Abigail and Brittany Hensel entered the world on March 7, 1990. The words out of the obstetrician’s mouth said it all: “They’ve got one body and two heads.” Still under sedation, the mother, Patty, heard the word “Siamese” and asked, “I had cats?” But no, she had had what people often called Siamese twins, two babies with their bodies connected even after birth.
Abigail and Brittany are conjoined twins—their bodies are physically connected to an amazing degree. Each has her own head, neck, nervous system, heart, esophagus, and gall bladder. Yet they are parapagus, or joined at the side, and share many organs. Together they have three kidneys, four lungs (two of which are joined), one small intestine, one large intestine, one pelvis, one bladder, one set of reproductive organs, one liver, and one ribcage. Their spines are joined together at the pelvis, and they have just two legs and two arms. (A third undeveloped arm was removed from their chest when they were infants.) They are one of only four sets of two-headed, or dicephalus, parapagus twins in history to survive infancy.
Even more astonishing, Abigail and Brittany can live much of a normal life. The sisters learned to walk by the age of 15 months, a remarkable achievement given that each girl controls just one side of her body. They have had to figure out how to work together in a way much more intense than other children. To do something as ordinary as walking,
Abigail and Brittany have to agree on which direction to go; if not, they go in circles. In fact, they are a model of cooperation: they play piano (Abigail the right hand and Brittany the left). They swim, ride horses, play basketball, type, and respond to e-mails—all without having to speak. Each girl passed her driving test and is licensed to drive. Abigail controls the pedals, radio, and defogger, while Brittany is in charge of the lights and turn signals. They coordinate steering.
Although they share more than other twins do, Abigail and Brittany are quite different in personality, likes and dislikes, and ambitions. Their tastes in food are different, and they experience separately the need to sleep. Sometimes they dress with different leggings, shoes, and necklines. In school, Abigail and Brittany are good at different subjects. They buy tickets for two seats at the movies, and celebrate their birthdays on separate days. As Abigail puts it, “I don’t have two heads!”
What makes Abigail and Brittany so different? How do humans develop, and what does that variation tell us about the essence of being an individual? At what point during human development does someone become a person? As we will see in this chapter, conjoined twins are only one of the many potential variations in human development.