Tribute to Dr Milton Diamond: Twin Studies of Transsexuality
I met Dr Milton (Mickey) Diamond at a biennial conference of the International Society for Human Ethology, but I cannot recall the year or the location. I do recall that our meeting occurred some time ago and that we developed a working relationship and friendship that lasted over the years. Mickey was an expert in the biological bases of sexual development and identity, launching the only relatively large-scale twin study of transsexualism of which I am aware. He was also consumed with finding answers to questions surrounding his thinking on a landmark case of Canadian twin infants that involved the sexual reassignment of one MZ male cotwin. Prior to reviewing that case and our collaboration on an unusual pair of transsexual twins (Segal & Diamond, Reference Segal and Diamond2014), I provide a brief overview of Mickey’s personal and academic background. Much of the material was drawn from a statement issued by the John A. Burns School of Medicine (2024). His photo is displayed in Figure 1.
Dr Milton Diamond. Courtesy of Connie Brinton-Diamond, Mickey’s wife.
Brief Biography
Mickey Diamond was born in New York City on March 6, 1934. He was one of three children of Jewish immigrants, Aaron and Jennie (Arber), who entered the United States from Ukraine. The family owned a series of grocery stores (Risen, Reference Risen2024). His neighborhood friends were predominantly Irish, explaining why he was given the nickname Mickey. He attended the prestigious Bronx High School of Science (which I attended years later) and the City College of New York. He majored in physics, then biophysics, while joining ROTC to help finance his studies. It it likely that the courses he took in endocrinology and animal behavior during an extra college semester are responsible for his interests in human sexuality. Following graduation, Mickey joined the Corps of Engineers and was stationed in Japan. Upon completing his commission, he was encouraged to pursue graduate studies of anatomy, endocrinology and behavior, which he did at the University of Kansas, in Manhattan. He completed a doctoral thesis on the effects of prenatal hormones on sex, gender, and behavior in both human and nonhuman animals.
Mickey’s next academic career move was to the medical school of the University of Louisville, in Kentucky. That position was followed by an appointment as associate professor of anatomy at the John A. Burns School of Medicine, at the University of Hawaii. Mickey also directed the Pacific Center of Sex and Society, a named unity within the medical school.
Selected Scholarship
Mickey Diamond authored numerous articles on many aspects of human sexuality, including homosexuality, sex crimes, and gender-variant children. Too numerous to name, I will list two that, in my estimation, made the greatest impact on the field. The first is his 1997 paper that exposed the truth about the sexual development and identity of the male twin that Dr. John Money, at Johns Hopkins University, in Baltimore, Maryland, tried to change into a girl. (More on that episode can be found below.) The second article is his latest analysis of twin concordance for transsexuality.
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Diamond, M., & Sigmundson, H. K. (1997). Sex reassignment at birth: Long-term review and clinical implications. Archives of Pediatrics & Adolescent Medicine, 151, 298−304.
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Diamond, M. (2013). Transsexuality among twins: Identity concordance, transition, rearing, and orientation. International Journal of Transgenderism, 14, 24−38.
Among his many academic honors are the British International Prize from the Gender Identity, Research and Education Society (1999), the Norwegian Diversity Prize for research on transsexual and transgender individuals (2005) and, most recently, a medal from the World Association for Sexual Health (2015).
Passing
Mickey Diamond passed away on March 20, 2024, just two weeks after his 90th birthday. He leaves behind his second wife Connie, four daughters and six grandchildren, as well as three stepchildren and eight stepgrandchildren. He also leaves behind a vast collection of colleagues who found his work inspirational. He will he missed.
Short Summary of Recent Twin Studies of Human Transsexuality: Focus on Contributions by Dr Milton Diamond
A comprehensive summary of twin studies of transsexuality introduces Diamond’s (2013) independent study, conducted at the University of Hawaii. Obtaining references from international colleagues, Diamond received material on 43 sets of twins. All studies appeared to be case reports given that 43 references were listed; my report (Segal, Reference Segal2006) contained material on two pairs, but was counted only once. Organized by zygosity and sex, the overview yielded 17 monozygotic (MZ) male sets, 10 diygotic (DZ) male sets, 14 MZ female sets, and 2 DZ female sets. Concordance for transsexuality was reported for 8 MZ male pairs, 1 DZ male pair, 5 MZ female pairs and no DZ female pairs. These findings are consistent with genetic effects.
