I interned at and worked for a NP company in New England for a few years that was kind of a heartbreak conglomerate. They ran homeless shelters, soup kitchens, women's shelters, alcohol rehabs,prison outreach programs and detox centers in prisons and the big cites of New England. In order to get funding from the states and the feds, they are required to collect mountains of statistics and perform continual studies of the populations they serve. From such places liberal computer programmers are born.
The women's shelters were pretty sad. Children were involved, and there was always a possibilty of violence, and the women were either in total terror or had been driven stark raving nuts by their spouse. I can give you a quick gist of the general results of studies in this area. Violent men come from three catagories:
1) Those who were badly abused themselves when they were children.
2) Those who have been addicted to a chemical, the two worst of being alcohol and methamphetamine
3) Those who are socio-pathic, a term that means that someone for some unknown reason has been born with out a conscience, the same class of people who make up rapists, serial killers, con men and child molesters.
1 & 2 will respond to treatment appropriate to the problem. They are the vast majority of people who are involved in what is called "domestic violence", many times by people who are not really prone to this behavior but under the influence of drugs or in a stressful situation they resort to violence, however when the situation is over or they sober up, they are genuinely remorseful for what has happened. These people need help and should be treated with compassion if they genuinely want help. If they don't, the smart person needs to understand that they are asking for a life of hell if they continue to live with a person in one of these catagories. 1 is usually treated with anti-depressants, 2 with rehab and a lifetime in AA, NA or the like. If so, they have an execellant chance at a happy, normal life, that is if they can manage to stay out of prison.
#3 is a great area of controversy, but after years of studies, the vast preponderance of evidence is that these people can never be cured, and I myself strongly believe it. Even being the liberal that I am, I can see where a strong case can be made for putting these people to death, as they simply carry on their work in prison, and even prison inmates have a right to be protected from these men who are essentially predators, in fact the current thinking on why US prisons are so bad is because we let these guys loose in the general population, hence the new trend towards "supermax" prisons. If we aren't going to kill them, we need to at least put them in a plexiglass box by themselves.
The general theory on it goes something like this: our brain is like an onion that evolution is constantly adding layers to. On the most recent outer most layers are our capacities of higher feelings, love compassion etc, and as a group they make a functional part of ourselves we call the conscience. Some people are born without it. As a result, they are what nature intended people to be at the time in our evolutionary histroy -scheming clever predators who kill, rape and rob to survive. Their cleverness also allows them to mimic the aspects of love and compassion they need to carry out whatever predatorial scheme consumes them. If you are involved with a person who is even suspected of a crime of this nature, or uses beatings or any other type of abuse as a means to control another human being, or acts in ways that show a lack of higher facilities by tortuing animals, purposefully running down pets, any behavior like that, you yourself are in great danger. A lack of a social circle coupled with prolonged periods of unexplained absence during the course of a day is another real clue - these men seem to either subject their immediate families to this behavior, or the public at large, sometimes not simultaneously.
The premier school in the country in this area of study is the University of New Hampshire's Family Reasearch Labatory. They have huge resources you can access and if you are trying to acquire a degree in this area, studying here is like studying at MIT for an engineering degree, they are tops in the field:
http://www.unh.edu/frl/
1/3 is too high an estimate. 8-10% is more like it.
Also beware women who have been victimized who attempt to work in this field. They are usually going to have a bias that effects clinical judgement, and some have a pretty big ax to grind. I am not trying to put them down, thats just a reality that has to be accepted and dealt with. You should find a neutral source to check against when evaluating theory in this area. I'll look into the pituitary gland thing for you, I still do a lot of work in that field. I've never heard of it, but it could be something new.