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. Author manuscript; available in PMC: 2012 Apr 1.
Published in final edited form as: Front Neuroendocrinol. 2011 Feb 4;32(2):114–123. doi: 10.1016/j.yfrne.2011.01.004

Figure 2. A Lumpers versus Splitters approach to sexual differentiation of the brain.

Figure 2

Studies on the sexual differentiation of the brain have been going on for 50+ years, providing a rich and complex collection of findings. Several fundamental principles arise from the dogma of early organizational effects of steroids determining adult reproductive physiology and sexual behavior. These can be lumped into broad categories. But elucidation of mechanism reveals highly unique region specific cellular pathways that underlie the organizational actions of steroids. Moreover, examination of sex differences outside of the context of reproduction reveals many new and possibly fundamental principles that both induce and reduce sex differences in brain and behavior. The relative lumping and splitting of various components is fluid and likely to change with additional new discoveries and reinterpretation of old ones. The colors used to designate each major category under Lumping is then used to designate the related set of individual findings under Splitting. New colors under Splitting indicates areas that are so recent as to not yet be associated with any fundamental concepts.