Jonathan Barazzutti

The John Money Experiment, a twin study which ran from the mid-1960s onwards, was a real-world case study on the degree to which an individual’s gender identity is malleable.

David and Brian Reimer were two identical twins born in 1965 in Canada. Following a botched circumcision in infancy, David Reimer’s parents were advised by John Money to have him undergo sex reassignment surgery and raise him as a girl, socially and also medically via receiving estrogen and the construction of pseudo female reproductive organs. David, for all of his childhood, was raised by the name “Brenda”, and was never informed that he was born male. However, David Reimer reported that he experienced severe gender dysphoria as a child and had the desire to transition to be a boy, despite the social conditioning he was raised with. At the age of 15, following learning from his father about him being born a male, David assumed a male identity and his current name, later on receiving testosterone therapy to assist with a transition.

The experiment had extreme ethical problems with it and had a tragic ending. David Reimer reports psychological trauma due to John Money’s experiments, and the two twins were sexually abused on several occasions by Money. David ended up committing suicide at age 39. While it would be extremely unethical to deliberately put children through such an experiment again, its results provide a fascinating case study into the role that biology may play in an individual’s gender identity. If biological sex differences did not play a significant role in gender identity, then we would expect that neither child would have experienced gender dysphoria as said condition is by default rare.

Studies tend to report that around 1.2-4.1% of adolescents report a gender identity different from that assigned at birth. Given that as discussed by the American Psychological Association not all transgender or gender diverse individuals experience gender dysphoria, this number may be an overestimate for the actual prevalence of gender dysphoria among adolescents. However, assume that the 1.2-4.1% estimate is not an overestimate and that the real prevalence of gender dysphoria in adolescents is at the higher end of that estimate at 4.1%. Then, the probability of the twin combination occurring of both David and Brian both desiring to be male, assuming that the gender dysphoria rate exists at the same proportion in everyone, can be calculated using binomial probabilities. The formula is as such:

P = (gender dysphoria probability)*(1 – gender dysphoria probability) = (0.041)*(1-0.041) = 0.039 = 3.9%

In other words, assuming that gender dysphoria exists at the same proportion in everyone, the probability that such a result would have been achieved as the John Money Experiment result is at most ~3.9% under the most extreme assumptions. Clever readers who have an introductory statistics background will notice that there is a term for this probability. This probability is referred to as a “p-value”, or the probability of getting a given result in a study assuming the null hypothesis is true. Generally speaking, a result is considered “statistically significant” if the p-value is less than 5%, as is the case in this example. This means that in this case, it is reasonable to reject the null hypothesis, or the hypothesis that gender dysphoria was not more common among these twins. The fact that David who was raised female just so happened to get gender dysphoria, while Brian who identified as male the whole time didn’t, is highly unlikely and is consistent with the notion that a person’s gender identity is generally linked to their biological sex.

The anecdote is fascinating, but it is by no means the only evidence in favor of this hypothesis. Similar results were achieved by another study with a larger sample size, which found that all of the genetic males with a phallic birth defect that were raised as girls had interests and attitudes considered typical of males, and that many had reassigned to become male. Many sex differences emerge even prior to the recognition of sex or gender by children. Boys and girls aged 9-17 months old, an age where they show essentially zero signs of recognizing their own sex or the sex of others, still show marked differences in preference for stereotypically male or female toys. In fact, girls exposed to high levels of androgens in the prenatal and postnatal periods show increased play with boys’ toys and reduced play with girls’ toys, suggesting that differential levels of hormones between biological males and biological females mediate the relationship between biological sex and toy preference. Sex differences in behavior can be seen even earlier than when boys and girls are capable of playing with toys. For example, female newborns have been found to engage in eye contact for significantly longer periods of time than male newborns.

Psychological sex differences that exist due to sexual dimorphism can help to explain the various differences between men and women that exist cross-culturally, including in personality and interests. While there is variation in the specific ways that gender norms and roles can manifest across different societies and cultures, much of the bigger picture remains roughly the same no matter where one looks.

None of this means that exceptions cannot exist. Exceptions to these rules exist, and there isn’t anything inherently wrong with them. Some men have more feminine temperaments, and some women have more masculine temperaments. Similarly, there are some biological men and biological women who desire to identify with the opposite sex. While there are confounds in studies examining the neurological basis of gender identity, research suggests that gender dysphoria still has somewhat of a neurological basis. Hence, for some individuals gender transition may very well be an acceptable course of action. However, refusing to acknowledge the broader patterns that exist does harm to both the exception and the rule alike.