One of the most common definitions of intelligence is a person's ability to learn and apply knowledge (Howard Gardner's Multiple Intelligences). Humans use our brains and intelligence every day, and the human ability to think and create is what allows us to be the dominant species on Earth. However, there has always been a gap in intelligence levels within our species. There are geniuses and they can solve complex math equations without hesitation. On the other hand, we have a large percentage of people who have learning disabilities, such as mental retardation. Scientists have discovered that there are many factors that influence an individual's intelligence, both positively and negatively. Many connections have been made between intelligence, genetics, and biology, but many scientists have also discovered that the environment in which a person grew up also plays an important role in intelligence. In the 21st century, the causes of high or low intelligence have not yet been completely determined, and scientists and researchers debate many theories and ideas. Your DNA is made up of hundreds and thousands of genetic sequences that make you, you. Your parents contributed to your genetic makeup, so half of your genes come from your mother and half from your father. Many scientists and researchers have determined that approximately 50% of intelligence is hereditary (Causes of Intelligence). The genes you inherited from your parents give you clues about how you are built. Thus, the structure of the brain can differ depending on each person's genes. Your genes determine how your nerves are wrapped in myelin. Myelin is a fatty insulator in the brain used to transmit nerve signals (More evidence than intelligence). The thicker the myelin, the faster your brain works...... middle of paper ......Genes, but where? Association for Psychological Science, October 2, 2012. Web. May 21, 2014. .Mental retardation. Advameg, 2014. Web. May 21, 2014. More evidence that intelligence is largely inherited: Researchers find that genes determine the brain's processing speed. Science Daily, March 18, 2009. Web. May 14, 2014. Scientists “locate” information. BBC News and Web. May 14, 2014. .The 3% solution. The Economist Journal, May 10, 2014. Web. May 21 2014. .