[bugglebeetle]

The twins I have known are the same. I would assume it has something to do with a desire to differentiate themselves from one another, but they always seemed far more dissimilar in personality and affect than my siblings.

[riffraff]

OTOH could be siblings tend to be more similar as the smaller ones try to copy the older ones (my son would dress up as a ballerina to play with his sister when he was little, my smaller brother would acquiesce to play chess with me just to spend time together etc).

I have given up trying to explain child development, there's just too many variables.