My daughter bit and pinched her brother today. She is 3.5. She hasn't bitten in over 6 months, but she bites. Luckily, she has never bit anyone besides her brother (and me when she was a baby).
I honestly think a lot of it is instinctive. I know I was a biter as a kid, and to this day, I still clench my jaw when under lots of stress.
I've been working with her on different approach shes can use if she finds herself wanting to be physical. We also have a "no sweets for unsweet" girls policy in this house, and yesterday, after she pinched her brother, I took away videos. She hasn't hurt him in months, but with the time change, she is exhausted, getting two hours less a night. I am hoping that once she recovers from her current cold and her sleep deprivation, she will start being able to control herself a bit better.
I look forward to hear what others say on this matter.
Oh, I have found social isolation to work wonders to. When she is mean to her brother, she is not allowed to play with him anymore. She hates that.