Issue 2: Historical perspectives on twins and twin research

ISSN: 2652-5518
By Brian Byrne

Main points 

  • Twins feature in the mythology of many ancient cultures
  • The scientific value of twins has been understood for millennia
  • Systematic twin research has a history of nearly 150 years


Twins Research Australia (TRA) has two missions. One is to support and encourage the scientific opportunities afforded by twins and other multiple births to understand the human condition, including the origins and treatment of human diseases and related issues. Its other mission is to support twins themselves and their families through a greater scientific understanding of multiple births and the consequences of growing up a twin. It turns out that both of these missions have long historical roots. In this piece I identify some of those roots. As I explain, the scientific value of twins was appreciated as early as the 4th century CE, and ideas about twinning itself feature in Greek mythology. Thus, the missions of the TRA have their origins in ideas that extend far into the past.

Suggested citation: Byrne, B. Historical perspectives on twins and twin research. Conversations in Twins Research, Twins Research Australia, Melbourne, 2018,

Twins as a source of knowledge

Saint Augustine (354–430) was a fierce opponent of astrology, the belief that our fates are determined by the configurations of the heavens at the time of our birth. In Book V of The City of God, he set about denouncing astrology by citing a series of observations about twins. The twin brothers Esau and Jacob, he wrote, were born “the one so immediately after the other, that the first took hold of the heel of the second.” Nevertheless, he added,

so great a difference existed in their lives and manners, so great a dissimilarity in their actions, so great a difference in their parents’ love for them respectively, that the very contrast between them produced even a mutual hostile antipathy.

The idea, then, that our lives are governed by “the position of the stars which exists at the moment of one’s birth” cannot be sustained. Augustine also invoked

the famous physician Hippocrates [who] has left in writing that he had suspected that a certain pair of brothers were twins, from the fact that they both took ill at once, and their disease advanced to its crisis and subsided in the same time in each of them. Posidonius the Stoic, who was much given to astrology, used to explain the fact by supposing that they had been born and conceived under the same constellation. In this question the conjecture of the physician is by far more worthy to be accepted, and approaches much nearer to credibility, since, according as the parents were affected in body at the time of copulation, so might the first elements of the fœtuses have been affected, so that all that was necessary for their growth and development up till birth having been supplied from the body of the same mother, they might be born with like constitutions. Thereafter, nourished in the same house, on the same kinds of food, where they would have also the same kinds of air, the same locality, the same quality of water … and where they would also be accustomed to the same kinds of exercise, they would have bodily constitutions so similar that they would be similarly affected with sickness at the same time and by the same causes. But, to wish to adduce that particular position of the stars which existed at the time when they were born or conceived as the cause of their being simultaneously affected with sickness, manifests the greatest arrogance…

In the case of Esau and Jacob, the very different twins, Augustine wrote:

Hippocrates would give what is in my opinion the simplest reason, namely, that, through diversity of food and exercise, which arises not from the constitution of the body, but from the inclination of the mind, they may have come to be different from each other in respect of health.

The common theme, then, is that sometimes twins are very different, sometimes very similar, and in neither situation can we call upon an astrological explanation. Indeed, as well as being unnecessary (interestingly, an early instance of Occam’s razor – the principle that the simplest solution tends to be the right one), it would be the height of contradiction to do so. Interesting, too, that in his denunciation of astrology St Augustine was a committed environmentalist, choosing to attribute the similarity in health of Hippocrates’s twins to similarity of environment, from conception to adulthood, with an analogous explanation for twin differences: the “diversity of food and exercise.” These days, health researchers might be more open to a genetic explanation in the case of similarity, one obviously unavailable to the good saint.
In the modern era, Charles Darwin’s cousin Francis Galton, in 1876, published “The history of twins as a criterion of the relative powers of nature and nurture” [1], although Galton did not recognise the critical distinction between mono- and dizygotic twins, which is the workhorse of modern twin research. One of the first actual pieces of research featuring twins was Merriman’s “The intellectual resemblance of twins”, in 1924, showing that identical twins were markedly more similar than fraternal twins [2]. Thus, systematic twin research and its statistical basis have a history of almost a century and a half, and the insight that twins can inform our understanding of the world emerged 1800 years ago. The TRA is therefore an inheritor of a long tradition of vibrant thinking and research, one that it is fostering enthusiastically.

