The lives of twins bring many mysteries to psychology as well as sharing a unique perspective on the effects of genetics vs environment on a human being, but how would it effect you to share not only an environment but a body with another person? I growing up i knew two Dicephalic Paragus twins, more commonly referred to as "conjoined twins", who deal with the implications of this condition daily.
When a single egg attempts to separate into two embryos and is somehow restricted in the process of splitting or two fully separated embryos are somehow forced back together, the two eggs will form a partially intact body depending on when the restriction occurred. Conjoined twins can take on many different levels of attachment and independence.
In Brittany and Abigail's case, each girl has their own heart, lungs, kidney (actually contain 3 in total), stomach, spine, spinal cord, gallbladder, and most importantly brain. As one moves down past the stomach, the girls anatomy merges together to form one oversized and surgically modified ribcage, one diaphragm, one breast each, an enlarged pelvis, one liver, one intestine, bladder, and one set of reproductive organs.
Many of you may have seen the twins in an old TLC documentary. A clip from the documentary is attached below.
TLC documentary clip
Here is a more recent news report on the girls seen on ABC earlier this spring, as well. ABC News story
Abigail and Brittany's situation brings up many questions. With one set of sex organs, how will the girls cope with the social implications of marriage and children?
Brittany's recent engagement has brought changes for the girls in learning to cope with the legal implications of marriage in their unique situation
Conjoined twins also bring up the question of growth and development. In what ways did Abigail and Brittany develop differently to function in unison?
With each controlling one arm and one leg, the two must constantly work together to preform simple tasks like clapping, and getting ready in the morning. Other more complicated tasks like driving and biking have forced the girls to rely more heavily on each other. For example, only one of the girls controls the foot pedals in the car. One body also means compromising on how time is spent. The girls say that they often take turns choosing what to do.
How do their physical contraints limit the individuality of their intellect and decision making?
Some teachers have let the girls take tests together (because one will always have the information the other needs right?), while others see them as two individuals and thus force them to take tests separately. The pair took two driving tests for each to receive their own licence. the girls seem to have separate personalities and interests implying that genetics serve a large part in personality seeing as they have lived close to identical lives.