I was just sitting here thinking.
I'm left handed. My right hand is there more to balance my looks and type than anything else. lol The twins, who I carried, are ambidextrous. They will often mirror each other, on purpose. And they switch off who's using which hand. The grandparents are convinced that Katie's right handed and Kim's left. They've obviously done this with all the relatives, to give them a way to tell them apart, because we've even caught the little scamps answering to the wrong name when one anyone but Rachel, my cousin or I call them. He, the cousin, is convinced they're doing it out of mischief. Rachel came up with the thought that they were probably doing it so the relatives could have a way to tell them apart.
Anyway, Rachel's right handed, and Faith, who she carried seems to be leaning more to left handed as she gets older.
Erin's showing every sign of being a born righty.
So, what do you think affects handedness? It can't be entirely genetics.