Juan and Carlos are identical twins. Juan was raised by his father and mother, and Carlos was accidentally placed with another family after a "mix up" at the hospital. At the age of 15, both boys "ran into each other" at a football game and noticed how they appeared to be "mirror images of each other." After proving they were twins by genetic testing, the families discussed some of the differences between the boys. Juan is very athletic and intelligent and excels in basketball but does not take school seriously and has F's in all subjects. Carlos is also athletic and intelligent, and excels in baseball and makes straight A's as a result of his strict home life and study routine. Although they are identical twins, what do you think accounts for the differences in their academic performance based on the research?