The Nature and Nurture of Twins by Elizabeth M. Bryan

Occasionally, the firstborn boasts of his/her superiority.  - P. 122
As the first born I find it used against me more than in my favour.  Rachael uses being the younger twin as an excuse to do things second.  For example, when we first got our ears pierced, about aged 7, I had to go first because 'you are the oldest'.

The dominant twin tends to talk more than his/her partner.  It is not uncommon to find pars of 5 year old twins in which one answers all the time regardless of who is asked the question. - P. 124
I was the talker, Rachael was the walker.  Rachael depended on me to voice her opinions until about the age of 6, and generally got bossed around by me and did as she was told.  I depended on her to do things for me, whereas she depended on me to make her view heard.



It is often said that MZ twins can be mirror images of each other which means that they have lateral asymmetry including the superficial features such as birthmarks and hair whorls, the reversal of organs (situs inversus) and opposite handedness.  It has been thought that this lateral asymmetry would arise from the late division of the embryo when the left and right sides have already been determined. - P. 126

We have identical light and dark streaks in our hair and moles and freckles in the same place, but on the same side opposed to opposite.

Cryptophasia

Much has been made of the 'secret language' of twins.  There is no doubt that this cryptophasia or autonomous speech, a language quite incomprehensible to others, does exist. P. 130

My mam remembers us talking to each other as toddlers in twin code, which neither her nor my dad could understand.

Twins together can make a powerful unit.  If they combine forces to be disruptive they can cause chaos in a class and are then better separated as also where one tends to distract the other.  Many twins use their 'twinship' to confuse teachers and entertain other children.  This is harmless fun in small doses but can become a destructive and attention-seeking habit.  Phillip and Watkinson (1981) found that 24% of twins played tricks of identity with teachers. - P. 137

We were never disruptive children, we had no need to fight for attention, because we always had the attention of each other.  We did swap name badges in reception, aged 4, and would sneak into each others classes, but as we got older the teachers could tell us apart so trickery was much harder.

Elizabeth M. Bryan (1983). The Nature and Nurture of Twins. East Sussex: Bailliere Tindall. P 122 – 139.