The 18th International Society for Twin Studies convention took place between June 15−17, 2023, in Budapest, Hungary. A selective sampling of highlights from the meeting are presented. This is followed by a brief overview of ongoing twin research at the University of Aberystwyth in Wales and some twin treasures in the National Library. Next, reviews of timely research that examine temperamental similarities and twin relations, the maximization of twin research designs, a rare ectopic twin pregnancy, and twins’ academic self-concept formation are presented. The final section covers stories appearing in various media sources that are informative, enlightening, and interesting, namely a reunion of identical infant twins, the birth of identical-fraternal quadruplets, identical twin comedians, meeting an unrelated look-alike, and twins in the Tour de France.

Twins’ memoirs and autobiographies both enlighten and entertain. These works, often overlooked by researchers, may suggest new avenues for investigation, such as nonshared environmental events that propel twins in different directions. Of course, MZ twins’ generally parallel experiences and DZ twins generally criss-crossing paths are the bases of fascinating life stories. The following sections examined recent research on fetal reduction in twin pregnancy, twins’ personality and military service, growth restriction in twins, and advances in conjoined twin separation. This article closes with reports of a scientist who performed gene editing on twins, a twin conception from 33-year-old embryos, twins’ physical outcomes from dietary differences, fraternal twins with the world’s largest height difference and the Twin Home Experts who conquer rat infestation in New York.

Waardenburg’s syndrome involves deafness accompanied by various visual difficulties. The role of twins in identifying this disorder and advancing understanding of its origins and symptoms is described, beginning in 1916 and continuing to the present. This overview is followed by current research on monozygotic (MZ) twins’ different dermatoglyphic features, twins with sagittal suture crainosynostosis, blood pressure in female twins, and MZ twins’ education and political knowledge. The final section presents media reports describing controversies surrounding twins created by reciprocal in vitro fertilization, reared-apart triplets’ limited TV series, abducted twin infants, the Winkelvoss twins’ charges by the Securities and Exchange Commission, and going from ‘Me’ to ‘We’.

The experience of going through the personal library of our late esteemed twin research colleague, Dr Irving I. Gottesman, is described. I came away with fond memories and unexpected treasures. This essay is followed by brief reviews of timely research on factors affecting callous-unemotional traits, depressive symptoms in prospective Chinese twin mothers, twins with sagittal suture craniosynostosis, and creative expressiveness and educational achievement. Media reports on informative topics of interest to researchers and the general public include male-female twin Holocaust survivors, nontuplets born in Mali, Indian twins who married the same man, twins born from the longest frozen embryos, an infant twin abduction and twins born in different years.

Quadruplets are at elevated physical risks at prenatal, perinatal, and postnatal levels, relative to twins. A brief review of this area is followed by discussion of a female quadruplet with three co-quadruplet brothers. Next, several timely twin research reports are examined. The topics include antenatal corticosteroids and twins’ neonatal outcomes, the meaning of fatherhood in families with twins, what doppelgängers (look-alikes) reveal about physical and behavioral similarity, and monozygotic (MZ) co-twin discordance for asymmetric pigmented paravenous chorioretinal atrophy. A lawsuit involving alleged cheating on a medical school examination by identical twins is also reviewed. General interest stories cover opposite-sex twin Holocaust survivors, twin models at a Gucci fashion show, twins with different fathers, reunited female twins who entered the same convent, the death of an MZ female twin soldier during training, and the surgical separation of conjoined twins in Brazil.

The unique sources of artistic inspiration and talent of twin artists are examined. The professional literature is rich with twin studies of creativity, but lacking when it comes to specific artistic domains — for example, painting and sculpting. The section that follows provides reviews of current research on ethnic and racial factors affecting type of twin delivery, pregnancy outcomes when twins are conceived naturally or with reproductive assistance, the effects of intrauterine growth discordance on the timing of twin delivery, and three-dimensional (3D) assessment of twins’ facial resemblance. The final section summarizes information about twins in the media. The stories include twins distinguished for both baseball playing and physical injuries, twins who reached the National College Athletic Association’s Elite 8, a twin pair’s grave and epitaph, a mother who conceived twins three times in 2 years, twins in the Hockey Hall of Fame, and a set of superfetated twins.