Early ideas about twinning

In Greek mythology, Zeus chose Alcmene, the wife of Amphitryon, as his last earthly mistress. Zeus visited and impregnated Alcmene while Amphitryon was away on a mission of vengeance. When Amphitryon returned he, too, slept with Alcmene, resulting in a second pregnancy, and twins. One was the semi-divine Herakles (Hercules). The idea that twins were the consequence of a woman having intercourse with two men thus gained a foothold in Western thought.
This idea continued to hold sway in early modern Britain. The term used was superfetation, which in the words of Helkiah Crooke (in Microcosmographia, published in 1615) “is nothing else but a second conception, when a woman already with child accompanying a man conceiveth again, as it were a new conception above another before conceived” [3]. Although superfetation (conception in different menstrual cycles), or more often superfecundation (in the same cycle), can occur, it is rare, but the idea that it was the mechanism of twinning led to another misinterpretation, this time of a moral kind. In answer to the question of why a woman would continue to copulate after she has conceived “when Beasts do not”, Nicholas Culpeper (1651) ventured the opinion that

the curse of God for Adam’s first sin lies more heavily upon Man, than it does upon the Beasts, and Lust is a great part if this Curse, and the Propagation of many Children at once an effect of that intemperancy. [4]

Not only were the mothers of twins charged with being sexually excessive, Thomas Browne (1646) suggested that adultery is involved in this supposed double conception. There was not, he wrote, “any absolute securitie in the policy of adultery after conception; for the Matrix, after reception of the proper Tenant, may yet receive a strange and spurious inmate” [5]. Writers of the time saw their ideas as continuous with antiquity, but at least poor Alcmene cannot be seen as the source of the adultery element of the package; Zeus had appeared to her in the form of Amphitryon, her husband.
Some commentators see it as rather odd that Shakespeare ignored the allegedly suspect morality involved in twinning in his depiction of twins in the plays Comedy of Errors and Twelfth Night [6], both of which exploit the identity confusion that twins afford. This, some suggest, may have been because he was the father of twins, Hamnet and Judith, born in 1585, well before he wrote the two plays. It would hardly do to implicitly accuse Anne Hathaway of an adulterous lifestyle.
In ancient mythology, twins often represented the duality of nature, male/female, good/evil, and so on. Apollo and Artemis, the twin children of Zeus (again) and Leto, were ascribed to the sun and moon respectively. Apollo had a variety of jobs, including looking after art and music, as well as health, though he could bring about plagues as well. Artemis, the supreme environmentalist, was the goddess of the hunt, wilderness and childbirth, and was seen as the protector of young girls. The male twins Sahadeva and Nakula in Hindu mythology had distinct roles. Sahadeva was particularly wise, with the handy ability to see the future, but was constrained to be silent about it for fear that his head would split into pieces. Nakula was especially skilled in horse breeding, and was a charmer and therefore a fine diplomat. The Mayan hero twins Hunahpu and Xbalanque were also seen as representing complementary forces – sun and moon, sky and earth, life and death. Other twin gods turn up in Nordic, Egyptian, Syrian and Native American mythologies, among others.


Twins continue to fascinate people today, but mercifully we have an attitude to twins and their parents informed by modern science. Twins Research Australia contributes to this science by conducting research into the unique health concerns of twins and their families and enabling researchers to look for cures for the many disease that afflict us.

About the author

Brian Byrne is an Emeritus Professor in the School Psychology, University of New England, and a member of the ARC Centre of Excellence in Cognition and its Disorders as well as of the NHMRC Centre of Research Excellence in Twin Research. His PhD is from McMaster University, Canada. His research interests have centred on literacy and language development, most recently using data from twins who have sat the Australia-wide NAPLAN tests.


1. Galton, F. The history of twins, as a criterion of the relative powers of nature and nurture. The Journal of the Anthropological Institute of Great Britain and Ireland, 1876. 5:391-406. 
2. Merriman, C. The intellectual resemblance of twins. Psychological Monographs, 1924. 33(5):i-57.
3. Crooke, H. Microcosmographia: A Description of the Body of Man: Together with the Controversies Thereto Belonging. 1615, William Iaggard.
4. Culpeper, N. A Directory for Midwives. 1651, Peter Cole.
5. Browne, T. Pseudoxia Epidemica. 1646, Edward Dod.
6. Shakespeare, W. Mr. William Shakespeares Comedies, Histories and Tragedies [First Folio]. 1623, Isaac Iaggard.