We’ve heard it all so many times before: humans with an XY pair of sex chromosomes are male and those with an XX pair are female. Sexual Characters is a series of brief articles on how things are slightly more complicated.
X is for girls, Y is for boys?
For a significant period of time, the X chromosome was thought – and taught – to contain female characteristics and was therefore associated with culturally female-typical traits and behaviors.
The science behind this?
Simply that only “men” had Y chromosomes, so by exclusion, X meant female. Never mind that men also have an X chromosome, which, by the logic above, raises questions concerning the definition of all things manly.
Although genetics is no longer taught this way, the association between the Y chromosome and stereotypically male behaviors and that between the X chromosome and stereotypically female behaviors persists.
So if Y equals male, then do two Y’s make one super male?
XYY
Perhaps 1 in a 1,000 male births result in a person carrying an X and two Y chromosomes – XYY. The actual number could be different, as many people will not know that they have this karyotype.
Features of this syndrome, sometimes called Jacobs Syndrome, include:
- taller than average height
- low muscle tone, or muscle weakness (called hypotonia)
- very curved pinky finger (called clinodactyly)
- widely spaced eyes (called hypertelorism)
- acne during adolescence
- some XYY carriers experience learning disabilities, delayed speech and language skills and emotional difficulties
The final point above deserves emphasis because cognitive disabilities carry social stigmas and although they can occur more often in XYY carriers than among XY folk, Kaiser Permanente, a large health provider consortium, estimates that 88% of XYY people are unaware of their condition because they have no problematic symptoms.
Since its discovery, the XYY karyotype has been a focus of bad science, media sensationalism and politicization. The story begins with a man and his daughters.
XYY Makes Headlines
The XYY karyotype first made news in the English medical journal Lancet in 1961 (paywall). American researchers looking into the reason for a man’s “mongoloid” (a fortunately antiquated term for Down syndrome) daughters discovered that he carried an extra Y chromosome. Although this failed to explain the reason for his daughters’ physical and mental handicaps, they nonetheless assumed a connection.
Two weeks before the article in the Lancet and half a world away, Robert Peter Tait broke into an old woman’s home in Melbourne, Australia, seeking money to rob. In the process, he ended up beating the woman to death. He is then reported to have dressed in her undergarments and to have “subjected her body to certain bizarre sexual indignities.”
Death by hanging was then the mandatory punishment for murder in Victoria and Tait was convicted and duly sentenced.
Legal punishment until 1967. Source: National Library of Australia 
The last man hung in Oz. Source: UK Indymedia
For years leading up to this, many Australians had been advocating an end to the death penalty. Their efforts had contributed to an informal custom within the court system, of commuting death sentences to life in prison. When the court announced that it would not commute Tait’s sentence, the abolitionists launched a vigorous campaign on Tait’s behalf.
In the end, the abolitionists convinced the court to commute Tait’s sentence and five years later, a chromosome survey in the Pentridge Prison where he was held, revealed that Tait carried two Y chromosomes.
According to the prison psychiatrist who attended Tait, had Tait’s chromosomal abnormality been known to the court, his sentence likely would have been commuted easily and with little fuss.
But why?
When You Assume…
An assumption among both biologists and the general public of that era was that things that defined males, such as aggressive tendencies, could be traced to the Y chromosome.
The science meant to support this claim was rather shaky, based upon the reasoning that men were more aggressive than women and only men had a Y chromosome, therefore the Y chromosome carried the trait for aggression.
By this reasoning, twice the Y chromosomes should lead to twice the aggression. And because this was a genetic condition outside the control of the XYY male, courts should give them special consideration during sentencing. At least in Australia, in fact, the XYY syndrome fell under the legal definition of insanity.
In other words, an extra dose of masculinity made one insane.
Very Bad Science
This led Dr. Patricia Jacobs to conduct a chromosome survey of prisoners in the State Hospital at Carstairs, in Lancashire, Scotland, in 1968. Carstairs was a maximum security mental hospital and although not associated with the prison system, it housed some 342 male patients, who had been sent to the hospital by courts, from penal institutions, or from other mental institutions. In all but ten cases, patients at Carstairs had criminal records.
