Twin Conferences Come in Pairs: Views from Brazil
Brazil is a nation rich with twins and twin researchers. In June 2026, I attended two symposia on a range of twin-related topics — the first at the State University of Londrina, in the state of Paraná, and the second at the University of São Paulo (USP), in the state of São Paulo. The first meeting was hosted by Dr Maria Elizabeth Barreto Tavares dos Reis, a faculty member in the Department of Psychology and Psychoanalysis, in Londrina. The second meeting was hosted by Dr Emma Otta, a faculty member in the Department of Experimental Psychology, at the Universidade de São Paulo in São Paulo.
I met Dr Barreto Tavares dos Reis at the International Twin Congress in Assisi, Italy, in 2024. She received her doctoral degree in 2007 at the University of São Paulo — her dissertation was titled Triangular Situations in Twins During the First Year of Life: Conjectures on the Oedipus Complex. She is also the author of a book titled Twin Babies: Emotional Relationship and Parental Care (Bebé Gêmos; Barreto Tavares dos Reis, Reference Barreto Tavares dos Reis2015), and a recently published paper on emotional and cognitive issues concerning an 11-year-old triplet (Barreto Tavares dos Reis & Santos, Reference Barreto Tavares dos Reis and Santos2026). Dr Barreto Tavares dos Reis has also conducted numerous clinics and workshops on the care and rearing of twins. In addition to her scholarship, she is the mother of identical twin daughters, shown in Figure 1.
Dr Maria Elizabeth Baretta Tavares dos Reis (center) with her identical twin daughters, Leticia (left) and Marina (right). Photo courtesy: Dr. Maria Elizabeth Baretta Tavares dos Reis; Photo credit: Guest at a Party, January 1, 2026.
The two-day event, Twins: Science, Fascination and Care, included meetings with students, poster presentations, talks by faculty members representing different department across campus, and a viewing of the 2024 film, The Accidental Twins. The Accidental Twins documents the separation, reunion, and aftermath involving two switched-at-birth identical male twin pairs from Colombia; I wrote about these twins in a 2018 book (Segal & Montoya, Reference Segal and Montoya2018). An excerpt of the film was presented by director, Alessandro Angulo, at the Assisi twin congress. The faculty talks included two round tables, one on caring for twins and their families at the psychological clinic, and the other on care and attention directed toward twin families and schooling. There was also a discussion of embryological aspects of twinning. I presented a talk titled ‘Twins: The Science and the Fascination’, which reviewed twin research methods, findings, and challenges.
The talks in Londrina were delivered in Portuguese, so it is not possible for me to summarize them here. (Two translators were present to assist me verbally but note-taking was precluded.) However, I can discuss several talks. Dr Barreto Tavares dos Reis described an ongoing study involving brief psychoanalytic psychotherapy sessions for twins and their family members. Preliminary findings indicate issues regarding separation and individuation, as well as competition between co-twins. Pregnancy complications requiring hospitalization and a high incidence of premature births — in addition to extreme difficulties in caring for twins, particularly during childhood and adolescence — were indicated.
I also received a translation of a presentation from Professor Silvia Cristiane Murari, in the Department of General Psychology and Behavior Analysis. Her talk was titled ‘Heredity and Environment in the Constitution of Behavioral Repertories: A Behavioral-Analytic Perspective’, given in a round table session. The issue that Professor Murari addressed was how different histories (evolutionary, cultural, and learning) interact in producing behavior. She correctly noted that even genetically identical (MZ) twins do not experience the same environments in the same way. She explained that at school Twin 1 may be asked a question that would be easily answered by both twins; however, by responding, Twin 1 would be inspired to participate frequently in the future. Later, Twin 2 might be asked a question that neither twin could answer and would, consequently, participate less frequently in future settings. These small differences — ‘microinteractions’ — may accumulate over time, mandating respect for the uniqueness of each twin. I concur with the presenter’s conclusion that: ‘… caring for twins means making it possible to have belonging without fusion, closeness without erasure, and connection without the loss of individuality’. The conference proceedings will be published at a future date.
Dr Barreto Tavares dos Reis escorted me on a tour of her campus. We stopped for a visit at the university’s zoology museum. Among the exhibits, shown to us by Professor João Zequi, was a model of a nine-banded armadillo, pictured in Figure 2 — armadillos are known for always delivering MZ quadruplets. These armadillos have a kite-shaped uterus with one implantation site — twinning may have evolved to overcome the restriction imposed by the uterine shape. Interestingly, the seven-banded armadillo can produce between 7 and 15 identical offspring in one pregnancy (Segal, Reference Segal2000, and references therein.)
Nine-banded armadillo, on display at the Museum of Zoology, located at the Center for Biological Sciences, at the State University of Londrina. Photo credit: Dr Nancy L. Segal.
