Intelligence is difficult to study due to the fact that there are an ample amount of variables that influence a person's intelligence. There are also different types of intelligence. The different types include the ability to reason, plan, solve problems, think abstractly, and understand complex ideas. Many studies focus on IQ for a quantitative measurement of intelligence. Based off of the article written by Genetics Home Reference, about 50 percent of the difference in intelligence among individuals are from genetics. Scientist's believe that many genes are involved with intelligence. However, environment has a huge impact on someone's intelligence.