.

An upcoming scientific paper by a group of UNO scientists in the College of Arts and Sciences has clearly shown that 'science' has no rigid proscriptions for what male and female roles are or what they should be in nature. The group, led by Jeff French, Varner Professor of Psychology, Biology, and Neuroscience at UNO, reviewed the published literature on species of mammals (the taxonomic group to which human beings belong) in which females are not only more aggressive than males, but in many cases are socially dominant over males. "In a host of species, females are clearly dominant to males in feeding competitions, in access to preferred locations for resting and sleeping, and in many other facets of social life", said French. Species in which females "rule the roost" include spotted hyenas, rock hyrax (a close relative of elephants), ring-tailed lemurs, marmosets, and hamsters.

In their paper, French and his group, including graduate students Aaryn Mustoe and Jon Cavanaugh, and research technician Andrew Birnie, also presented information on the biological origins of this sex-reversed pattern of dominance and aggression. In many cases, exposure to high levels of androgen hormones (like testosterone) during gestation or shortly after birth can 'program' the brain centers involved in regulating aggression and dominance in females, thus shaping the nature of aggression later in adulthood. In addition, the ability to form complex coalitions among females, particularly among related individuals (mothers, daughters, and granddaughters) can provide an important social route to female dominance in some species.

"In contrast to Mr. Erickson's characterization of male and female roles, our work shows that having simply having XX or XY chromosomes (the sex-determining chromosomes in female and male mammals, respectively) does not dictate what an individual's social role, social status, or aggression level will be", concluded French. "Nature has multiple ways of shaping sex roles, and our review confirms that evolution produces remarkable diversity in animals. This includes diversity in sex-typical patterns of dominance and aggression, including many cases where females are both more aggressive and more dominant than males." The paper will be published in an upcoming issue of the Proceedings of the Royal Society B – Biological Sciences.

Contact: Jeffrey A. French

Feature Archive


The study of the biological basis of behavior is one of the most rapidly growing
areas of life sciences, reflecting the importance of the fundamental and applied interest in how neurons work on an individual basis, and how collections of neurons mediate behavior  and cognition.

The College of Arts and Sciences at UNO has established the first undergraduate neuroscience degree program in the Nebraska system to educate students bound for graduate programs in neuroscience as well as various careers in the health or health-related fields.

Students working toward completion of this degree will benefit from the expertise of existing faculty in the UNO departments of Biology and Psychology along one of two tracks:  Molecular and Cellular Neuroscience or Integrative Behavioral Science.

An undergraduate major in neuroscience will place students in the position of
moving into one of multiple career trajectories upon completion of the degree.

First, graduates of the program will be in an excellent position to immediately and successfully be recruited by one of the more than 200 graduate programs in neuroscience and related areas, and pursue advanced degrees. These opportunities include working with faculty at UNMC’s growing training programs and opportunities.  The newly established Department of Pharmacology and Experimental  Neuroscience at UNMC brings together experts in neuropharmacology with those with expertise in neurodegenerative diseases, and new and exciting graduate programs are likely to emerge from this new department. Neuroscience and related disciplines constitute among the best funded and active programs at UNMC. The Center for Neurovirology and Neurodegenerative Disorders (CNND) and the associated Neuroscience Research Training Program (NRTP) at UNMC constitute an important employment and training outlet for graduates of an undergraduate neuroscience major.

Second, graduates from either of the proposed neuroscience tracks would have most or all of the required courses for admission to medical schools, veterinary programs, and a host of other health-related professional programs.

Third, graduates of the neuroscience major will possess intellectual and methodological skill-sets that will make them highly attractive for laboratory technicians and assistants in local, regional, and national university and medical school laboratories.

Fourth, the growing emphasis on pharmaceutical agents that affect psychological function is driving employment in corporate pharmaceutical firms, for which graduates of the neuroscience major would be competitive.

Finally, students will emerge from the major with the ability to think across disciplines, to formulate questions and seek answers, to interpret data and draw conclusions, and to effectively communicate the outcome of these processes to a target audience. This suite of skills will make neuroscience majors eligible for a variety of career opportunities that are outside of the discipline of neuroscience.