Killer Genes: Do Chromosomes Play A Role In Criminal Behavior?

Over the years, scientists have studied the role that extra chromosomes could potentially play in criminal behavior.

Photo by: Arthur Shawcross [Sullivan Correctional Facility]

Arthur Shawcross [Sullivan Correctional Facility]

By: Catherine Townsend

Francis Heaulme, the serial killer who would later be nicknamed the "Criminal Backpacker," was born in France. Heaulme had a genetic condition called Klinefelter's Syndrome — which meant that he had an extra "X" chromosome — a trait he shares with several other notorious killers.

Humans are born with 46 chromosomes in 23 pairs, and the X and Y chromosomes determine a person's sex. Most women have 23 XX chromosomes and men have 23 XY, making the total number of chromosomes 46.

But according to the World Health Organization, occurring in just a few births per thousand, some individuals will be born with a single sex chromosome (45X or 45Y) and some with three or more sex chromosomes — which results in variations including 47XXX, 47XYY, or 47XXY.

Over the years, scientists have studied the role that extra chromosomes could potentially play in criminal behavior. They have not found a direct link, but a Danish study did find that crimes including sexual abuse, burglary, and arson were significantly increased for XXY men. They attributed this to the "poor socioeconomic conditions related to the chromosome aberrations."

In 2009, researchers found that men with XYY Syndrome are more common in prison populations. In "Introduction to Forensic and Criminal Psychology 3," Dr. Dennis Howitt wrote that he believes that the increased number of XYY men in the offender population could be due to the learning difficulties that can be caused by the condition.

Klinefelter Syndrome / XXY

Klinefelter syndrome is associated with a group of chromosomal disorders in males in which one or more extra X chromosomes are present, which can affect physical, developmental, and cognitive functioning.

Males with the classic form of the disorder have one extra X chromosome, while those with the variant forms can have additional X and, in some cases, Y chromosomes.

Common physical features may include tall stature, lack of secondary pubertal development, small testes (hypogonadism), delayed pubertal development, and breast development (gynecomastia) in late puberty. These features may be associated with low testosterone level and elevated gonadotropin levels.

Healume was known as the "Man from Nowhere" and is suspected of killing up to 50 men, women, and children. In his case, the Klinefelter syndrome meant that Heaulme was incapable of committing rape in what authorities referred to as the "standard" manner. But on at least two occasions, police say Heaulme brought along a male accomplice who sexually assaulted the victim before Heaulme killed her.

He was arrested on January 7, 1992, and charged with the murder of 44-year-old Aline Peres in Brest, for which he was sentenced to 20 years in prison. But he is also suspected in dozens of other murders across France.

In May 1997, the Assises Court of Var sentenced him to life in prison with no chance of parole for 22 years.

Serial killer Bobby Joe Long was another serial killer who was born with an extra X chromosome.

Photo by: Bobby Joe Long [Wikimedia Commons]

Bobby Joe Long [Wikimedia Commons]

He kidnapped, sexually assaulted, and murdered at least 10 women in the Tampa Bay area during an eight-month period in 1984.

In Long's case, the extra X chromosome caused him to produce an excessive amount of estrogen.

During puberty, his breasts began to develop, and he was teased as a result. He also a dysfunctional relationship with his mother, sleeping in her bed until he reached his teen years.

Long channeled his rage against women into raping over 50 women over a 30-year time period. Eventually, his vicious crimes escalated to murder.

Long released his last victim, Lisa McVey, after raping her for a period of 26 hours — and she was able to give police information that led to his arrest.

He is currently on Death Row in Florida.

XYY Syndrome

Conversely, having an extra Y chromosome is known as "XYY syndrome" or "Jacob's syndrome."

In the past, XYY was sometimes called the super-male disease because men with this syndrome were thought to be overly aggressive and lacking in empathy. But recent studies have shown that the men with XYY syndrome do not suffer from an increased risk of any serious mental illness.

Men with XYY are usually very tall, with an average height of around 6 foot 3. Many experience severe acne during adolescence, and may also suffer from learning disabilities and behavioral problems.

Intelligence is usually in the normal range, although IQ is on average 10 to 15 points lower than siblings.

Photo by: Arthur Shawcross [Wikimedia Commons]

Arthur Shawcross [Wikimedia Commons]

Arthur Shawcross, who was also known as the "Genesee River Killer," famously had XYY syndrome. Shawcross' first known murders were in 1972, when he killed two children in his hometown of Watertown, New York.


Following a plea bargain, he was allowed to plead guilty to manslaughter, and sentenced to 25 years behind bars. But he was paroled after 12 years, and soon trawling the streets in search of prostitutes to kill.

Shawcross murdered the majority of the rest of his victims between 1988 and 1989. He was convicted of 11 murders, and sentenced to life in prison. He died behind bars in 2008.

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