This is an excerpt from reporter Scott Johnson's blog, which focuses on the effects of violence and trauma on the community. Go to www.oaklandeffect.com for updates on his reporting.

No sooner had Darisha Fields and Adrianna Smith left the Rene C. Davidson Courthouse in downtown Oakland one day last year when about 20 girls swarmed around them and began shouting. The two women tried to push through, but the group of girls closed in. They were shoving and threatening. Suddenly, Fields, who was eight months pregnant, felt a fist come cracking down across her cheek. In the melee, Smith was struck as well, also in the face. By the time the two women managed to escape and the police emerged from the courthouse, the gang had disappeared.

Fields and Smith had been in court to attend a preliminary hearing for the man accused of killing Adam Williams, a 22-year-old after-school teacher who had fathered a child by Fields and had dated Smith. The two women had been good friends for years. Williams had been gunned down in the early morning hours in April 2011 while having a drink at Sweet Jimmie's bar near Jack London Square.

His family had suffered while following the court proceedings in the months since the murder. One day in particular stood out, when about 50 young people, many loud and belligerent and making threats, had filled the courtroom to give support to the accused. But mostly, says Prince Williams, Adam's stepfather, they were there to intimidate the family.

I've written about intimidation here before. It can change the dynamic of a neighborhood in dramatic ways, forcing innocent residents to stay indoors for fear of being attacked. I wonder what other effects it can have, however. If you live in a tough neighborhood, for example, does it help to be aggressive to survive? Is aggression, as Darwin might say, an "adaptive" trait in those circumstances?

Last year, I spoke to two freshman girls at a small high school in Oakland who found themselves on the receiving end of a rapidly escalating intimidation campaign being waged by a much older female member of the Norteño street gang. One of the two girls, Susie, had a brother who was an active member of a rival gang, the Border Brothers. Her best friend, Rebecca, had no such connection herself, but her close friendship with Susie was enough to raise the wrath of the older girl. As soon as the Norteños discovered that Susie's brother was a sworn enemy, the girls got swept up into a war by proxy, a war they never wanted and from which they are having a hard time escaping.

The harassment started out as a sort of whisper campaign. Both Rebecca and Susie started hearing rumors that the older girl was looking for them. They started watching their backs in their Fruitvale neighborhood. Then both girls began receiving threatening messages via Facebook and Twitter. And then one day when Rebecca was about to leave school a friend rushed up to her. "She's here," the friend said. "She's waiting outside." Rebecca was smart enough not to venture outside right away, and by the time she did, the older girl had disappeared. But the threats kept coming, and over the next several months the lives of both girls were turned upside down.

Within weeks Rebecca and Susie transferred to another school after their teachers told them they couldn't guarantee their safety on campus any longer. They became so fearful of what might happen that they stopped leaving their houses. Rebecca stopped going on Facebook, scared of what she was going to find written on her wall. Susie began popping tranquilizer pills to take the edge off.

The parents of both girls considered sending them to stay with relatives in Mexico. Susie's father even went so far as to reach out to the father of the Norteño girl to plead for an intervention, only to be told that the girl was out of his hands and that he could no longer control her.

Within six months, what had once been a strong friendship began to crack and fissure. Susie's grades dropped. Rebecca, once vibrant and socially outgoing, retreated into a shell in her new school. The intimidation threw both girls into depression, anxiety and fear.

Living with constant threats comes with a price. Surviving in tough circumstances like these leads to a shift in the body's biochemistry. Senses are on high alert all the time. It pays to be scared because being scared might save your life, but that also means being in a state of near-constant excitability, which means less concentration for school work, decreased ability to regulate stress, heightened sensitivity to danger. No wonder the friendship between Rebecca and Susie cracked.

On the flip side, some people are adapting to these circumstances and even thriving in them. The question is how to address the needs of both groups of people with limited resources. I think this is something policymakers should be thinking about.

Contact Scott Johnson at 510-208-6429 or scjohnson@bayareanewsgroup.com.