BJ has had this 'phase' of hitting and hair pulling for a while now. At this point it isn't a phase, because with a child so little (my eldest is only a few months younger) you can very easily teach them what to do instead ('kiss mummy, don't bite her. Look, like this, mwa mwa') and they will copy you. You can also easily distract them with somethint else, as many times it's out of boredom or wanting attention. Trying those things, my little one stopped pulling my hair after a couple of times of explaining it, and I didn't need to read some book on parenting about it. It's just common sense!
If she had the genius Ron claims she has, BJ would have understood it is the wrong behaviour by now and stopped doing it. Ive never wanted to diagnose her with learning difficulties just based on the glimpses of content we see from her but now I am starting to think otherwise.