Dr Emma Otta received an MD (1979) and PhD (1984) at the University of São Paulo. She is a Professor of Human Ethology in the Department of Experimental Psychology, Institute of Psychology, at the University of São Paulo. Dr Otta has launched the university’s Twin Panel, an impressive undertaking that is yielding scores of books and publications and is attracting considerable attention to twin research in Brazil; see for example Otta et al. (Reference Otta, Fernandez, Bueno, dos Leandro, Segal, Lucci, Ferreira, Cesar, David, Tatit, Short, Fernandes, Crispim, Moretto, Andrade, Corte, Tobo, Barrichello, de Sousa and Ribeiro2019), Otta and Lucci (Reference Otta and Lucci2021), and Crosato et al. (Reference Crosato, de Lourdes Brizot, Araujo, De Paula, Monticelli, de Resende, Carvalho, Carvalho, Fridman, Mendes, Fraga, Silva, Martinho, Segal, Esseily, Lucci, Prist, Possani, Peixoto and Otta2026). The USP Twin Panel lists over 10 national and international research partners. Several Twin Panel associates (Dr Tania Kiehl Lucci and student Jennifer Leao Correia) have received research honors from the International Society for Human Ethology. I have been a consultant and collaborator on Brazilian twin projects since 2016, following discussions with Dr Otta.
The São Paulo conference, Twins as Windows into Development: Connecting Behavior and Health, lasted for two days, covering a myriad of topics. The first morning session included presentations on the history and progress of the University of São Paulo’s Twin Panel, on how twin studies help us understand environmental effects on mental health, on twin pregnancies, and on early twin development. The afternoon session covered methodological and analytical challenges in twin studies, the impact of membership in an identical twin pair (delivered by MZ twin doctors), facial expressivity and vocal patterns, and mechanisms of social learning. A poster session followed.
The second conference day began with talks on crying and communication, twins’ responses to dental visits, understanding heritability, and twins’ insights into genetic and molecular biological events linked to human development. The afternoon session included presentations on psychological support during twin pregnancy, and journalistic, cultural, and educational perspectives on reared-apart twins. I delivered a talk covering lessons from studies of twins raised apart. The last two talks were especially timely because I had learned of a new separated MZ female twin pair living in Brazil — a Brazilian student attending my talk at the 2026 Western Psychological Association, in Tacoma, Washington, informed me that she had lived next door to one member of the pair. The student facilitated my contact with the twins, and I am now collaborating with USP Twin Panel staff on a detailed case report. A group photo is shown in Figure 3.
Group photo of presenters and attendees at the two-day twin conference, at the University of São Paulo. Photo credit: University of São Paulo Twin Panel Staff.
Summarizing the vast quantity of information presented is not possible given the constraints of journal space. Therefore, I will focus on a book that was discussed by several of its contributors. The conference closed with the distribution of a novel book titled A historia de Tomaz y Gabriel contada por Cordeiro de Sá [The story of Tomaz and Gabriel, told by Cordeiro de Sá] (Monticelli, Reference Monticelli2024, as cited in Costa, Reference Costa2025). The story of these separated identical twins is revealed in a series of comic sketches. A clever feature of this volume is that one twin’s story is told in one half of the book — then readers flip the book to see the other twin’s story. Commenting on this work was Professor Ana Favaretto, an art teacher and cultural producer. She noted that the book has been very effective with children plagued by literacy problems — in fact, the children were inspired to produce similar books about stars.
The book was organized by Professor Patrícia Ferreira Monticelli of the Faculty of Philosophy, Sciences and Letters of Ribeirão Preto. However, many people were involved in writing and production. At the conference, we heard from Dr Ricardo Prist (Institute of Psychology-USP), Dr Wanise Martinez (Institute of Psychology-USP), Professor Cordeiro de Sá (visual artist and cultural producer), and Professor Claudio Possani (Institute of Mathematics-USP), in addition to Prof. Favaretto. Both book covers are reproduced in Figure 4. Additional information about this volume can be found at Costa (Reference Costa2025).
The two covers of the book, A historia de Tomaz y Gabriel contada por Cordeiro de Sá. Photo credit: University of São Paulo images and author Claudia Costa.
Twin Research Summaries
Discordant Transgenderism in African Twins
A life history interview with twin, Vuyo, regarding his male identity and transition to manhood, with reference to the practices of his traditional Xhosa culture in South Africa, is a fascinating and informative contribution to the literature (Ngcofe et al., Reference Ngcofe, Brown and Siswana2026). Vuyo was born as the female member of an opposite-sex twin pair. His early childhood was essentially gender-free — he and his twin were dressed in the same clothes and carried identical backpacks. The situation changed in middle school when he was expected to wear dresses and carry a pink backpack, both of which he disliked. Other than school, he was free to dress as he wished and wore jeans because, as he explained, jeans ‘made me feel that I am the boy that I am’.