Diamond (Reference Diamond2013) combined these data with new data he obtained from requesting referrals from colleagues. This request yielded 69 additional pairs for a total of 112 pairs. He found concordance for 13/39 (33%) MZ males, 1/21 (5%) DZ males, 8/35 (23%) MZ female, and 0/15 (0%) DZ females, further evidence of genetic effects. He also found that the twins’ gender identity was based more on genetics than on their rearing. Subsequent to this study, research has yielded findings that both support (Kauffman et al., Reference Kauffman, Guerra, Thompson and Stark2022; Bidaki et al., Reference Bidaki, Salimi, Naderi, Amiri and Dehghani2023) and refute genetic influence on gender identity (Karamanis et al., Reference Karamanis, Karalexi, White, Frisell, Isaksson, Skalkidou and Papadopoulos2022).
To my knowledge, Diamond and I published the only case report of transsexualism in MZ twins reared apart (Segal & Diamond, Reference Segal and Diamond2014). The twins (whom we identified as AT and LT) were anatomical males, separated due to the poor health of their biological mother. LT was raised in a fairly permissive home in which his gender identity and cross-gendered behaviors were accepted. In contrast, AT was raised in a disciplined home in which his gender identity and cross-gendered behaviors were rejected. The twins learned of each other’s existence at age 15 years when a reunion was arranged. Prior to meeting, by age 8 both had engaged in cross-dressing and felt they should have been born as the other sex. Both twins eventually underwent sexual reassignment, decisions made independently from their cotwin. Firm conclusions cannot be drawn from individual case reports, but this pair adds to the larger literature supporting genetic influence on transsexualism.
Landmark Twin Case: The Wisdom of Dr Diamond
Most people are familiar with the famous case of an accidentally castrated MZ male twin infant and the failed attempt to change the child into a girl (Colapinto, Reference Colapinto2013). In brief, in the mid 1960s, an incorrectly performed circumsion destroyed the penis of a young Canadian twin. His distraught parents sought the assistance of Dr John Money, based on his respected work with intersex children. Money advised the family to change the child into a girl by means of hormones, surgical procedures, and rearing. Clearly, Money saw this case as a rare cotwin control experiment, since he could compare the developmental progress of the altered twin with that of his twin brother.
Over the years, Money insisted that the child was progressing well, spreading the belief that it was possible to alter sex and gender identity via medical and psychological means. However, Milton Diamond questioned that conclusion and spent years trying to locate someone who had worked closely on the case. He finally found Dr H. Keith Sigmundson. Sigmundson was a psychiatrist who had been associated with the case, but had never come forward with his knowledge that the twin’s transition from male to female was not working. Diamond pursuaded him to co-author a paper detailing the case and its outcome; the result continues to be a significant contribution to this field (Diamond & Sigmundson, Reference Diamond and Sigmundson1997). To quote from this paper:
Long term follow-ups of case reports are unusual but often crucial. This up-date to a case originally accepted as a ‘classic’ in fields ranging from medicine to the humanities completely reverses the conclusions and theory behind the original reports. Cases of infant sex reassignment require inspection and review after puberty; 5 and even 10 year post sex reassignment follow-ups are still insufficient. (p. 302)
Without the wisdom and perseverance of Dr Milton Diamond, the lives of many children and their families would have been irreparably harmed. As Mickey was fond of saying, the sexual organ is between the ears, not between the legs.
Twin Research Reviews
Loss of a Twin Brother
New Reading. Research shows that the loss of a twin sibling is a devastating event for twin survivors. Research also shows that the grief intensity associated with losing an MZ cotwin somewhat exceeds that associated with losing a DZ cotwin; of course, these average findings may not apply to individual cases (Segal et al., Reference Segal, Miller and Niculae2022). Less, however, is known about the experience of a female twin facing the loss of a twin brother. To better understand the nature of this loss, a recent personal account is available, beautifully written by surviving twin, Lucie Boulanger. Her book, The Hidden Face of Gemellity: Twins, From Conception to Death (Boulanger, Reference Boulanger2024), tells the moving story of mourning the loss of her brother. Her account is supplemented by the experiences of 60 other twins (both MZ and DZ) whose cotwins passed away either in utero or during their lifetime. This book will be insightful for bereaved twins, as well as families, researchers, clinicians and counselors.
Oxytocin Adminstration During Twin Delivery
The optimal dosage of oxytocin administered during an elective cesarean delivery has been uncertain. Postpartum hemorrhage (PPH) is of particular concern in such pregnancies. Oxytocin can prevent PPH, but because it may have serious physiological effects, it is important to determine the proper dosage.
In an attempt to resolve this issue, a Canadian research team applied a double-blind design in an analysis of 30 mothers carrying twins (Peska et al., Reference Peska, Balki, Pfeifer, Maxwell, Xiang, Downey and Carvalho2024). Participants were at 36 weeks gestation, or greater, but were excluded if severe complications were apparent. It was anticipated that the optimal dosage would exceed 0.5 international units (IUs), but would not exceed 5 IUs. Doses could be .5, 1, 2, 3, 4 or 5 IUs; the first patient received 0.5 IUs, while the doses of subsequent patients were determined by the response of the proceeding patient. It was concluded that women carrying twins should receive 5 IUs of oxytocin over at least one minute when undergoing neuroaxial anesthesia (placement of a local anesthetic in or around the central nervous system; Olawin & Das, Reference Olawin and Das2022); this amount is much larger than the dose administered to women carrying singletons (0.35 IUs).
