Sam and Steve were born on September 15, 1972, to Laura and David Brown. Sam was a jolly baby who smiled and cooed at his parents and others. Steve, on the other hand, cried frequently, did not adapt well to school, and did not enjoy playing with others.

For the first five years of the twins’ life, Laura stayed home with the children while David continued working at a local factory. She always seemed to favor Sam and considered Steve her difficult child. David seemed sympathetic to Steve, but the marriage was not a strong one and he increasingly spent less time at home, preferring a local pub. Finances were a struggle for the family and, partly due to David’s drinking, he rarely came home with a full paycheck. Laura eventually took a job as a server in a nearby restaurant to earn extra income for the family, leaving the children with a neighborhood sitter. However, she soon began staying at the restaurant after her shift, drinking heavily. Inebriated, she would come home late at night, often waking the children and demanding that they complete chores such as cleaning their rooms or scrubbing the toilets. She frequently hit both twins but was particularly abusive to Steve, often calling him “worthless” and a “loser.” David continued to spend his days working at the factory and evenings drinking; when Laura abused the boys, he left the house or remained silent. On weekends, he earned extra money as a handyman. The twins attended school and spent after school hours with their grandmother. When the twins were fourteen, Laura left the home. Since her move, she has had contact with neither David nor the twins. The couple subsequently divorced, and David assumed responsibility for the twins with the help of his mother.

At age sixteen, after a serious fight with his father, Sam moved in with his grandmother, dropped out of high school, and worked as a busboy in a local restaurant. Adults in his life encouraged him to re-enroll in school a year later, and he eventually graduated. He reconciled with his father, took out loans to attend college out of state and eventually earned a Bachelor’s degree and a Master’s degree in Education. He is now married, teaches middle school science, and coaches his daughter’s soccer team.

Steve has battled substance abuse since age thirteen. He was frequently truant from school and was arrested for vandalizing the school. Although he was never placed in juvenile detention, he was considered an at-risk juvenile and was enrolled in a number of special programs, including counseling, substance abuse, and anger management. Steve had a close network of friends, all of whom had difficult backgrounds and have been in trouble with the law. At age 17, Steve became a father to a girl named Abby, whom he sees on occasion. She is now 3 years old. Recently he tried to use Abby’s name and social security number to obtain credit cards, because his own cards had high balances that he was unable to pay. Steve has never held a job for more than a month.

Explain the differences between Sam and Steve from a neurobiological perspective. What do we know about their biological make-up? What additional information would be helpful to have?