Dr. Jacobs asked if the XYY karyotype was more common in these patients than in the general population. Her study, published in The Annals of Human Genetics in May of 1968, concluded that more men in the hospital had the XYY karyotype than the general public and that this established a positive link between the extra Y chromosome and criminality.
There are some major problems with this. First, by sampling the chromosomes of those already convicted of crimes and/or known to be aggressive, any instance of the extra Y chromosome becomes linked to such behavior. That is, the study creates its own conclusion, like a self-fulfilling prophecy.
Second, the study design leaves out an important class of data: the proportion of XYY men not found in a criminal population have criminal and/or violent histories. Without answering this question, Jacobs’s result was incomplete and one-sided.
Unfortunately, Jacobs was not the only one to let this question slide. The media latched onto her study as well, using it to illustrate a scientific basis for male aggression.
Sensational Media
At the time that Jacobs was conducting her survey, a murder trial was rocking the United States.
In 1966, Richard Speck broke into a Chicago townhouse and murdered eight nursing students with a knife. Amidst media fervor, he was tried, found guilty after a mere 49 minutes of jury deliberation and sentenced to execution.
The ink was still wet on Jacobs’s scientific report during Speck’s trial and people wasted no time in drawing links between the two. Eric Engel, a Swiss endocrinologist, suggested to Speck’s lawyer, that Speck be tested for the XYY karyotype. He based this advice on Speck’s height and on Jacobs’s now discredited theory.
The New York Times ran a three-part series on the XYY karyotype, citing other instances wherein it featured in criminal trials, such as that of Tait in Australia, and of Daniel Hugon (pdf), in Paris. Despite the science linking XYY men to violent crime was still new, to say the least, the Times portrayed it as established fact. Other large and reputable news sources quickly picked up and amplified the story, as well.
Throughout the media frenzy, Speck’s chromosomes underwent multiple rounds of tests. He was first declared XYY-positive, although that finding was soon reversed. Those responsible for the first test later testified that they had never found abnormal chromosomes in the first place.
Nonetheless, a fierce and lasting negative stereotype of the XYY male grew fixed in the public imagination.
The Born Criminal
One reason that this stereotype was so strong and has persisted into recent years, with numerous cameos on popular crime series and movies, is that it reinforces the idea of the Born Criminal.
Sketches from Cesare Lambroso, a big proponent of the born criminal. Sources: Danny Boston & Wikipedia
If crime can be traced to a genetic source, then we can stop it in its tracks through simple genetic screening. It’s nature over nurture and by this logic, some people are just born bad. In a word, this is eugenics.
Enthusiasts of eugenics find the idea of the born criminal attractive, as it reinforces notions of “improving” humanity through selective breeding and culling.
It is important to note that selective breeding is already humanity’s norm (you choose your dates…I hope) and that selective culling is best represented by the Holocaust.
Images from eugenics propaganda. Sources: All That’s Interesting, Camilo Rey & FEE
Leaving the ethics and morality of eugenics to the side, the only way for such a genetic screen to work would be to have a complete molecular understanding of the biology of crime and for that knowledge to be completely correct. Given the challenges we still face in understanding the genetics of height, it is possible that such a goal will never be obtained.
The pseudoscience of born criminals opens the door to, say, linking crime rates in brown-skinned countries to a genetic tendency towards crime and using that as a basis for discrimination. If you do subscribe to this belief, you’ll find ready support among white nationalists.
Fortunately, many modern justice systems do not uphold the idea that one can be born a criminal, hence the widespread presumption of innocence. Nonetheless, the myth of criminal genetic determinism and even of the XYY criminal remains strong enough that, as recently as 2012, a study on the topic was deemed necessary. The report was published in the British Medical Journal, which concluded that one’s socioeconomic situation was a better predictor of male criminality than whether one had the XY, XXY, or XYY karyotype.
The XYY karyotype got off to a bad foot. From its initial association with Down syndrome, to one with criminality, to eugenics and further pop culture criminal spectacle, that extra Y chromosome can’t seem to shake a bad image.
It’s hard to overstate the effect that the Carstairs hospital survey had on this image. By evaluating what proportion of criminals do carry the XYY karyotype, but not asking what proportion of XYY carriers aren’t criminals, both the negative stereotype of the XYY male and the idea of the born criminal were given scientific credentials.
Doing good science can be hard, but publishing bad science can be disastrous.