Models of Monochorionic Twinning
An approach to studying the processes underlying monochorionic twinning are of great interest, given that this subset of MZ twins is at high risk for physical complications. There are, however, ethical limitations surrounding research on human embryos. An international research team, headed by Dorian G. Luijkx at Maastrict University, in the Netherlands, developed the first in vitro models in an attempt at unraveling events responsible for monochorionic twins (Luijkx et al., Reference Luijkx, Ak, Guo, van Blitterswijk, Giselbrecht and Vrij2024). The models consist of twin blastocysts that the researchers labelled ‘blastoids’, derived from human pluripotent stem cells (cells capable of self-renewal and the potential to generate all cells of the body’s tissues; Romito & Cobellis, Reference Romito and Cobellis2016). The researchers showed that ‘twin blastoids’ have greater potential for implantation than single blastoids. However, they caution that it is unclear how much their procedures induce twinning. They note that the models define new areas for studying twinning, possibly suggesting ways of identifying events linked to twin formation and implantation.
Twins’ Brain Responses to Watching Film
A fascinating twin study of movie watching adds to the list of disciplines adopting twin methods for examining novel hypotheses and questions (Schmälzle et al., Reference Schmälzle, Lim, Wu, Bezbaruah and Hussain2024). A prior study by these investigators using neuroimaging techniques showed that brain responses were similar across viewers in an American sample (Schmälzle et al., Reference Schmälzle, Lim, Wu, Bezbaruah and Hussain2024). The present study anticipated that brain responses using an Australian sample would correlate with those of the American sample. This expectation was fulfilled. A unique addition to this phase of the project was that the Australian sample was composed of 100 pairs of adolescent twins recruited from the Queensland Twin Adolescent Brain (QTAB) dataset. Only twin pairs concordant for righthandedness were studied, given brain differences between right- and lefthanders. The movie stimulus used was Partly Cloudy, a 5-minute silent animation film, developed by Pixar, featuring a cloud named Gus that creates babies for storks to deliver. The babies have unusual features. The relationship between Gus and the stork is challenged over the babies’ appearance, causing Gus to feel sad; however, the two partners eventually reconcile. Analyses of brain activity showed that the two samples responded in similar fashion; however, the twins were more alike than the nontwin participants.
The investigators concluded that the twins’ shared genes and shared environments explained their results. This study, while innovative, did not specify the number of MZ and DZ twins; it is possible that only MZ pairs were examined. It was also not explained how the zygosity of the pairs was determined; presumably this was done as part of the twins’ enrollment in the registry. If DZ pairs were not included in the study, it would be important to do so to gather evidence supporting the current conclusion. A sample of MZ twins reared apart and a sample of near in age adoptees (virtual twins) would shed further insight into the effects of shared genes, shared environments, and nonshared environments on responses to movie viewing.
Human Interest
Oldest Conjoined Twins Pass Away
Lori and Dori (Reba/George) Shappell were born on September 18, 1961 to a West Reading couple, Franklin and Ruth Shappell (Sandomir, Reference Sandomir2024). The couple had six other children, three girls and three boys. The twins are survived by their father and siblings; their mother passed away in 2019. The twins’ passing on April 7, 2024, at the age of 62, was widely acknowledged in the press, although their cause of death was not provided. The twins, who were joined at the skull, had been given little chance of surviving. Instead, they beccame the second oldest conjoined twins to survive, as indicated in the Guinness World Records.
The twins were classified as craniopagus, meaning that they could be joined at any part of the skull except the face, foramen magnum (one of several openings in the base of the skull), skull base, and vertebral column. In contrast, cephalopagus twins share a cranium with either one composite face or two faces on opposite sides of the conjoined head (Baba, Reference Baba2020). Lori achieved normal human stature, whereas her sister, Reba, was small and navigated through life sitting on a high stool with wheels.
I spoke with the twins during the writing of my first book, Entwined Lives (Segal, Reference Segal1999). They ended the conversation with an amazing story: The twins visited a liquor store to purchase a gift for a friend. The shopkeeper asked Reba for proof of age — then he agreed to sell the bottle to Lori if she made the purchase.
