Interesting discussion on why sibling personalities can be so different. According to this piece, we are similar to our siblings less than 20 percent of the time.
The fact that children compete for the love, time and attention of their parents results in kids being pushed in opposite directions. When one sibling is good at something, the other will focus on something else to minimize competition, even if the second sibling may be talented by societal standards.
Since my brother was adopted, our significant divergences can be explained by different genetics. My husband has two genetic siblings. I see certain characteristics he shares with both of them, but personality-wise, they are all pretty distinct. Mark was the most difficult one to parent – the most colicky, sensitive, stubborn and independent.
River’s easy, mellow, thoughtful and sensitive personality has been so ideal for us. We are really rooting for a sibling with his personality. But we have less than a one in five chance of getting it. So we must be prepared to adapt, to treasure the differences, and to adjust to a personality that in all likelihood, will be more challenging to parent.