The focus of this article is on insights gained from the extraordinary dynamics that took place between a pair of reunited monozygotic female twins from Greece. Topics include visualizing the co-twin prior to meeting, the unique love and attraction between the twins, a mother’s response to discovering her child’s cotwin and the challenges posed by insufficient kinship categories. The following section of this article surveys four recent twin research reports. They include Bereavement and Lifespan Associations; Novel Mutations in Twins; Parenting Premature Multiples; and Conjoined Twins. The final part of this article presents interesting and informative news about twins from popular sources. The topics covered are the passing of Madeline Albright (Secretary of State and mother of twins); identical twin songwriters; visually impaired twin and sibling skiiers; identical twin brothers who both received heart transplants; and the naming of the Genain quadruplets.

Twin research proceeds at a rapid pace, with new findings constantly modifying our knowledge and thoughts about many issues. In the present article, this concept is applied to the writing of books and articles about twins, with special emphasis on the author’s recent experience. My lead essay in most contributions to the News, Views and Comment section of this journal is usually followed by a review of current research findings; however, significant events necessitated a departure from this format. At this time, it is important to both honor and remember colleagues and twins, both past and present. The final entry in this article highlights media events that variously pose biological and social implications for our field. They include the hardships of Ukrainian twins during wartime; twins born in different years; identical twin surrogacy, a quaternary family and abducted twins in Serbia.

Selected highlights from the 2021 Congress of the International Society for Twin Studies are reviewed. The perspectives of a new graduate student member to the society are also included. Timely research covering issues related to maternal bonding with twins, twins with Peters anomaly, selective termination in dichorionic twin pairs and neuropsychological functioning in twins with neurofibromatosis is reviewed. The final part of this article includes interesting and informative media reports related to the world’s most premature survivor who is a twin, identical male baseball players, Malaysian twins switched at birth and a pair of the so-called ‘biracial’ twins.

The processes that give rise to monozygotic (MZ) twins remain elusive. This article describes various theories of MZ twinning that have been examined over the years, although they continue to be speculative. It has also been impossible to know if a singleton began life as an MZ twin; however, a critical technological breakthrough can now reveal this important birth history information with a high degree of certainty. The section that follows presents reviews of current research regarding rare twin loss, development of a twin registry, twins’ communicative delays and DNA testing for vanishing twins. The article concludes with a survey of newsworthy twins, namely identical twins discordant for COVID vaccination, the world’s oldest identical twins, an Olympic athletic stand-in and fraternal twin football players.

Craniosynostosis involves the early closure of one or more joints connecting the bones of an infant’s skull. A case of young monozygotic (MZ) male twins with an unidentified variant of this condition is described, followed by a summary of relevant published reports. This overview is followed by descriptions of a kangaroo care program for premature twins, developmental delay in an MZ twin pair, osteosarcoma in one MZ twin and controversial issues in the management of multiple pregnancies. Media reports of twin and triplet Olympic athletes, a twin’s rescue from a crocodile, the birth of twin pandas in Japan, a case of twin surrogacy and the birth of identical triplets are also presented.

Every reared-apart monozygotic (MZ) twin pair offers a fresh perspective on human developmental questions. This is true regardless of whether the co-twins were raised in the same country or across the globe. The members of two pairs of separated MZ female twins have recently come to attention. In one case the twins were raised by different families in Argentina; in the other case the twins were raised by different families in Sweden and Vietnam. The perceptions and perspectives of these twins are insightful. The twin research section that follows begins with a tribute to our late esteemed colleague, Dr Isaac Blickstein (1953−2020). Research concerning the infanticide and sacrifice of Archaic-aged twins and triplets and prehistoric twin burials is reviewed next. Highlights from a conference focused on the 2018 film Three Identical Strangers are also included in this portion. The final section of this article includes media reports of an atypical twin father, an actor’s twin brother, a twin link to the 1921 Tulsa, Oklahoma massacre, the birth of superfetated twins, twin comedians and script writers and Indian twins’ tragic loss to COVID-19.

A greater frequency of left-handedness among males than females has been observed in general populations. Past studies have explained this difference with reference to males’ greater susceptibility to adverse birth events, while more recent studies have identified other contributing factors. On January 16, 2020, U.S. senators signed an oath to act impartially during the president’s impeachment trial. This televised event allowed direct comparison of the proportion of right-handedness and left-handedness in a professionally accomplished sample of males and females. As expected, no sex difference in the proportion of left-handed senators was found, although the small sample size offered low statistical power. Replicating this finding with a larger sample would support the view that left-handedness among select groups of males is linked to genetic factors.

