The list of people who suffered from genetic disorders throughout history is lengthy—and fascinating. Many of the disorders actually give you a good sense of why a person acted or looked a certain way. For example, President Abraham Lincoln (1804–1865) was tall and lanky, a symptom of Marfan syndrome, a genetic disorder that affects 1 in 5,000 people; it most often affects the body’s connective tissues. Another genetically affected person was King Charles II of Spain. The inbreeding of the early European royal families took its toll on many of the offspring, making it possible for genetic defects to pair up. This was the case with King Charles of the House of Hapsburg, who had what is called the “Hapsburg Jaw”—an exaggerated protruding jaw from inbreeding (called prognathism) that caused him to have problems not only with chewing, but with talking.

This is actually two questions. First, can intelligence be measured quantitatively? And second, does a correlation exist between intelligence and certain genotypes? The answer to both questions is a definite no. As our definition of intelligence has evolved, it has become more difficult to assign a single number to the trait of intelligence. Therefore, it is almost impossible to demonstrate what gene sequences would correlate to high IQ values. And while our understanding of the genome is broadening, so too is our definition of intelligence. It becomes less and less likely that we will be able to find one or two genes that determine all of the facets of intelligence, considering the importance of environment in determining “smartness.” Thus, our specific IQ is most likely created by many factors other than genetics.