As in other advanced countries, statistics show that most crimes in Japan are committed by males, especially violent offenses.

But explanations for this can be as varied as the crimes, and range from the sociological, environmental and childhood imprinting, to physiological, biological and genetic differences between the sexes. The factors at play that may create a violent criminal could in other circumstances form a personality whose aggression is instead channeled into, say, professional sports.

Studies into causes of criminal activity, including research on physical and environmental factors, were virtually nonexistent in Japan up until a few years ago, when a rise in heinous crimes committed by minors spurred a hard look.

According to a Justice Ministry 2004 white paper on crime over a span of about 30 years, men accounted for roughly 80 percent of all crimes recorded, including violent and white-collar offenses. The figure for 2003 alone stood at 79 percent.

In 2002, police recorded 2,854,061 crimes nationwide, excluding traffic violations. Of the total, 2.8 percent constituted violent crimes. In the same year, the figure for the U.S. was 11,877,218, and in Germany it was 6,507,394, according to the white paper.

"The man-woman ratios for crimes in most developed countries are quite similar to Japan's: 8-to-2, although the figure for women in the U.S. is slightly higher," said Kenji Kiyonaga, a professor of integrated arts and social sciences at Japan Women's University.

According to Yuri Morita, director of Empowerment Center, a nonprofit organization in Nishinomiya, Hyogo Prefecture, it is difficult to pinpoint what types of people commit crimes. Her group trains specialists who handle human rights issues, including domestic violence and child abuse.

But Morita argued that the typical profile here of a violent criminal -- having a poor, uneducated background, being a foreigner or mentally ill -- are pure misconceptions.

"The only profile detail clearly distinguishable in criminals is that most are male," she said. "But this is barely discussed or looked into, as people see it as a matter of course."

Hiroko Goto, a professor at Chiba University Law School, said her research indicates that statistics on crimes committed by women in Japan are low because society expects them to play a less aggressive role than men, women, mainly home-bound ones, have fewer opportunities to commit crimes than men and there is a gender bias in the legal system that means women are less likely to be prosecuted.

"Women have internalized (social) expectations for them to be docile, as opposed to being strong, which is expected of men," said Goto, who also teaches at Keio University and Nihon University.

"Derogation is believed to occur when one has conflict with his or her (social) role," Goto said, adding that one such example is marriage, which "has long been seen as a deterrent to keep women from committing crimes." She said that as long as a husband brings in money, there is no need for the wife to steal.

Because marriage often confines women to the home in Japan, the people they can hurt are often limited to family members, she said, noting women commit most of the child-killings here.

Goto added that women are also less likely to be linked to corruption, as they often lack the career position to become involved in bribery and other white-collar crimes.

In cases where women have a male accomplice, the nation's prosecutors and courts tend to be lenient toward women, assuming they played a subordinate role in crimes, she said.

Even in cases where women have murdered their children, the bias in the legal system has led to sentences being almost always suspended -- at least until the problem of child abuse started to gain wider attention -- as children are often seen as a woman's property, Goto noted.

Besides sociological explanations, endocrinologists say the disproportionately high number of male perpetrators of violent crimes is caused to some extent by chemical influences stemming from the physical environment.

According to research by Akira Fukushima, professor emeritus at Sophia University and a criminal psychologist who examined CT brain scans of juvenile criminals, males who display sudden, violent behavior often have brain abnormalities that may have formed in the womb or shortly after birth.

One of his research subjects was the ringleader of a group aged 15 to 18 who abducted and held a high school girl for 41 days in the home of one of the youths in Tokyo's Adachi Ward in 1998, repeatedly raping her and eventually beating her to death, as the parents living in the house did nothing.

Chemical substances are suspected causes of brain abnormalities, particularly endocrine disrupters -- chemicals that mimic the functions of hormones and may trigger, suppress or impair behavioral development and growth of the immune system.

Fukushima's research shows endocrine disrupters can be passed from a mother to an embryo or to a newborn via breast milk, and the substances tend to damage boys' brains more than those of girls. The reasons for this are being investigated.

Another mystery is why male babies are more vulnerable than females to synthetic chemicals such as progestational hormones, which are given to women who repeatedly miscarry. These chemicals can reportedly super-masculinize boys and make them aggressive.

Yoichiro Kuroda, the principal investigator in a project titled the Effects of Endocrine Disrupters on the Developing Brain, under the government's CREST (Core Research for Evolutional Science and Technology) program, believes polychlorinated biphenyls (PCBs) and glufosinate can hamper the development and activity of the brain.

PCBs are "mock hormones" -- endocrine disrupters that cause neural development defects by disrupting gene functions and neural-network formation in kids -- resulting in lower IQ scores and hyperactive tendencies, he said.

Glufosinate, widely used in the U.S. as a super herbicide for herbicide-resistant genetically modified crops, is like a "mock neurotransmitter" that has an aggressive effect on brains, he said.

If an embryo or a baby is exposed to the chemical, it can affect behavior, as it disturbs gene functions that regulate the developing brain, he said.

A decade ago, the late Toshiko Fujii, a one-time professor of medicine at Teikyo University, conducted research in which she found that the main component of this GMO-compatible herbicide had adverse effects on the brains of baby rats.

"Male rats often fight one another, but female rats are peaceful," Kuroda said in explaining Fujii's research.

"But female rats born from mothers that were given high doses of glufosinate became aggressive and started to bite each other -- in some cases until one died. That report sent a chill through me."

He said there is a considerable possibility that fetuses and babies are also affected by the substance, and since it is widely assumed that males are more aggressive to begin with, it is possible they are more affected than females.

"The chemical industry has not been considering this kind of risk on the developing human brain, which is a fragile, fine chemical machine," he said.

Morita of the NPO Empowerment Center said she fears social attitudes toward violence worldwide are changing in a way that places greater weight on the idea of "might makes right."

"Comprehensive, systematic research on the fundamental reasons behind violence and male behavior" is needed to change both individual and social attitudes toward violence, especially when it takes on a criminal nature, she said.