Selective termination is the term used for the elimination of an abnormal fetus. In contrast, multifetal pregnancy reduction refers to the termination of one or more members of a twin or higher-order multiple birth set, respectively, to reduce the high risks associated with these pregnancies. The procedure can also be used when a serious physical condition is detected prenatally in a member of a multiple birth set. In a minority of cases, selective termination has reduced two healthy fetuses to one when parents wanted just one additional child in the family. In the present article, the perspectives of a surviving twin whose family wished to terminate both healthy fetuses are examined. Next, past and present twin studies of primordial dwarfism, public service motivation, an analytical model, the global twinning rate and germline differences are summarized. The article concludes with a synopsis of twin-related news that covers twins and Dyngus Day, triplets born in an Austrian displaced persons’ camp, the film Superior — about estranged identical twin sisters, a couple adopting their own twins after surrogacy and a new case of twins and primordial dwarfism, a condition introduced in the research reviews.

Modern reproductive technology and revisions of conventional family structures have yielded a curious array of twin-like sibships. Many of these pairings pose the same rearing questions and educational issues for parents and teachers as do ordinary monozygotic and dizygotic twins. This article considers how we classify these sibships, given the important implications for the pair members, their families, their friends and the professionals who care for them. Next, reviews of research on twins’ birth weight and brain development, twinning and vocabulary knowledge, fetal loss in twin pregnancy and twin-family Olympic medal winners are presented. The final topic covers recent media attention to young twin soldiers, a twin-run laundry, a male-female pair’s political differences, a twin-based graphic novel and twin sisters’ deliveries.

Research into the origins of twinning has focused mostly on contributions from the female side of the family. A review of current findings suggests that possible male contributions to twinning events have been overlooked. This section is followed by brief reviews of twin research concerning monozygotic twins discordant for Parkinson’s disease, fetal loss in twin pregnancies following prenatal diagnosis, uterine rupture and repair in an early twin pregnancy and a twin study of affectionate communication. The concluding portion of this article presents human interest stories involving twins that are both informative and poignant, namely conjoined twins in a triplet set, identical twin nurses who delivered identical twins, identical twins discordant for COVID-19 recovery course, identical twins who passed away from COVID-19 and archeological finds of the oldest identical twins.

John C. Loehlin, professor of psychology at the University of Texas, at Austin, passed away on August 9, 2020. John was 94 years of age. He will be remembered for his seminal contributions that have furthered the field of twin research in so many ways. An overview of his career is presented, with fond memories from his son and several colleagues. This tribute is followed by reviews of twin research on cognitive skills and social mobility, risk of subarachnoid hemorrhage, heritability of selected dental traits and twin-to-twin transfusion syndrome. Finally, twin-related topics of human interest include identical twins with different health histories, twins born 97 days apart, retiring twin tennis players, TikTok twins and twin reality stars.

A brief review of research findings regarding twins living apart is presented. This review is followed by a look into the lives of a pair of monozygotic male twins who have lived in different continents for many years, but who stay closely connected. The reasons behind their decision and its impact on their behavioral resemblance and social relationship quality are examined. The next section summarizes recent studies that address the management of monochorionic-diamniotic twin pregnancies, paternity testing in multiple pregnancies, trisomies in twin pregnancies and the roots of resilience. The final portion of this article presents human-interest stories involving reunited Brazilian twins, a new resource for twins with disabled co-twins, twins separated in the Secret of the Nile television series, a new book about Dr Josef Mengele and his horrific twin experiments conducted at the Auschwitz–Birkenau concentration camp, and a pair of twins dedicated to helping others.

It is likely that genetic factors play a role in the susceptibility to, and recovery from, COVID-19. A survey of ongoing twin research could produce findings likely to help in the prevention and management of this pandemic. This survey is followed by a review of research comparing selected features of asthmatic and nonasthmatic twins, links between twin mammals and COVID-19, and relationships between twin delivery and the three ‘Rs’. The final section of this article presents newsworthy twin-related items, some associated with COVID-19. They include a summary of the Rainman Twins film, a study of anal prints, the ‘Twins’ Irish pub, newborn twins ‘Covid and Corona’, the death of a surgeon who separated conjoined twins, and Twinco, a twin-based supply company.

This article describes a 1930s case study series involving dizygotic female twin infants. The twins’ development was evaluated following periods of intentionally restricted practice and minimal social stimulation. In the opinion of the author of the current article, the study is very unsettling and unacceptable, despite the lack of institutional review boards at that time. This discussion is followed by twin research reviews of recent papers concerning twin and non-twin intracytoplasmic sperm injection conceptions, the Emory University Twin Study of cardiac and brain functions, labor trials in multiple pregnancies after previous C-section delivery and cell-free DNA fetal fraction in twin pregnancies. The article concludes with news items of a twin survivor of Auschwitz, a situation in which twins traded places, the rare birth of identical twin foals, the novel delivery of co-twins in different decades and the Twins Ambulette Service.