When Vuyo’s first-born co-twin eventually underwent the ritual of moving from boyhood to manhood (circumcision, isolation on a mountain, and acquisition of new knowledge), as the second-born twin, Vuyo was expected to go through the same customs as his first-born twin — to Vuyo, this was tantamount to affirming his maleness. Instead of circumcision, his t-shirt was cut; however, this practice did not recognize him as a male. At this point in the ritual process, he had to separate from his twin; but continued carrying out the ritual as a twin. Some years later, Vuyo’s brother was killed in an accident — following the funeral, his family allowed him certain privileges that are reserved for males and treated him as such. Interested individuals are encouraged to review the lengthy text in full.
Attachment in Twin Families
The Strange Situation Procedure (SSP), developed by Ainsworth et al. (Reference Ainsworth, Blehar, Waters and Wall1978), is a simple but insightful experimental means for assessing the quality of infants’ attachment to their mother. Over the course of eight scenarios that last approximately 20 minutes in total, infants are observed when their mothers leave the playroom, and strangers enter. Ainsworth identified three attachment categories: secure, insecure-avoidant, and insecure-resistant; a fourth category (disorganized-disoriented) was added later by Main and Solomon (Reference Main, Solomon, Yogman and Brazelton1986).
A novel study by van Rijn-van Gelderen and colleagues (Reference van Rijn-van Gelderen, Ellis-Davies, Vecho, Rubio, Carone, Frau, Schiavetto, Runze, Jorgensen, Bos and Lamb2025) compared attachment quality in families created by assisted reproductive technology (ART). Participants were from the United Kingdom, the Netherlands, and France, and included same-sex and opposite-sex couples — among the children were 16 pairs of twins. Twins represented 37.5% percent of the 48 same-sex male partners, 4.3% of the 93 same-sex female partners, and 13.3% of the 57 opposite-sex partners. Significant differences among family type in quality of attachment were not found, although children from the Netherlands were more likely to be classified as secure, and same-sex male couples were more likely to have had twins than same-sex female couples. It is unfortunate that the attachment qualities of the twins were not described separately.
Twins have, however, been used creatively in other attachment-related studies. For example, Vandell et al (Reference Vandell, Owen, Wilson and Henderson1988) found that by age 24 months twins were more likely to interact with their co-twin than with an unfamiliar peer. Gottfried at al. (1994) compared the behaviors of 15 twin pairs under several conditions: (1) mother and twins present; (2) twins together, mother absent; (3) target twin isolated from co-twin and mother. Twins’ upset was minimal when separated from their mother when the co-twin was present. In contrast, separation from the mother and co-twin resulted in a high level of distress for the isolated target twin. Unfortunately, neither of these analyses examined their findings with reference to zygosity.
Tactile Sensitivity in Twins
Tactile sensitivity is the capacity to perceive information that is external to the body. Researchers in Japan examined tactile sensitivity in a sample of 25 MZ twin pairs to identify health conditions and other factors associated with this trait (Sakaguchi et al., Reference Sakaguchi, Morito, Konyo, Sakata, Akada, Watanabe, Sakai and Hara2026). Using only MZ twins, classified as such by DNA analysis, they controlled for genetic differences — thus, within-pair variation could then be linked to nongenetic factors. Tactile sensitivity was assessed by twins’ responses to suction stimuli on the cheek, psychophysiological measures, and questionnaires. Eighteen pairs obtained similar sensitivity thresholds, demonstrating genetic effects. In contrast, differences were detected in seven pairs — in these pairs, reduced tactile sensitivity was linked to greater physical and mental disorders; for example, fatigue and anxiety. Thus, genetic factors, as well as health conditions and lifestyle practices appear to affect tactile sensitivity.
Self-Employed Twins and Stress
An interdisciplinary team of researchers utilized a natural co-twin control study to assess relationships between self-employment and psychological stress (Souitaris et al., Reference Souitaris, Nicolaou, Waters, Shepherd and Hashem2026). MZ twins drawn from Finland provided their level of perceived stress, whereas stress experienced by twins from the United States was obtained via psychophysiological measures (daily cortisol levels). Twins in both samples showed that self-employment was associated with greater stress. Controlling for selection effects (self-selection into an entrepreneurial career) reduced this association, although it remained meaningful. In addition, long working hours mediated the relationship between self-employment and stress.
Note on Chimerism
In one of my previous News, Views, and Comments column (Segal, Reference Segal2026), I cited a reference indicating a relationship between dizygotic (DZ) twinning and chimerism (Leach, Reference Leach2026). Other reports of chimerism in DZ twins have appeared, although not all have compared its presence in different subject samples (Dziegiel et al., Reference Dziegiel, Hansen, Haedersdal, Barrett, Rieneck, Main, Hansen and Clausen2017). Subsequent to the publication of that article, I received a research report showing a lack of such an association (Johnson et al., Reference Johnson, Peters, Lambalk, Dolan, Willemsen, Ligthart, Mijatovic, Hottenga, Ehli and Boomsma2021). Readers may wish to examine and compare the various papers.
