Men commit more crimes than women do. A lot more. This holds true over time and across cultures. In America, the incarceration capital of the world (more than 2 million detainees), males comprise 93% of the prison population. Men also account for 73% of all arrests and 80% of those charged with violent crimes. This disparity between the sexes is particularly stark when it comes to murder: 90% of the time, the ones who do the killing are men.

All these numbers add up to what criminologists call the “gender gap”. But read enough academic journals and government crime reports, and some curious facts emerge: while crime rates in the western world have steadily declined over the past three decades, the number of young women being convicted for violent crimes in some western countries has increased significantly; law enforcement records indicate the opposite is true for their male counterparts. In other words, the gender gap is closing.

In some UK cities, the number of female arrests increased by 50% from 2015 to 2016. That’s more than a blip. A 2017 report by the Institute For Criminal Policy Research at Birkbeck, University of London came up with this sobering data point: the global female prison population has surged by more than half since the turn of the century, while the male prison population increased by just a fifth over that same period. Women and girls may account for only 7% of all incarcerated people today, but their numbers are now growing at a much faster rate than at any time in recorded history.

Kelly Paxton, a Portland, Oregon-based private investigator known as the Pink-Collar Crime Lady, says she isn’t surprised that female arrest rates are going up: “Women suddenly have the financial pressures that men have had for decades. They’re the breadwinners in 40% of all households. If these women can’t pay the bills, some will resort to committing crimes.”

The new crime trend hasn’t gone unnoticed. The National Herald ran this story last month: Greek cops nab teen girl pickpocket ring in Athens. And here’s a recent BBC News headline: Sharp rise in women caught carrying knives (up 73% in the past five years). Even InSight Crime, a not-for-profit that studies organized crime in Latin America and the Caribbean, is all-in. One of their recent reports sounds like a Netflix elevator pitch: female prisoners in Venezuela become cell block bosses to survive.

What’s really cemented this pulpy women-behind-bars image in the collective conscious, though, is Crime Has No Gender, a controversial Europol campaign that launched last August. “Are women equally capable of committing serious crimes as men?” reads the news release. “The female fugitives featured on Europe’s Most Wanted website prove that they are.”

Are women equally capable of committing serious crimes as men? The female fugitives featured on Europe's Most Wanted website prove that they are

To show that women can be vicious sociopaths too, Europol asked 21 of the 28 EU member countries to select a single fugitive for their campaign. The methodology may have been flawed, and the sample size small, but the gimmick worked. The bad girls theme was reflected in the head count: 18 females, three males. Elena Puzyrevich (Russia), who trafficked nine young women into Spain and forced them to work as prostitutes, made the list. So did Dorota Kazmierska (Poland), a 44-year-old femme fatale who killed her husband by shooting him in the head. Then there’s Zorka Rogic (Croatia), a blonde desperado who works in sales: narcotics, “psychotropic substances”, firearms, munitions and explosives.

Documenting the rise in female crime is one thing. Explaining it is quite another. Cesare Lombroso, the Italian physician known as the “father of modern criminology” (he invented the first lie detector) also wrote the first book about women and crime, La Donna Delinquente, in 1893. He concluded that women who broke the law exhibited crude male traits. The profile was simple: short, lusty, vulgar and prone to wrinkles. They also had darker hair and smaller skulls than “normal” women. A Lombroso dating tip: beware of girls with prominent lower jaws – they’re likely to commit crimes of passion.

Freud also thought criminal women were more like men. Sort of. He blamed female crime on a “masculinity complex”, which could be traced back to (of course) penis envy. Most women resolved this complex and developed into law-abiding citizens. Others, however, fared worse. Instead of embracing femininity, these women over-identified with males and coveted their floppy organs. Think of a woman who smiles while she stabs her husband to death in bed, and later cleans the sheets.

Biology and psychology theories are still discussed in criminology classes today. Studies that link the menstrual cycle to female crime have persisted for decades. According to the three female authors of The Curse: A Cultural History of Menstruation, the 19th century axe murderer Lizzie Borden butchered her family because “her period coincided with an epileptic attack”. Psychology models, of course, continue to be popular. Behavioral theory suggests that becoming a criminal requires conditioning, a form of learning that involves positive reinforcement: rob a bank, spend the money, rob another bank.

According to three female authors axe murderer Lizzie Borden butchered her family because "her period coincided with an epileptic attack"

Increasingly, though, many of today’s gender gap theories focus on external factors, like tougher drug sentencing laws (25% of women in US state prisons have been convicted of a drug offense, compared to 14% of male prisoners) and the proliferation of violent female gangs (the Bad Barbies, an all-girls “sister gang”, with chapters in Harlem and Brooklyn, have pulled off multiple revenge murders). There’s also the post-conviction barriers that uniquely affect women and lead to recidivism: prison guard abuse, few mental health services and a lack of job training. Police, lawyers and judges being less protective toward women is another reason criminologists believe the gender gap is shrinking.

We should have seen this coming. In 1975, the famous criminologist Freda Adler trumpeted this warning in her bombshell book Sisters In Crime: The Rise of the New Female Criminal: “In the same way that women are demanding equal opportunity in the fields of legitimate endeavor, a similar number of determined women are forcing their way into the world of major crimes.”

Forty-five years later, Adler’s feminist manifesto still resonates. Just try finding a criminologist who doesn’t own a dog-eared copy. Critics may argue that her prediction was wrong (the 70s women’s lib movement didn’t breed a vast army of females toting guns and flashing armpit hair), but Adler was onto something. More women are committing violent crimes. It just took longer than she expected.

The most intriguing academic paper that explores the women behaving badly phenomenon is the 2015 article The Darker Side of Equality? The Declining Gender Gap in Crime. Rejecting Adler’s gender equality theory, the authors offer a reverse hypothesis: the real reason that the gender gap is shrinking isn’t because women are copying the behavior of men and committing more crimes – it’s because men are copying the behavior of women and committing fewer crimes. The idea that feminism might be making our mean streets safer may sound absurd to a beat cop, but the theory is being hotly debated among criminologists and gender studies scholars at liberal arts colleges.

The Pink-Collar Crime Lady has her own gender gap theory, and it doesn’t have anything to do with feminism, chivalrous judges or menstrual cycles. “Women nurture and raise us. We love and trust them,” explains Kelly Paxton. “So being a female crook is the perfect cover.” Then she shares some insider wisdom: “The first thing I tell clients is never underestimate a woman. They’re ruthless.”