Siblings Share Genes, But Rarely Personalities

Identical twins separated at birth tend to have more similar personalities than identical twins who grew up together. The hypothesis is that, due to the presence of each other when growing up, they actively (though subconsciously) differentiate themselves. It's reasonable to assume the same effect would happen to some extent with other siblings. The fact that twins (or siblings) are more similar when raised in different environments would seem to contradict the idea that subtly different environments are responsible for the majority of sibling discrepancy.

I'm working on finding the citation. The phenomenon is known as "twinning" but that apparently refers to a bunch of other junk that makes it hard to find what I'm referring to. I may have to dig out my bioethics book when I get home.

As one of three boys born within four years of each other, I support Theory Three: Exaggeration. Yeah, we had differences, which were wildly exaggerated and reinforced, and which pushed us into different universities and it all goes to sh!te from there.

As the father of two now teen boys born within 12 months, they're freaking aliens compared to each other -- except other people can't tell them apart.

It's not my fault.

My two kids had a completely different personality when they were each 2 months old. Their personalities have hardly changed in 4 years. So, none of these 3 theories account for this - I think genetics is a much bigger deal.

My sister and I are completely opposites. I am an introvert, she is a crazy extrovert. She is a crazy risk taker, while I am risk adverse.

Anyone interested in this stuff should read Steven Pinker's "The Blank Slate"...