Human Interest Items
Artistic Twinships
Two pairs of artistic twins are gaining attention. Fraternal male twins, Simon and Nikolai Haas, from Austin, Texas, now 41 years of age, have been creating art since the age of 15 (New York Times, 2026). When they were in their twenties, they received a commission from Italian designer Donatella Versace that greatly furthered their career. Currently, the two have opened an exhibition titled ‘Haas Brothers: Uncanny Valley’ at New York’s Museum of Arts and Design. Their goal is to make objects that offer viewers an ‘alternative experience’, drawing them into a whole new world. Artistic creativity runs in their family — their older brother was a childhood actor, their father was a stone carver and painter, and their mother is an opera singer and screenwriter. Little information was given as to how the Haas twins work together — this is unfortunate, as there seem to be fewer fraternal than identical twin collaborators, and knowing their creative process would be insightful (Segal, Reference Segalin press).
Another artistic pair worth noting are identical twins, Anna and Elena Balbusso (Heller, Reference Heller2026). The two describe their collaboration as ‘symbiotic’ — that is, they ‘melt into a single multi-creative entity’. These Italian twins have had previous shows but are currently having their first New York exhibit at the Society of Illustrators. They decided to work together to avoid within-pair competition. Their process involves continually talking to one another — they explain that illustrators are encouraged to follow the same style to gain recognition, but they prefer flexibility, integrating elements from different languages and cultures. They also work on socially sensitive and timely topics, such as civil rights, abortion, and violence against women. The twins summarized the nature of their relationship as follows: ‘We see and feel ourselves as different people, but we have always felt like twins. Being twins is an ancestral bond of deep love, maybe even stronger than the bond between a mother and child. It is a condition where “we” comes before “I”.’
Note: The twin type of both pairs was indicated by the twins and confirmed by me from photographs.
Naturally Conceived Identical Quadruplets
In July 2026, a set of identical female quadruplets was delivered to Jenitar Na’amoana and her partner Jortham, in Brisbane, Australia (Miles, Reference Miles2026). The quads — Emily, Harriet, Alexa, and Catherine — were born healthy at 28 weeks and four days gestation. Their birth weights ranged from 1025 to 1151 grams (2.25 to 2.54 pounds). The four infants had shared a placenta while in the womb. The couple already had four children between the ages of 1 and 10 years and had not planned on having a fifth baby — the birth of the quadruplets nearly doubled the size of their family. The parents have established a GoFundMe page to defray the rising costs of raising eight young children.
Sports Award for a Deceased Co-Twin
In July 2026, twin Jarron Collins accepted a trophy (Arthur Ashe Awar for Courage) from ESPYS (Excellence in Sports Performance Yearly Awards) on behalf of his deceased twin brother, Jason (Giacomazzo, Reference Giacomazzo2026). Jason, the first openly gay player for the National Basketball Association (NBA), passed away from glioblastoma at age 47. The twins appear to be identical, based on inspection of photographs. Jarron is a professional coach and former basketball player (National Basketball Coaches Association, 2026). He uttered these words about his twin brother: ‘The courage he showed and the way he moved in this world truly made him a trailblazer, an inspiration to so many others, and his impact will be remembered.’
New Prenatal Procedure Saves Twins’ Lives
Twins in Great Britain were the first pair to receive a prenatal noninvasive treatment for twin-to-twin transfusion syndrome or TTTS (Roxby, Reference Roxby2026). The twins, Nancy and Margo Garrett, were among the 10−15% of identical twins to be affected by an imbalance in their blood flow — the recipient twin received blood prenatally from their donor co-twin, creating size discrepancies and endangering both twins. Using highly focused ultrasound, the procedure blocks blood flow in 90% of the blood vessels. The twins were born healthy at 34 weeks gestation with weights that were better than expected — Nancy weighed 3 pounds 7 ounces, while Margo weighed 3 pounds, 3 ounces. The twins, now 4 years old, will begin preschool shortly.
World’s Most Premature Twins
Opposite-sex twins Adia Laelynn and Adrial Luka Nadarajah, of Canada, celebrated their fourth birthday on March 4, 2026 (RighttoLife News, 2026). Guinness World Records (2026) has recognized them as the world’s most premature twins. They were born at 22 weeks, or 126 days prior to the date they were due. The twins were not expected to survive — their combined birth weight was 750 grams or 1.65 pounds. They remained in the Neonatal Intensive Care Unit for 6 months until doctors felt they were ready to be released. So far, they have achieved their developmental milestones on schedule.
