Nature vs. Nurture

I am always fascinated by the nature vs. nurture debate, and love to find examples to support each. ( Can you say Psych major?)Anyway, today we met a friend from our ward and her twins, a boy and a girl, at our new park. Ben and Grace were super excited. Grace kept telling Ben that he has to play with Jared and she has to play with Lydia. I thought that this was just Grace talking, but it actually worked that way. The boys had started wrestling in the grass, and Grace thought they were dancing, so she and Lydia started playing ring around the rosy. Watching the boys wrestle and play the "Mean Game" while the girls danced and sang was so funny, and got us Moms talking about the whole debate. Both boys are only boys, and Jared has a twin sister and two older sisters. Yet they are both such little boys, rough and tumble. How does this happen? How are those traits instilled in someone? It was really funny!