This is a post by Lisa Barnett reprinted here with permission and extracted from a discussion at the TGIMormons Yahoo Group:
I have attached an article that I read recently. It is a research article entitled “Callosal Shapes at the Midsagittal Plane: MRI Differences of Normal Males, Normal Females, and GID” and it is available on the internet. The article is about measurements taken by MRI of the corpus callosum (CC), which interconnects the two cerebral hemispheres of the brain, and has been widely considered to have differential characteristics according to sex. The researchers have presented the measurements in terms of a single characteristic value. The article requires a complete read and I will not attempt to summarize it here but recommend that you read it for yourselves. I simply wish to make a couple of comments with regard to the article.
First, I think that this research article reflects what Jim was recently talking about with regard to placement of individuals on some kind of X,Y plane depending on each person’s percentage of femaleness (or maleness). The data in the paper is presented as histograms and show that, for large populations of males and females, a somewhat normal distribution of the measured characteristic is seen for each gender and that the distribution for the female population (mean .3918) is indeed offset from that of the male population (mean .4689). However, it also shows that the measured distributions of the characteristic parameter for both sexes have significant overlap; that is, there are many females who have the same size characteristic as many males have. You could say that such men and such women show equal percentages of femaleness and maleness.
The data suggests that there is a continum between what is male and what is female and that all of us lie somewhere along this continum. However, the research shows that there are two maximums along this continum with the smaller value being characteristic of females and the larger being chacteristic of males. This seems consistent with the idea that, in general, society categorizes all people into a gender binary even though, in reality, as individuals we only fit somewhere along a continum between female and male. There are, of course, a large number of such parameters that differentiate us between male and female and it is some combination of all of these parameters that result in what we refer to as our gender identities and sex which may or may not be consistent with the gender or sex that society assigns to us.
So, the first thing that I take away from this article is that, while it can be shown that a certain part of the brain can be differentiated according to size between a population of self identified females and a population of self identified males, individuals from both sexes can have the same measured size. For example, there are many females and many males in the entire population that have a characteristic size of 0.45. One could say that women having this size characteristic are more masculine than the average woman and men having this size are more feminine than the averate male even though they identify as being men or being women. However, there is also a group of people upon which these measurements were made who self identify as being either MTF or FTM GID.
It is interesting to me that these two groups show a distribution of the parameter that is similar to self identifying females for the MTF population and to self identifying males for the FTM population. This is probably no surprise to most of us on this site. The authors of the paper go so far as to suggest that their research may ultimately lead to a physical test that can be performed to determine if an individual has a male or female gender identity. I think they are being overly optimistic in this regard, as their own research points out.
For example, if you have an individual with a measurement characteristic of 0.45 you cannot say with any certainty that the person is female, male, MTF or FTM. You can only say that they lie on the female side of the male norm or on the male side of the female norm. Perhaps, in time, with the measurement of many separate sex differentiated parts of the brain and/or body of an individual, one can eventually arrive at a statement that the individual is essentially female or essentially male but I doubt that we will ever arrive at a definitive conclusion that someone is male or female, but only a statement of the probability that the individual is male or female.
I believe that their research does provide one very important finding that they fail to mention. It is this: They have shown that a group of people who self identify as female have a characteristic distribution that is offset from that of people who self identify as male. They have also shown that a group of people who self-identify as MTF have a characteristic distribution that is similar to the group who self identify as female and they have shown that a group of people who self-identify as FTM have a characteristic distribution that is similar to that of the group who self identify as male. No one questions the groups of men and women who self-identify as men or women as being anything other than what they say they are. Since no measurement is available to determine if a group of transgender people are what they say they are, the researchers must have had to rely on what each individual in these two groups said they were.
One therefore has to conclude from the data that, as a group, people who self-identify as being transgender (i.e., transsexual) are telling the truth because, as a group, their characteristics are similar to declared females if they are MTF or to declared males if they are FTM. To me, this research supports the idea that the best way to determine the gender of a child or adult is to let them tell you who they are, because, as a group, they will tell you the truth when asked in a non-threatening environment. Just some of my thoughts. I would be interested in hearing everyone’s views on the research.