These conserved differences constitute a signature of sex differences in the brain, the researchers said. More obvious gender differences have been preserved throughout primate evolution; examples include average body size and weight, and genitalia design. This novel study focuses on gene expression within the cerebral cortex - that area of the brain that is involved in such complex functions in humans and other primates as memory, attentiveness, thought processes, and language.
For the study, 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. The results suggested that variation in expression of genes in the brain might be an important component of behavioural variation within as well as between species.
The differences could also explain sex variations in mental health and neurological diseases: women, for instance, are more at risk of depression and Alzheimer's, the authors noted.
"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," said Professor Elena Jazin of Uppsala University.
Lead author Bjƒ¶rn Reinius noted 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.
The study is published June 20th in the open-access journal PLoS Genetics.