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A fictionalized story of two real sisters sheds light on the darker side of human research

The Less You Know the Sounder You Sleep

Juliet Butler
4th Estate
448 pp.
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In 1959, Tatiana Alexeyeva, a Soviet physiologist, declared conjoined twins to be “objects of great scientific interest. A most remarkable human experiment created by nature.” The twins she would go on to describe were Masha and Dasha Krivoshlyapova, born in Moscow in January 1950. Alexeyeva’s colleagues had assumed care of the girls shortly after their birth, having misled their mother into thinking that they had died of pneumonia.

The Less You Know the Sounder You Sleep is a fictionalized account of the lives of Masha and Dasha, whose childhoods were spent in state-run institutions, where they were subjected to horrific “experiments” performed without their consent. The story is told by Juliet Butler—a journalist and close friend of the girls who collaborated with them on an autobiography in 2000 (1).

Conjoined twins are monozygotic (MZ, or identical) twins born physically joined. They are rare—occurring at a frequency between 1 in 50,000 and 1 in 100,000 live births—are twice as likely to be female, and can take many forms depending on the site of joining.

Masha and Dasha were joined at the hip, shared three legs (one vestigial), and one reproductive system, bladder, and colon. They each had separate spines (conferring distinct nervous systems), as well as separate small intestines, hearts, and lungs. Each girl had a separate head and pair of arms.

Despite their shared anatomy, Masha and Dasha were strikingly different from birth. Masha was the dominant twin, diagnosed in childhood as psychopathic. She would frequently beat Dasha, who was more reserved and empathic. They also differed in intellectual ability, speech, mobility, sleep patterns, and susceptibility to infection.

The book touches on the origins of the pair’s psychological differences, with Dasha recalling having overheard a conversation in which researchers invoked the “split brain theory.” This theory, now discredited, stated that personality differences in twins were due to their preferential use of one hemisphere. Today, differences within MZ pairs are attributed to nonshared environment and to stochastic developmental factors.


The Less You Know the Sounder You Sleep offers a glimpse into the lives of conjoined twins Masha and Dasha Krivoshlyapova, who were subjected to horrific experiments by Soviet scientists during the 1950s.

For the first 6 years of their lives, Masha and Dasha were kept in a glass cage inside a locked room. They were subjected to abhorrent experiments designed to investigate the relationship between their shared immune system and their separate nervous systems. They endured starvation, electrocution, extreme freezing, scalding, and sleep deprivation. Their blood and gastric juices were sampled regularly.

As Butler reveals, the twins found these experiments so traumatizing that they learned to mentally shut down. However, deprived of toys, the girls would sometimes incorporate the tests they were subjected to into role-play games. “Let’s play Gastrics,” 6-year-old Masha says early on in the book. “Nyetooshki. I never get to put the tube down you,” counters Dasha. “Here … Open up. Down we go.”

After spending 6 years in Moscow’s Paediatric Institute, Masha and Dasha were moved to the Scientific National Institute of Prosthetics (SNIP) in Moscow, where they were provided with schooling up to the age of 11. At 14, the girls were transferred to the School for Invalids, Novocherkassk, in what is now southeastern Russia, where they were graded according to their degree of “defectiveness” rather than their academic ability. From the age of 18 until their deaths at age 53, they lived in a series of institutions for veterans.

Butler works in themes of resilience, while highlighting issues surrounding society’s perception of disability. The first time the twins are allowed out of SNIP, for example, a commotion arises, with Moscow residents screaming, “Monster, it’s a monster!” (Naively, the girls look around for a real monster.)

Butler also spends a great deal of time exploring the personal tensions that exist between the two sisters, revealing the fraught nature of their codependent relationship. That such a compassionate tale has been brought forth is a testament to a tenacious author, who spent 15 years helping the twins unpack their story.

The book’s title references a Russian phrase that reflects the notion that the authorities often prefer to keep the masses in the dark. The harrowing story of Masha and Dasha, however, shows that ignorance is far from bliss. Hopefully, the retelling of this story will act as a reminder that the darker side of human research should never be revisited.


  1. J. Butler, Masha und Dasha. Autobiographie eines Siamesischen Zwillingspaars (Scherz Verlag, München, Berlin, 2000).

About the author

The reviewer is at the Murdoch Children’s Research Institute, Royal Children’s Hospital, and the Department of Paediatrics, University of Melbourne, Parkville, Victoria 3052, Australia.