Twins Discordant for Child Abuse
The New York Times summarized a Swedish study reporting that an identical twin who suffered maltreatment was 1.2 times more likely to experience a mental illness than his or her unaffected cotwin (Barry, Reference Barry2024). The risk of mental illness for an abused fraternal twin increased his or her risk by 1.7 times. (The greater risk reported for fraternal twins is surprising. The original article indicated that exposure to emotional neglect or abuse increased the risk for psychiatric disorder; see Daníelsdóttir et al., Reference Daníelsdóttir, Aspelund, Shen, Halldorsdottir, Jakobsdóttir, Song, Lu, Kuja-Halkola, Larsson, Fall, Magnusson, Fang, Bergstedt and Valdimarsdóttir2024). The elevated risk was illustrated with reference to identical twins Dennis and Douglas. The twins’ experiences were closely aligned except that Dennis was the victim of attempted molestation when he was 13 years old. Subsequently, he had a series of failed relationships and period of depression. He then experienced a major depressive episode at age 50. In contrast, his unaffected twin brother was happily married, raised a family, and became religious.
There is some evidence that twins are more likely to be abused than nontwins, and that one twin is more likely to be abused than both twins (Segal, Reference Segal2017). In the first case, the unanticipated challenges of raising two infants at the same time could conceivably trigger abusive tendencies in couples with limited resources and difficult temperaments. In the second case, it appears that abuse is more likely to be directed to the twin perceived to be less healthy and/or less physically attractive. It is fortunate that research in this area is continuing.
Twins Married to Twins
Twins married to twins are a unique subset of quartenary couples and their children are a unique subset of legal first cousins. (Quarternary marriages, strictly defined, are comprised of two married couples and their children living together with the goals of companionship, division of labor, and increased adult role models for children; see Casler, Reference Casler1974). In 2020, Vanessa — an identical twin — was working as a personal trainer when a client introduced her and her twin sister, Kerissa to identical twins, Lucas and Jacob Sealby. The more extroverted pair members (Vanessa and Lucas) and the more introverted pair members (Kerissa and Jacob) paired off. The couples’ marriages took place in 2022 and 2023 respectively. All four twins, who are active in sports, now reside in the Pacific Northwest in neighboring homes. Vanessa and Lucas are the parents of daughter Sophie, age 20 months, and Kerissa and Jacob are the parents of daughter Adrian, age six months (Lyttle, Reference Lyttle2024). The four twins rarely argue and if they do the matter is settled in minutes. They believe this is because they are used to being twins and resolving disagreements quickly.
Kerissa admitted that she and her sister have similar tastes in men. However, she also claims that the two husbands have very different personalities and look quite different. I have always maintained that studying these quarternary couples can reveal a great deal about the subtle features of identical cotwins’ behavioral and/or physical traits that explain personal attraction or disinterest. This information would have implications for partner choice among non-twins, as well. I intend to consider this as I prepare to write my next book.
Rare Quadruplet Set Delivered
A rare set of quadruplets was delivered on May 1, 2024 to Mercedes Sandhu, at Texas Children’s Hospital, in Houston (Caplan, Reference Caplan2024). The infants’ mother is 34 years of age and her spouse is 37. Their four identical daughters — Hannah, Lucy, Rebecca and Petra — were born at 29 weeks, 3 days gestation and conceived naturally. The twins shared a placenta, making them a high-risk monochorionic set. In fact, a decision for an early delivery was made, due to concerns about the blood supply to one of the fetuses. The couple, who have two older sons, celebrated Mother’s Day on May 12 with their now six children.
Questions of Coincidence
New York Times writer, Peter Coy (Reference Coy2024), published an intriguing article about the nature of coincidence. He generally dismissed any meaninful connection between the close occurrence of different events; however, he presented the opinions of some experts who feel otherwise. I wrote to him about the striking and more frequent similarities observed in identical twins reared apart, relative to fraternal twins, making the case for genetic underpinnings. I also attached one of my recent papers in which I addressed identical twin ‘coincidence’ with reference to the psychological literature (Segal, Reference Segal2022). Coy requested permission to reprint my letter, albeit in a form that was considerably reduced in length. I have reprinted the final version below:
I specialize in twin studies. Identical twins display more ‘coincidences’ than fraternal twins. The rarer the behavior, the more likely it is to signify a meaningful connection that is likely to partly reflect genetic underpinnings. For example, one pair of identical twins raised apart met at age 25. Both twins used a rare Swedish toothpaste called Vademecm. (Segal, Reference Segal2024)
Reared-Apart Twin Valedictorians
In 2017, I reunited identical 10-year-old Chinese twins, Audrey Doering and Gracie Rainsberry. The reunion actually took place live on the set of ABC’s talk show, Good Morning America. The two girls hugged and cried in a heartwarming moment. Born in China, the twins had been separately adopted by families living in Wisconsin (Audrey) and Washington (Gracie). The twins quickly became close friends and both were recognized as valedictorians in their respective high schools (Najib & Lantz, Reference Najib and Lantz2024). Audrey will attend Vanderbilt University and Gracie will attend Eastern Oregon University.
