Halfway into a mouse pregnancy, before the testes have even formed, the activity of 51 genes is different in males and females, says Eric Vilain of the University of California, Los Angeles. His team analysed 12,000 brain genes.
Note that other news accounts report 54 genes are involved.
It rebuts 30 years of scientific dogma that the hormones, estrogen and testosterone, alone were responsible for differences between the male and female brain. So the researchers were surprised then they found 54 genes produced in different amounts in male and female brains prior to hormonal influence. Eighteen of the genes were produced at higher levels in the male brains and 34 were produced at higher levels in the female brains.
This opens up some interesting possibilities. If a large set of genes all express one way in females and in a different way in males then it may become possible to manipulate subsets of the genes involved in making male and female brains to create people who are in some ways female and in other ways male. Also, by pushing the expression of the genes more in one direction or the other it may eventually be possible to make even more masculine and more feminine minds.
I have a basic rule: the more we learn about the genetic basis of human nature the more we will be able to manipulate it. Abuses are inevitable. Also, the culture wars about abortion rights will seem like the little leagues as compared to the future battles about ethics when it becomes possible to change human nature by manipulating the development of the mind. Real physical wars may end up being fought over different visions of what is allowable to do in creating offspring.
This report also brings up the question of whether any of those who want to undergo a sex change operation experienced during fetal development genetic expression patterns that are more like those the opposite sex. Also, the same question can be asked about homosexuals. The difficulty of answering these questions is that getting neurons out of a brain to test would pose ethical and practical problems and it would take years to wait to see if the fetal stage gene expression patterns have gene expression patterns that are, at least in some respects, more like the opposite sex? My guess is that the homosexuals will turn out to have various mixes of male and female brain gene expression patterns.
"Our findings may help answer an important question -- why do we feel male or female?" Dr. Eric Vilain, a genetics professor at the University of California, Los Angeles School of Medicine, said in a statement. "Sexual identity is rooted in every person's biology before birth and springs from a variation in our individual genome."
This is another nail in the coffin of the tabula rasa view of human nature.
This result may eventually be useful for more accurately identifying and treating those born with sexually ambiguous genitalia.
"If physicians could predict the gender of newborns with ambiguous genitalia at birth, we would make less mistakes in gender assignment," said Vilain.
This report follows and certainly builds on work by a team headed by Vilain reported a year ago that showed that the brain started getting sexual orientation before the SRY gene starts genital development. See the post Brain Gets Sex Orientation Before Genitals for more details.
Update: It would be interesting to compare liver gene expression patterns in homosexuals to heterosexuals to see if liver gene expression differs from male and female expression patterns in homosexuals.
In the November 1 issue of Genes & Development, Dr. Diane Robins and colleagues report on their discovery of two neighboring genes, Rsl1 and Rsl2, that repress male-specific liver gene expression in female mice. They found that female mice harboring mutations in Rsl genes aberrantly turn on male-specific liver genes, causing the female livers to adopt characteristically male patterns of gene expression.
If liver gene expression patterns were to turn out in some cases to be reliable proxies for brain gene expression patterns for genes that are sex-specific then that might make it easier to test for sex-specific gene expression patterns.
Update II: The UCLA press release contains more details on the Vilain study.
"We didn't expect to find genetic differences between the sexes' brains," Vilain said. "But we discovered that the male and female brains differed in many measurable ways, including anatomy and function."
In one intriguing example, the two hemispheres of the brain appeared more symmetrical in females than in males. According to Vilain, the symmetry may improve communication between both sides of the brain, leading to enhanced verbal expressiveness in females.
"This anatomical difference may explain why women can sometimes articulate their feelings more easily than men," he said.
Overall, the UCLA team's findings counter the theory that only hormones are responsible for organizing the brain.
"Our research implies that genes account for some of the differences between male and female brains," Vilain said. "We believe that one's genes, hormones and environment exert a combined influence on sexual brain development."
The scientists will pursue further studies to distinguish specific roles in the brain's sexual maturation for each of the 54 different genes they identified. What their research reveals may provide insight into how the brain determines gender identity.
Men and women really do think differently.
|Share |||Randall Parker, 2003 October 20 08:22 PM Brain Development|