Researchers have determined that there are hundreds of biological differences between the sexes when it comes to gene expression in the cerebral cortex of humans and other primates. These findings indicate that some of these differences arose a very long time ago and have been preserved through evolution. These conserved differences constitute a signature of sex differences in the brain.

Many more obvious gender differences have been preserved throughout primate evolution; examples include average body size and weight, and genitalia design. This study, believed to be the first of its kind, focuses on gene expression within the cerebral cortex. The cerebral cortex is involved in many of the more complex functions in both humans and other primates, including memory, attentiveness, thought processes and language.

The researchers measured gene expression in the brains of male and female primates from three species: humans, macaques, and marmosets. To measure activity of specific genes, the products of genes (RNA) obtained from the brain of each animal were hybridized to microarrays containing thousands of DNA clones coding for thousands of genes. The authors also investigated DNA sequence differences among primates for genes showing different levels of expression between the sexes.

"Knowledge about gender differences is important for many reasons. For example, this information may be used in the future to calculate medical dosages, as well as for other treatments of diseases or damage to the brain," says team leader Professor Elena Jazin, at Uppsala University.

In addition to the results mentioned above, the researchers also report on evolutionary speeds in genes that have been identified as male or female-oriented. This could provide clues about the power of natural selection processes during the evolution of primates.

Lead author Björn Reinius notes that the study does not determine whether these differences in gene expression are in any way functionally significant. Such questions remain to be answered by future studies.

Article: Björn Reinius, Peter Saetre, Jennifer A. Leonard, Ran Blekhman, Roxana Merino-Martinez, Yoav Gilad, Elena Jazin, 'An Evolutionarily Conserved Sexual Signature in the Primate Brain', PLoS Genet 4(6): e1000100. doi:10.1371/journal.pgen.1000100